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What area’s of your grow do you need to optimize.
Select and start growing like a PRO
If you look at the edges of a seed, you’ll notice that there’s a seam all the way around, and that it’s more pronounced on one side – like a ridge. This ridge comes off quite easily and then allows the seeds to pop right out of their shells with ease.
Grip the seed between your thumb and forefinger with the ridge side up, then using the sharp edge of a small pocket-knife or paring knife, very gently scrape at a 90 degree angle across the ridge and you’ll see it come right off, exposing a slight opening along the edge of the seed.
Take extra care not to squeeze the seed at all, but spin it around to finish scraping the other end of the ridge (on the same side)
Then put the seed into a small container of room temperature filtered/distilled water without any additives for about 18-24 hours.
Next gently transfer your pre-soaked seeds to a pair of wet paper towels (pre-warmed to room temp), maybe in a large tupperware-like covered container.
Misting the paper towels daily so it stays nice and damp (but without any standing water puddles in the folds of the towels).
Don’t let the towels get too cold, because the wet paper towels will always get chilly fast, so they must be kept in a constantly warm area (but dark). A heating pad may be required to maintain 78f to 80f throughout germination.
I use a regular heating pad set on low, covered with a light towel to buffer the heat, and on a timer, set to go on and off every half-hour. Make sure they are kept in a very temp stable area. I use a digital temp gauge, the kind that cost about $10 US and have a probe on the end of a wire, so you can place the probe right into the wet paper towels.
[editor’s notelace seeds on top of the fridge if you don’t have a rootmat]
Seeds should sprout within a few days; when they do, they must be transferred to the medium with great care when the taproot has come out about 1/4″ to 1/2″. I find that a 1/2″ tap root seems to be the best. When it’s much shorter, they tend to get shocked and die easier, and if it’s much longer, there’s more risk of damage.
They are very delicate at this stage; sprouted seeds can be killed by rough handling, damaging the tap root, or if the soil or medium they’re put into has not been properly prepared in advance to the right moisture and temp.
If you’re using a soil mix, I usually add about 25% perlite and 25% vermiculite to 50% pre-sterilized Supersoil. Using a pencil or something to prepare a hole for your seedling, and lower it in with the taproot down first and the seed end up. Gently pack or fill in the hole fairly loosely around the taproot, covering the top of the seed by about 1/4″, and I water them with an eyedropper or a spray bottle set on mist.
Now you’ll want to place them under fluorescent lighting about 4″ to 6″ away and mist them down daily. Continue to ensure they are kept warm enough, because when the wet medium cools off at night down toward 60f it can shock and slow them down or possibly even kill them.
Authors: Locutus and LoneStar
Mixes composed of perlite, vermiculite, and rockwool and other inert media should be treated with a mild application, 300-400ppm, of fertilizer prior to seed introduction to provide available nutrients and buffer the pH.
Adding Hormex, Superthrive or some other auxin/vitamin based supplement will accelerate early plant development. It is not beneficial to apply additional fertilizer to seedlings in rockwool or other inert media until the first set of true leaves appear, at which point a 1/4 to 1/2 strength application is made.
Excessively rich organic soil mixes are best avoided until the tender, young plants are well established. As such it is possible to feed young seedlings in soil with a 1/4 to 1/2 strength solution of fetiliser after two to three weeks or after the first set of true leaves appear but only if the soil is not super hot in terms of nutrients.
Coco produces excellent results for the soilless grower; it is comparable in result to hydroponics systems.
It is a great alternative to the soil grower willing to experiment with a “soilless” medium, yet get comparable results to a hydro grow.
Coco can be used in a hydroponics system, or just put into pots and watered by hand as with any other soil grow. Countless grows for decades have been produced in plain soil, mixed with organics, compost, and perlite among untold other ingredients thrown in.
While soil does have its advantages, it also has more drawbacks: inconsistancy, unwanted (unknown) ingredients, increased chances of over-fertilizing and over-watering. Nearly all of the potting soil used has been sourced from nature contain larva and insect eggs.
*Pics shown which I grew in Coco are only 30 days into flowering, 60 days old from seed, with an intentional N def. They are not as yellow as shown. I have provided them to show the crystal/pistil covering bud/leaves more common to hydro in this stage of flowering, yet grown in coco-filled pots
The Definition of Coco
Many at first are misled by the use of the term Coco. It has nothing to do with the Cocoa plant at all. In reality, they are the brown fibers that make up the husk of a coconut, which have been washed and buffered. Pure Coco can be used as a substrate, or Coco can also be mixed in with soil.
It can be bought loose in bags; it is also pressed into planks (and bricks). Coconuts are found near beaches, oceans, places that have very salty air. To rid the coco of these salts, the coco is first washed, and then pressure steamed to get rid of salts, and bacteria, germs or anything else that might have been in it. Coco is buffered using water, enriched with Magnesium and lime. The quality of this treatment is dependant to the quality of the Coco. Coconuts cannot be bought from a store, pealed, and mixed into your soil.
(Edit: low quality coco may need to be washed to remove natural salts.)
Coco and PH
The buffering process also means easy adjustment of pH in the Coco, which is imperative when it comes to the optimum uptake of nutrients throughout the plant’s life.
Soil PH can be hard to change, since it takes time to correct, flow check and restore. It takes longer to correct the problem in soil, than it took to cause it.
The PH of fresh Coco is marked on the bag from 5.0 – 7.0, however all of the coco I’ve tested was always between 6.0 – 6.5. Changing the PH of Coco takes a few waterings of pH-adjusted water, perhaps only one. The medium is very reactive to the PH of the water given to it; this gives coco growers rapid control over pH.
What is important is that you use 6.0 – 7.0 pH water, 6.5 being optimal if in pots.
Oxygen and Coco
Soil has a tendency to become finer after time. The clumps of soil quickly disintegrate, leaving very fine pieces of matter which hold moisture, creating saturated spots, making the soil less and less aerated for roots over the plant’s life. The soil at the bottom of the pots can become a very hostile environment for the roots to grow, making roots suffocate in mud. Coco users rarely find this a problem. Coco almost never disintegrates, leaving the medium well aerated, supplying the roots constantly with enough oxygen, and all saturated spots quickly even out.
Another advantage of Coco is the fact it can be re-used. Because Coco is treated so well, you can get up to three grows from the same batch of coco. Coco is inert and does not absorb nutrients within its own fibers, so plants uptake only supplied nutrient-rich water; excess nutrients and salts are washed through with the overflow.
Before reusing coco, you must sift through the Coco looking for any loose root fragments, missed decaying leaves, ect. and remove them.
Advantages and drawbacks
Coco overall has many distinct advantages over soil. I have yet to grow a plant in Coco that hasn’t reached 2-2.5 feet in just 1 month from seed, without any stretching until later in life (without Topping or Fimming). The evenness of watering and the quick and direct changes of pH compares to hydro. ,
The only drawback to Coco I have found is that a massive root ball forms very quick while in veg., all my plants were detrimentally root bound in 7 Liter (1.85) gallons of coco after only 3 weeks of growth from seed. If you are ready for the growth, being in pots, and hesitant at all to go hydro with supplies and adjustments, it’s just a small hurdle for all the benefits.
18/6 or 24/0, that is the eternal question.
Those numbers refer to the amount of light and dark that the plant receives (18 hours of light / 6 hours of darkness). Anything above 14 hours of light per day will keep the plant in vegetative mode– growing leaves and not buds. When you want to switch to flowering you reduce the cycle to 12/12.
Cannabis plants grow without hassle under 24 hours of continuous light. There has been no controlled recordings of increased hermaphroditism or problems– most growers now use the full 24/0 cycle.
However, 18/6 does have it’s advantages:
* Reduced electricity costs. When you have a good mother plant collection and clone cycle, you don’t need the increased growth the extra light provides. Lowering the cycle will save money.
* Allows the equipment and room to cool down. Those 6 hours of darkness can be timed to happen during the hottest part of the day, providing some relief for growers in hot climates.
The amount of time your garden should be exposed to lighting depends on what ‘cycle’ your garden is in:
The ‘Vegetative Cycle’ of your garden starts with the sprout of the seedlings and can be continued indefinitely. In the veg cycle your garden will require a minimum of 16-18 hours of light and 6-8 hours of darkness daily. Since a given amount of light can only do so much, equal production can be realized in a smaller space with less plants, where the light is concentrated and the plants can grow more efficiently. Using more light helps additional co2 uptake.
Since a plant can be kept in the ‘Veg cycle’ indefinately, many growers cultivate ‘Mother’ plants. This plant is used for clone starts and never produces buds, only new growth.
The ‘Flower Cycle’ or ‘Bud cycle’ is typically equal amounts of light and dark, 12 hours on, 12 hours off or 12/12. This produces a change in the plants metabolism simulating Fall, shorter days….less light.
This is the cycle that the plants will show their sex. Usually, you’ll be able to determine the sex within the first 2 weeks of 12/12. By the 3rd week most plants have developed healthy bud sites or pollen sacks.
The plants will continue on the 12/12 cycle until harvest.
When someone ‘Re-vegges’ a plant that has been in the flower cycle, they’re switching the light cycle back to 18/6 to stimulate new vegetative growth.
Measuring and Changing Temperature and Humidity
In order to properly measure temperature and humidity, you’ll need a thermometer and hygrometer. Best to invest in a digital one that can give you current readouts as well as highs and lows when you’re not inside the room. To raise heat, you’ll need a heater and to lower heat, you’ll need an air conditioner. These can be outside or inside the growing space depending on the size of your space and how much the temps and moisture levels fluctuate. A humidifier and a dehumidifier can be employed to raise and lower humidity rates. Larger grow rooms can benefit from a controller that uses a sensor to keep track of temps and humidity and turns on the appropriate appliance to regulate and keep them within your set parameters.
Because cannabis cuttings root best in warm conditions with high humidity, the cheap trays with clear plastic domes work remarkably well. In cool conditions, a heat mat should be placed underneath the trays to maintain an optimum temperature of 23-25 degrees C. and relative humidity at 75-85%. No matter where and into what medium you plan to root your clones, keep warmth and high humidity on your priority list. Clones allowed to get cold or dry will perish quite quickly. Too much humidity (over 90%) can also cause mold and rot, so cut a quarter-sized hole or two in your clear plastic dome to allow some air movement and circulation.
The Vegetative Stage: Best Grow Room Temperature
The best grow room temperature during the vegetative stage of growth is 21-25 degrees C. when the lights are on during the “daytime” and no more than 10 degrees cooler at “night” with a relative humidity of 45-55%. With these settings, your plants will best be able to convert light into energy for growth. This is the time when the plant puts on leaves and branches and expands it’s root system throughout your growing medium. If it gets too cold or hot, growth stops and you eventually risk losing your plants altogether.
The Flowering Stage: Best Grow Room Temperature
The best grow room temperature during the flowering stage of growth is 20-23 degrees during the day and no more than 10 degrees cooler at night. If you’re supplementing with CO2, daytime temps can be as high as 23-28 or so. During flowering, you should lower your relative humidity to 35-45% and even lower (30%) for the last couple of weeks before harvest. This will help you avoid issues with mold, bud rot and PM (Powdery Mildew) that can arise in higher humidity.
Drying and Curing
The drying room is a place that must be carefully monitored. Keep in mind that your plants will be giving off a large amount of moisture into the room as they dry. It’s important to pull wet air out and keep air circulating in the room without actually having fans blowing right on your hanging branches, which can dry them out prematurely resulting in a harsh taste and burn. Also, growers in dry places struggle to extend their drying time with humidifiers, while farmers in more humid climates such as Coastal areas use dehumidifiers to pull water from the air in order to avoid mold growing on their buds.
The ideal temperature for a drying room is between 18 – 23 degrees C and humidity between 45 – 55 percent in a dark well-ventilated room. Cannabinoids, terpenes, and flavonoids can evaporate and be released at temperatures above 26 degrees, diminishing the scent, flavor and potency of your buds. Within 6 – 10 days your branches should snap instead of bending and the buds should feel popcorn dry on the outside. This is the time to cut the individual buds from the branches and put them into glass jars to begin the curing process. Cure your buds in a cool (20-22 degree C.) and dark place.
What is pH?
pH is one of the most common analyses in soil and water testing. An indication of the sample’s acidity, pH is actually a measurement of the activity of hydrogen ions in the sample.
pH measurements run on a scale from 0-14, with 7.0 considered neutral. Those solutions with a pH below 7.0 are considered acids, and those above 7.0 are designated bases. The pH scale is logarithmic, so a one unit change in pH actually reflects a ten-fold change in the acidity. For instance, orange juice (pH 4) is ten times more acidic than cottage cheese, which has a pH of 5.
Many industries rely heavily on pH for their processes to work properly, or to maintain expensive equipment. Breweries maintain the pH between 4.2 and 4.6 to keep infectious bacteria from breeding during the fermentation process. In many industrial applications, if the pH is too low the water may corrode metal equipment, but if it is too high scaling may result.
pH can be measured visually or electronically. Visual comparisons use a pH indicator whose color change reflects the pH, which is then matched to a color
standard. pH meters, such as the pH 5, simplify the pH test. A probe is placed in
the sample, and the pH is read directly from the meter.
While the meter is very easy to use, the electronics within the meter are more
complex. After the pH probe measures the millivolts of potential between the
reference electrode and the pH electrode, the meter converts this reading to pH
units using the Nernst Equation:
pH is extremely important and one of the most often overlooked parameters by new growers. I know because I also overlooked and underestimated the importance of pH when I started growing.
In CoCo the pH must be between 5.8 and 6.0. Period well + or – .1 some will argue. This is a very finite range. You will find out it does not take much to skew pH too much in either direction. many soil growers battle to keep pH up at acceptable levels while many hydro growers fight to keep the pH down to acceptable levels.
Why pH tends to go low in soil…
Most soil / soilless mediums are comprised of some failry large percentage of sphagnum moss. As this moss degrades and breaks down it becomes very acidic thus effecting nutrient uptake by way of lockout. Certain nutrients/elements get locked out at either too low or too high of a pH. This is noticable by plant show extreme deficiencies of one or more nutrients when you are feeding the plant all nutrients and the leaves may also look crumpled or twisted.
Best way to counter this in soil is to “sweeten” the soil by adding pulverized dolomitic lime which is very alkaline. A little bit goes a long way. It will help keep the pH stable offsetting the acidic breakdown of the moss.
Why pH tends to go HIGH in hydro…
Water with nothing in it is pH neutral. or pH of 7.0
Adding your hydroponic nutrients to the water will tend to bring the pH down. The nutrients them selves have acidic properties. Either naturally or are made this way by the nutrient manufacturer to help get your reservoir to an acceptable pH range. In hydro it tend to be a negative pH shift of about .7 of soil acceptable range. so 5.5 -6.2 or so. In hydro it is beneficial to flux within the range to best absorb all nutrients. So set res at 5.5 let flux to 6.2 then bring back to 5.5 etc.
As the plant absorb the nutrients (remember which are acidic and lowering the pH) from the water the pH will shift north towards neutral.
The more plants you have and the less reservoir space you have will lead to huge fluctuations in a short period of time. Unless you want to stand over your reservoir constantly monitoring and adjusting for pH and PPM then you should plan on 17 ltr or more of reservoir volume per plant.
Because your pH electrode is susceptible to dirt and contamination, clean it
every one to three months depending on extent and condition of use.
Clean the electrode in a mild detergent solution. Wipe the probe with a soft
tissue paper. Avoid touching the glass membrane with your fingers. Rinse
thoroughly in tap water and then in distilled water. Recalibrate your meter after
cleaning the electrode.
The pH electrode should always be stored in the soaker bottle. The cap should
be tightened to prevent leaks. The soaker bottle contains a dilute solution of
Special Cleaning Tips
Salt deposit: dissolve the deposit by immersing the electrode in tap water for ten
to fifteen minutes. Then thoroughly rinse with distilled water.
Oil/grease film: wash electrode pH bulb gently in detergent solution. Rinse
electrode tip with distilled water.
Clogged reference junction: heat a diluted KC1 solution to 60-80°C. Place the
sensing part of the electrode into the heated solution for about 10 minutes.
Allow the electrode to cool in some unheated KC1 solution.
Protein deposits: prepare a 1% pepsin solution in 0.1M of HC1. Place the
electrode in the solution for five to ten minutes. Rinse the electrode with
Hydrogen peroxide is beneficial as an addition to nutrient feeding programs at all times. It feeds the good aerobic bacteria and kills the bad anaerobic bacteria. It also introduces radical oxygen atoms which oxidize elements, making them more available for the roots to assimilate. Apply 3% H2O2 at a rate of 30ml/3.7 ltr to the reservoir. The plants show no visible signs of stress afterwards, which indicates that it was not an excessive application.
Sprouting Seeds: add 30ml 3% H2O2 to 500 ml of water. Soak the seeds overnight.
Insecticide Spray: combine 250ml 3% H2O2 to 3.7 ltr spray mix.
Fast growing container plants: add 30ml of 3% H2O2 to 3.7 ltr water.
Hydroponics: apply 3% H2O2 at a rate of 30ml/3.7 ltr to the nutrient reservoir.
The WHAT, WHEN, WHY and HOW to Flush Your Plants
I know when I started growing, I had never heard of “Flushing”, then I heard a lot about flushing and it was confusing. Even some warnings not to flush.
So, for new growers out there, here’s the What, When, Why and How to Flush your Cannabis plants.
First the WHAT and WHY:
Many folks think flushing is about cleaning out the plants. In an indirect way this is true, but its really much more about your soil and roots and res. When you flush the plants, you are running large amounts of water through the system. Sometimes you will add something to that water to assist – more on this below.
So what exactly happens that you might want to flush? Lets look at the way the plant takes up nutes. Lets use an imaginary nute that has 3 minerals the plant wants : A,B,C. When you buy this nute they know the plant is not going to want the same amount of everything so they balance it for you and put in 10 units of A, 5 units of B, and 1 unit of C.
When you use the nute – the plant loves you for it. You see immediate results. You say to yourself this stuff is giving the plant exactly what it wants. This is unlikely. What is probably happening is that the plant is using what it needs from the nutes, but there is likely some that is not being used as much as others.
So after 3 days your plant may have only used 8/10 units of A while having used up all the B and C minerals. So you look at them, and your ppm meter says feed them – so you add more nutes. Now you have the same original mix of B and C, but there is still A left from before and you’ve just added more.
So, again, the plant takes what it needs. 8 units of the A and all the B and C. Now you have again used all the B and C, but there are 4 units of A remaining in the soil or res.
This would not be a bad thing if the plant could continue to operate this way. Just make sure she has more than she wants, let her take what she needs and its easy right? Unfortunately – its a little more complicated than that.
What happens is that certain minerals interact with other minerals. And when they are in balance you get good consistent growth. But if they are out of balance you will see a deficiency. What is important to understand here is that the deficiency may not be caused by a LACK of one mineral – but an OVER-ABUNDANCE of another. Its odd to think that putting in too much of one will limit another, but this is what’s known as “Nutrient Lockout”. It is much more prevalent in Salt-Based nutrients but can affect anyone.
Just changing the res every 7-10 days is a great way to sort of reset these imbalances. You’ve likely seen PitViper’s magnificent work – he is religious about changing his res every week.
So experienced indoor gardeners (check out LabRat420 – he hasn’t even changed the res in 80+ days as of this writing, let alone a flush, and his colas are thicker than beer cans) can get away with much less flushing because they know how to balance the nutes individually. Outdoor in-the-ground plants are even luckier. Mother Nature is taking care of the flush for them with a crazy thing she does called rain.
For the rest of us, there are some times when its good to flush. Both McBudz and SettingSun include a flush in their schedule and they are Grow Support. Both of their journals are clinics in proper technique.
Like all things in growing – too much of a good thing is bad. And too much flushing is not only a waste of time and money, but you can flush away stuff that can be good for the plants.
There are three basic times/reasons to flush:
1. Pre-Harvest Flush – many folks agree that this will improve the flavor of the cured bud. If you’re using Clearex then you can flush as close as 3 days before harvest. Other methods should be done a week to 10 days before harvest and repeated three days later.
2. When you dramatically change the nutrient schedule – usually when you start Flowering, some flush entering Veg as well. This is a preventative flush. Again – not mandatory, but not a bad idea. Also, in soil, this is about the time the plants have sucked all the nutes from the soil, And before you go jacking it up with your own mix – its not a bad idea to sort of zero it out.
3. If you are experiencing Nutrient Lockout. Usually (NOT ALWAYS!) when you have a dramatic nutrient imbalance the cure is not to try to figure out the exact one, but flush the plants, and add a fresh WELL BALANCED and MEDIUM STRENGTH dose of nutes. Now don’t go flushing at every burned leaf or tinge of yellow. Use common sense. But if you see dramatic problems, and there are no obvious signs of another problem like heat, cold, grey goop in the res, root rot, etc – then its prolly not a bad idea to flush the plants and re-fill the res.
Now that you understand the WHAT, WHY and WHEN of flushing – let’s talk turkey and get to the HOW.
I have experience with the 3 basic techniques: Plain Water, Water with extremely low nutes, and Clearex – there is a time and place for all of them and the method is basically the same. And remember if you have plants in multiple containers – feel free to experiment with multiple methods on the same grow.
I use Clearex and will describe that method in detail. Clearex is a brand name flush from Botanicare. Many folks use plain water or a very, very mild nutrient/water mix just as effectively. I won’t try to make a suggestion on ppm for what a very light mix is, but let me tell a quick story to illustrate.
I had 5 plants in 5G soil that were ready for harvest. I thought. 4 plants did indeed finish in the next 4 or 5 days after the Clearex flush and it was perfect. They tasted great after an 8 day dry and 2 week cure.
The fifth plant, however, was not quite finished. So I decided to give it one more feeding, then wait three days, then flush again using the low ppm method as a test. All the plants had been receiving about 1250ppm the week before. So I fed this one 750ppm with very little runoff. Then three days later I gave it 100ppm with about 50% runoff. Then 4 days later I gave it plain water with about 50% runoff. Then 3 days later I cut it. So the timeline at the end was: Wed – Clearex 5 plants; Sun – Chop 4, feed 1 750; Thurs – feed 100; Sunday – plain water; Wed – Chop. This was wrong. I had not allowed enough time at the end, nor used enough plain water.
I dried that plant exactly the same 8-10 days as the others – ’til her stems snapped fine, then the cure. After a two week cure the smoke was still extremely harsh on the exhale, and the buds crackled when burned. BTW – this is the sure sign of a bad cure or flush – if the smoke tastes fine on the way in but becomes ridiculously harsh on the way out. So I put that bud back in to cure and left it for the last to be smoked. six weeks of curing later – for a total of TWO MONTHS OF CURING – it was still snap, crackle pop and tasted harsh. So I can’t give you an estimate on what low ppm means, but I can tell you what I did was NOT enough of a flush. Perhaps someone who uses the low ppm method effectively can add to this. Now back to our regularly scheduled program with a method that I have had 100% success with.
Remember – when you are flushing, you are trying to get rid of that buildup of nutrients. Most of that buildup is NOT above the ground. You are trying to flush the roots and soil. So try to do it at the beginning or end of the day when you can mist the plants with plain water. This will lower their transpiration and keep them from sucking up more flush water than they need. This step is not required, but its on the Clearex label so I do it.
Step 1 – Drain your res and refill. Add Clearex at about 20-30ml / Gallon. pH balance to 5.7-6.2 depending on whether you’re hydro or soil.
Step 2 – Run this mix through your plants. If you are doing containers you want to achieve significant runoff. Far more than your standard watering. The bottle calls for AT LEAST 80-90% runoff. So if you have a 5 gallon pot, you will want to put 3-6 Gallons of water through depending on how dry the soil is when you flush, and how much drainage. With a little experience with your soil you can skip the rest of the steps and call it done right there. If you really want to be sure then use the ppm measuring described below.
If you are doing hydro, saturate the system for 5-15 minutes then allow it to drain back to the res. No need to drain the res.
Step 3 – Measure the ppm of the runoff.
Step 4 – Run the same Clearex/water through again.
Step 5 – Again measure the ppm of the runoff. The ppm should be the same or higher than the first time. This is because you are sucking all those excess nutes out.
Step 6 – Keep repeating this cycle until you see little to no change on the ppm. For me this is usually two times, sometimes three.
Now drain the res again. Refill with your regularly scheduled nutes or water and let the timer do its thing.
To use the Problem-Solver, simply start at #1 below. When you think you’ve found the problem, read the Nutrients section to learn more about it. Diagnose carefully before making major changes.
1) If the problem affects only the bottom or middle of the plant go to #2. b) If it affects only the top of the plant or the growing tips, skip to #10. If the problem seems to affect the entire plant equally, skip to #6.
2) Leaves are a uniform yellow or light green; leaves die & drop; growth is slow. Leaf margins are not curled-up noticeably. >> Nitrogen(N) deficiency. b) If not, go to #3.
3) Margins of the leaves are turned up, and the tips may be twisted. Leaves are yellowing (and may turn brown), but the veins remain somewhat green. >> Magnesium (Mg) deficiency. b) If not, go to #4.
4) Leaves are browning or yellowing. Yellow, brown, or necrotic (dead) patches, especially around the edges of the leaf, which may be curled. Plant may be too tall. >> Potassium (K) deficiency. b) If not, keep reading.
5) Leaves are dark green or red/purple. Stems and petioles may have purple & red on them. Leaves may turn yellow or curl under. Leaf may drop easily. Growth may be slow and leaves may be small. >> Phosphorus(P) deficiency. b) If not, go to #6.
6) Tips of leaves are yellow, brown, or dead. Plant otherwise looks healthy & green. Stems may be soft >> Over-fertilization (especially N), over-watering, damaged roots, or insufficient soil aeration (use more sand or perlite. Occasionally due to not enough N, P, or K. b) If not, go to #7.
7) Leaves are curled under like a ram’s horn, and are dark green, gray, brown, or gold. >> Over-fertilization (too much N). b) If not, go to #8…
8) The plant is wilted, even though the soil is moist. >> Over-fertilization, soggy soil, damaged roots, disease; copper deficiency (very unlikely). b) If not, go to #9.
9) Plants won’t flower, even though they get 12 hours of darkness for over 2 weeks. >> The night period is not completely dark. Too much nitrogen. Too much pruning or cloning. b) If not, go to #10…
10) Leaves are yellow or white, but the veins are mostly green. >> Iron (Fe) deficiency. b) If not, go to #11.
11) Leaves are light green or yellow beginning at the base, while the leaf margins remain green. Necrotic spots may be between veins. Leaves are not twisted. >> Manganese (Mn) deficiency. b) If not, #12.
12) Leaves are twisted. Otherwise, pretty much like #11. >> Zinc (Zn) deficiency. b) If not, #13.
13) Leaves twist, then turn brown or die. >> The lights are too close to the plant. Rarely, a Calcium (Ca) or Boron (B) deficiency. b) If not… You may just have a weak plant.
Nitrogen – Plants need lots of N during vegging, but it’s easy to overdo it. Added too much? Flush the soil with plain water. Soluble nitrogen (especially nitrate) is the form that’s the most quickly available to the roots, while insoluble N (like urea) first needs to be broken down by microbes in the soil before the roots can absorb it. Avoid excessive ammonium nitrogen, which can interfere with other nutrients. Too much N delays flowering. Plants should be allowed to become N-deficient late in flowering for best flavor.
Magnesium – Mg-deficiency is pretty common since marijuana uses lots of it and many fertilizers don’t have enough of it. Mg-deficiency is easily fixed with Â¼ teaspoon/gallon of Epsom salts (first powdered and dissolved in some hot water) or foliar feed at Â½ teaspoon/quart. When mixing up soil, use 2 teaspoon dolomite lime per gallon of soil for Mg. Mg can get locked-up by too much Ca, Cl or ammonium nitrogen. Don’t overdo Mg or you’ll lock up other nutrients.
Potassium – Too much sodium (Na) displaces K, causing a K deficiency. Sources of high salinity are: baking soda (sodium bicarbonate “pH-up”), too much manure, and the use of water-softening filters (which should not be used). If the problem is Na, flush the soil. K can get locked up from too much Ca or ammonium nitrogen, and possibly cold weather.
Phosphorous – Some deficiency during flowering is normal, but too much shouldn’t be tolerated. Red petioles and stems are a normal, genetic characteristic for many varieties, plus it can also be a co-symptom of N, K, and Mg-deficiencies, so red stems are not a foolproof sign of P-deficiency. Too much P can lead to iron deficiency.
Iron – Fe is unavailable to plants when the pH of the water or soil is too high. If deficient, lower the pH to about 6.5 (for rockwool, about 5.7), and check that you’re not adding too much P, which can lock up Fe. Use iron that’s chelated for maximum availability. Read your fertilizer’s ingredients – chelated iron might read something like “iron EDTA”. To much Fe without adding enough P can cause a P-deficiency.
Manganese – Mn gets locked out when the pH is too high, and when there’s too much iron. Use chelated Mn.
Zinc – Also gets locked out due to high pH. Zn, Fe, and Mn deficiencies often occur together, and are usually from a high pH. Don’t overdo the micro-nutrients-lower the pH if that’s the problem so the nutrients become available. Foliar feed if the plant looks real bad. Use chelated zinc.
Check Your Water – Crusty faucets and shower heads mean your water is “hard,” usually due to too many minerals. Tap water with a TDS (total dissolved solids) level of more than around 200ppm (parts per million) is “hard” and should be looked into, especially if your plants have a chronic problem. Ask your water company for an analysis listing, which will usually list the pH, TDS, and mineral levels (as well as the pollutants, carcinogens, etc) for the tap water in your area. This is a common request, especially in this day and age, so it shouldn’t raise an eyebrow. Regular water filters will not reduce a high TDS level, but the costlier reverse-osmosis units, distillers, and de-ionizers will. A digital TDS meter (or EC = electrical conductivity meter) is an incredibly useful tool for monitoring the nutrient levels of nutrient solution, and will pay for itself before you know it. They run about $40 and up.
General Feeding Tips – Pot plants are very adaptable, but a general rule of thumb is to use more nitrogen & less phosphorous during the vegetative period, and the exact opposite during the flowering period. For the veg. period try a N:K ratio of about 10:7 :8 (which of course is the same ratio as 20:14 :16), and for flowering plants, 4:8 :8. Check the pH after adding nutrients. If you use a reservoir, keep it circulating and change it every 2 weeks.
A General Guideline for TDS Levels is as Follows:
seedlings = 50-150 ppm; unrooted clones = 100-350 ppm; small plants = 400-800 ppm; large plants = 900-1800 ppm; last week of flowering = taper off to plain water. These numbers are just a guideline, and many factors can change the actual level the plants will need. Certain nutrients are “invisible” to TDS meters, especially organics, so use TDS level only as an estimate of actual nutrient levels. When in doubt about a new fertilizer, follow the fertilizer’s directions for feeding tomatoes. Grow a few tomato or radish plants nearby for comparison.
pH – The pH of water after adding any nutrients should be around 5.9-6.5 (in rockwool, 5.5-6.1). Generally speaking, the micro-nutrients (Fe, Zn, Mn, Cu) get locked out at a high pH (alkaline) above 7.0, while the major nutrients (N, P, K, Mg) can be less available in acidic soil or water (below 5.0). Tap water is often too alkaline. Soils with lots of peat or other organic matter in them tend to get too acidic, which some dolomite lime will help fix. Soil test kits vary in accuracy, and generally the more you pay the better the accuracy. For the water, color-based pH test kits from aquarium stores are inexpensive, but inaccurate. Invest in a digital pH meter ($40-80), preferably a waterproof one. You won’t regret it.
Cold – Cold weather (below 50F/10C) can lock up phosphorous. Some
varieties, like equatorial sativas, don’t take well to cold weather. If you can keep the roots warmer, the plant will be able to take cooler temps than it otherwise could.
Heat – If the lights are too close to the plant, the tops may be curled, dry, and look burnt, mimicking a nutrient problem. Your hand should not feel hot after a minute when you hold it at the top of the plants. Raise the lights and/or aim a fan at the hot zone. Room temps should be kept under 85F (29C) — or 90F (33) if you add additional CO2.
Humidity – Thin, shriveled leaves can be from low humidity. 40-80 % is usually fine.
Mold and Fungus – Dark patchy areas on leaves and buds can be mold. Lower the humidity and increase the ventilation if mold is a problem. Remove any dead leaves, wherever they are. Keep your garden clean.
Insects – White spots on the tops of leaves can mean spider mites
Sprays – Foliar sprays can have a “magnifying glass” effect under bright lights, causing small white, yellow or burnt spots which can be confused with a nutrient problem. Some sprays can also cause chemical reactions.
Insufficient light – tall, stretching plants are usually from using the wrong kind of light.. Don’t use regular incandescent bulbs (“grow bulbs”) or halogens to grow cannabis. Invest in fluorescent lighting (good) or HID lighting (much better) which supply the high-intensity light that cannabis needs for good growth and tight buds. Even better, grow in sunlight.
Clones – yellowing leaves on unrooted clones can be from too much light, or the stem may not be firmly touching the rooting medium. Turn off any CO2 until they root. Too much fertilizer can shrivel or wilt clones – plain tap water is fine.
How does plant nutrient metabolism work?
In other words, how do plants eat?
In order to live, plants need these 16 essential elements, called macronutrients and micronutrients.
# carbon (C)
# hydrogen (H)
# oxygen (O2)
# nitrogen (N)
# phosphorus (P)
# potassium (K)
# calcium (Ca)
# magnesium (Mg)
# sulfur (S)
# Boron (B)
# Chlorine (Cl)
# copper (Cu)
# iron (Fe)
# Manganese (Mn)
# Zinc (Zn)
# Molybdenum (Mo)
Macronutrients and micronutrients
Most of the plant is formed from Hydrogen, Carbon and Oxygen (~95% of the dry mass). Carbon comes from carbon dioxide (CO2) in the air. Hydrogen and Oxygen come from water. Note that this Oxygen must be available ‘mixed in the water’, as Dissolved Oxygen.
The remaining macronutrients, Nitrogen, Phosphorus, Potassium, Calcium, Magnesium and Sulfur must be available to the plants root-hairs from the soil or from fertilizers, as part of the solution the plants roots are in contact with. Same applies to the micronutrients, Iron, Manganese, Boron, Copper, Zinc, Molybdenum and Chlorine.
These essential elements are mostly used by the plants in ionic form, as inorganic salts that have dissolved into the nutrient solution.
Next we will follow the course of an water drop with some fertilizers in it through the plant, to learn how plants metabolism works.
The solution in the root-zone
Whether plants are grown in soil, rockwool or water, solution with dissolved nutrients must come into contact with the plants roots. This nutrient solution should be of the suitable temperature, concentration, acidity and chemical composition to be healthy and to contribute positively to the plants growth and well-being.
For ‘our-favorite-plant’ temperatures should be between 16-26 C degrees, or 60-80 F degrees. Low temperatures slow down the metabolism of the plant and its growth. On the other hand, in high temperatures there will be less of Dissolved Oxygen in the solution, causing the roots to be more vulnerable to diseases and
Acidity in the root zone effects the intake of nutrient ions. Generally for hydroponic applications the recommended pH range for our favorite is between pH 5.2 and pH 6.0. If the the nutrient solution should become more acidic or alkaline then the availability of certain nutrients would decrease, making nutrients less available or even completely unavailable to the plant. Also problems like nutrient ions precipitating out of the solution could arise.
The concentration of the nutrient solution should not be too strong, ie. over 1300-1500 ppm, nor should it be too weak. A strong solution would cause negative osmotic pressure on the plant. Because of high salinity, ie. the amount of dissolved solids outside the plants root cells, water flow would reverse to flow out of the plants, causing plants to lose their turgor, to wilt. Too weak solution wouldn’t contain enough nutrients and might cause osmotic flow of nutrients to reverse, causing nutrient ions to flow out of the cells, leaving the plant hungry for more.
“If a cell is in contact with a solution of lower water concentration than its own contents, then water leaves the cell by osmosis, through the cell membrane. Water is lost first from the cytoplasm, then the vacuole through the tonoplast. The living contents of the cell contracts and eventually pulls away from the cell wall and shrinks, this is known as Plasmolysis.”
Quote from CourseworkHelp: AT1- Osmosis In potatoes.
Chemical composition of the nutrient solution is likewise important. Without certain nutrients plants cannot live, or cannot complete their life cycle. Toxic substances in the solution could cause the plant to die, or perhaps cause the grower, enjoying the fruits of his/her labors, to fall sick or die. Sufficient Dissolved oxygen levels should be present in the solution, root-cells need this to breathe, like fish, underwater. Also the essential elements should be in a such a form as to be available to the plant, as inorganic ions. With the plethora of nutrient products currently available to most growers, the nutrient composition is rarely a problem.
Rosa Root hair meets Wally Waterdrop
To simplify, plants roots are basically composed of surface cells that absorb the water and the elements, and of inner structures of veins that translocate the water & elements, called nutrient solution from here on, upwards to the stem.
The cells on the root surfaces, called root hairs because of their ‘fuzzy’ nature, can passively diffuse the nutrient solution, or expend energy and actively transport water and nutrient ions across their cell membrane.
Every organism on our planet, according to the science is composed of one or more cells. An average human might have billions of cells. On the other hand, bacteria are single celled organisms. Plants are multicelled, of course. Cells always have an cell wall, surface membrane, and internal organs.
The cell wall, often called the primary cell wall serves to protect the cell from the surrounding environment and to support the cell. The primary cell walls of plants are made of tiny cellulose fibers intertwining on the surface of the cell, pumped out by tiny cellulose rosettes moving across the surface of the cells plasma membrane right ‘beneath’ the cell wall.
“If you put a plant cell in water, water enters by Osmosis, then swells up. However, the cell will not burst. This is due to the fact that the cell walls are made from cellulose, which is extremely strong. Eventually, the cell stops swelling, and when this point is reached, we say the cell is turgid. This is important, because it makes plant stems strong and upright.”
Quote from CourseworkHelp: AT1- Osmosis In Potatoes.
The surface membrane is also called plasma-membrane or double lipid layer membrane, and the internal organs the cytoplasm. The cell membrane inside the outer primary cell wall is an complex, living tissue of biochemical wonders and little molecular machines that can move molecules back and forth across the membrane and build the cell wall. There are also little conduits between the adjacent individual cells, to make transport of water and ions even easier. These pores are called plasmodesmata.
Functions of the membrane
This plasma membrane has many functions, each function covered by particular tiny organs, made of proteins:
# Keeping the solution balance suitable in- and outside the cell. There are proteins on the membrane that can pump water and ions in and out of the cell wall. It’s also referred to with an really advanced term ‘Maintaining ionic homeostasis’. Be sure to dazzle your friends with this term.
# Signaling and sensing the environment. Such as receiving hormonal messages.
# Building the primary cell wall. Small organs moving on the membrane spewing out long strands of cellulose that form the external cell wall matrix.
# Regulating the turgidity. Adjusting the osmotic pressure.
# Communicating with the adjacent cells, through the plasmodesmata mentioned earlier.
So once an root-hair-cell starts to feel a little thirsty, or perhaps gets an message from its neighbor to move in more nitrogen, it can utilize several strategies to ‘transport’ the required molecyles from the nutrient solution, into the cell and onwards. If no energy is required upon the cells part, this is called passive transport, and, logically, if energy is expended, active transport is in progress.
Because of the physical and chemical nature of the nutrients ions, the substances dissolved in the nutrient solution, all the substances and even the solution itself are subject to osmosis, diffusion through the selectively permeable plasma membrane. This is because each molecule has an electric charge, and differing concentrations of the molecules create electric potential between the differing concentration areas, called gradients (concentration gradient, potential gradient, trans-membrane electrochemical gradient…).
What is diffusion?
In diffusion solutes (molecyles) seek to move from the stronger concentration towards the more diluted thus equalizing any possible differences in the concentration.
In other words, diffusion is the effect of molecyles dissolved in solution, diffusing from the area of higher concentration towards the area of lower concentration of dilutes.
Suppose two solutions are mixed in an container: water and pH down. Right after mixing, concentrations of pH down in the water are uneven. After a while, after diffusion, pH down will be equally concentrated across the volume of the water.
Diffusion occurs in solutions consisting of particles. The energy to diffusion is created from the random thermal motion of molecyles, also called the brownian motion.
Diffusion happens through cell walls also, except where blocked by the selectively permeable cell wall.
Diffusion through an cell wall
Anything will permeate the double lipid layer of the cell wall given enough time. However, there are large differences in the time period required.
High permeability (through cell walls)
Cl+ (Chlorine ion)
K- (Potassium anion)
NA+ (Natrium ion)
Table 1. Permeability for some substances
Higher the permeability, the faster is the movement through the cell walls into the cells.
What is Osmosis?
Well, Osmosis is actually diffusion of water with an permeable layer of some kind that’s permeable by the solution. In cell biology terms words, Osmosis is what diffusion of water through the cell wall is actually called.
To give an more practical example, Osmosis is the diffusion of water from a hypotonic solution, solution that is low in dissolved solids, into a hypertonic solution which contains higher amount of dissolved solids across and selectively permeable membrane.
Osmotic diffusion through cell walls is passive transport mechanism, because it requires no energy from the cell’s part.
As you can see above, cell walls can permeate water and some molecyles easily. However, some of the molecyles require active effort from the cells to transport into the cells. This is called active transport.
What is Reverse Osmosis?
Reverse Osmosis-term is most often used of water purification systems that use water-permeable layer to purify water. Reverse Osmosis water contains only water molecyles (H2O) or molecyles smaller than that. Reverse osmosis -layers are capable of rejecting bacteria, salts, sugars, proteins, particles and dyes among other things (molecule size smaller than ~200 daltons).
In plants the condition of Reverse Osmosis suggests that the concentration of solutes in solution outside the (root) cells is higher than inside the (root) cells and thus the direction of the water movement is out of the (root) cells, and not inwards. Simply put, the salty solution draws water from the plants, often causing plants to wilt.
The root hair cells can utilize the transport proteins and ion pumps, located on the plasma membrane, to actively move solutes across the membrane. This way plants can control the intake of water and nutrients from the solution that is in contact with the root hairs.
There is much more to the whole transport-business. To learn more about the issue, type some of these keywords into your favorite search engine: “cell wall transport active facilitated diffusion cytosis ATPase”.
Normal ‘hypertonic’ situation
Normally all plants cells are filled with water, and the whole plant is ‘rigid’ with the water. This is caused by the high positive internal osmotic pressure, also called turgor. This state of high internal pressure in cells is called hypotonic. Should a plant lose its turgor, it would wilt and its leaves would be completely limp. This opposite state would be hypertonic, ie. when a cell would have an negative internal osmotic pressure, causing water to flow out and the cell to shrink (or in case of rigid-walled cells, the interal cell membrane (plasma membrane) to shrink).
Most energy for keeping the cells hypertonic results from the transpiration, the evaporative pull resulting from water evaporated through the stomata, small openings on the lower leaf surfaces, and from the cohesion & capillary action of the water in the plants veins (xylem).
Roots control the environment and intake and exhaust of solutes Some of the pressure is created actively by the root-hair cells – cells pump water inside the plant, using their cellular energy (ATP). In similar fashion plant can actively transport nutrients, like mentioned above.
Note that the above is simply one theory to explain the phenomena that happens in plants and cells. There are different theories on how cell-walls, diffusion etc work. For more info on this theory, do an web search with ‘Donnan equilibria’.
Roots are responsible for extracting water and the nutrient minerals from the growing medium. The root tip, also called apical meristem grows into the medium, pushing through it covered by the root cap, an protective shield of cells.
On the roots surface layer, the epidermis, root hairs have developed on top of the cortex, which in turn is formed around the internal layer of the roots, also called the endodermis. Root hairs have large surface area which effectively absorbs nutrients from the medium. Symbiotic, mycorrhizal fungi can also increase the surface area, greatly enhancing the intake of nutrients.
Root hairs cover the mature root surface. They are tiny hair-like structures that grow right into the medium and increase the surface area of the root to asphyxiating numbers. There can be more than 20000 root hairs on an area equal to fingernail. On the average length of 5 mm, the surface area of these root hairs would exceed 1/3 square meter, over 3 square feet!!!(h=0,005m, r=0,0005m) So thanks to this huge surface area, roots can supply water and nutrients to an very large plant.
Root hairs are often visible by the naked eye. Root hairs are quite short lived and often mature roots have no visible root hairs.
Nutrient movement across membranes
The nutrients, minerals dissolved into water-solution, are transported as ions. Ions are soluble in water but cannot cross membranes without the presence of transport proteins, little organs on the surface of the membrane. The transport of the negatively charged ions requires the transport of an positively charged particle in the opposite direction. These positively charged particles are protons, H+ – hydrogen without an electron. This way the electric potential and chemical potential stays in equilibria, with equal electric potentials on both sides of the membrane. These protons are pumped actively across the membrane using ATP, adenosine triphosphate, as an energy source.
There are basically three mechanisms that transport the nutrient ionsrimary and secondary ion pumps and ion channels. These are proteins that sit in the plasma membrane, each type specific to the nutrients they carry.
Some of the ion pumps move the H+ protons out of the cell, an some into the cell. These are known as primary ion pumps. This movement of H+ changes the potential/gradient, and facilitates the movement of the other ions. There are also the secondary ion pumps that move the other ions in and out of the cell.
Finally there are the ion channels, little channels with opening and closing ‘gates’ that permit the nutrient ions to move across the membranes, driven by the potential & electrochemical gradient.
Movement of nutrient solution inside the plant
Once the water and the nutrient ions have been absorbed by the root hair-cells, these are transported across the cell plasma membranes, directly in the cells, symplastically, or between the cells, in intracellular spaces, apoplastically.
Once the solution has traveled through the root-hairs and the cortex, into the inner parts of the roots (endodermis), it can only travel into the vascular system inside the cells, symplastically, transported through the membranes, in the cells. In the vascular system, the bundles of veins, there are two types of veins – the xylem, and the phloem. A these vascular bundles are basically vertical veins running from the roots to the growing tip.
The bulk of the flow is created by the transpiration pull, drawing the solution upwards, towards the leaves. Diffusion and active transport also help in the movement of the solution. The physical properties of water, cohesion ie. the attraction of water molecules to one another and the resulting capillary action also helps in creating the strong vertical upward movement of water. This is an very efficient system – plants can move large volumes of nutrient solution from the roots up to the foliage often very high above the root level.
The vascular bundles run throughout the plants, in the stems and the leaves. You can actually see the bundles in the leaves – the veins of the leaves. Once aboard the ‘plants internal transport system’, the solution is moved around the plant, and the nutrients used for building blocks, to create energy in the photosynthetic process, and to regulate the metabolism and the turgidity of the plant.
Most of the water is transported into leaves, where it is evaporated through small openings on the lower surfaces of leaves. These openings are called stomata (singular stoma). Plants can open and close these to control the amount of evaporation. As water evaporates, it contributes to the total transpiration pull. In nature the evaporated water floats in the air, condenses into clouds, rains down on the plants and the cycle is completed.
How does all this apply to Cannabis -plants?
So how do the plants roots, or the roothairs in them, control the nutrient intake?!? Wouldn’t any and all nutrient ions diffuse themselves all around the plant and the nutrient solution (as opposed to Nitrogen going to leaves and Kalium to the stems)?!?
With active transport-mechanisms root cells can ‘select’ the ions (and other substances) that are transported into the cell. This way they can adjust (to) the environment, and actually even work against the osmotic imbalance. Looking at the larger context, plants use the energy from photosynthesis to keep the juices flowing in the right places.
“Excessive flow of water into a cell by osmosis can burst the cell. Cells protect against this using processes of osmoregulation. If external pressure is applied to the stronger solution, osmosis is arrested. By this mechanism plant cells can osmoregulate, since the cell wall of a fully turgid cell exerts pressure on the solution within the cell.” Quote from CourseworkHelp: AT1- Osmosis In Potatoes.
Nutrient solution and soil management
So once an grower understands these principles (s)he can apply these to practice. Its easy to understand that strong changes in the amount of dissolved substances in the root-zone would stress the roots by changing the direction of the osmotic flow. A plant could suddenly experience strong stress, and possibly even direct physical damage to the roots.
For each plant there exists an optimal environment. By measuring the pH, TDS or EC one can understand the conditions in the root-zone and act accordingly. The suitable range was discussed in the second paragraph of this text, The solution in the root-zone.
DISCLAIMER: Information in this text may not be completely correct. This text is meant as an starting point for further study.
Do I need to run my CO2 equipment when my lights are off?
No. The plants only use Co2 when in the process of photosynthesis (when the lights are turned on).
I have a CO2 regulator that freezes up on me. What is wrong with it & how do I fix it?
When this occurs, check the O-ring where the regulator attaches to the bottle, you may need a new one.
I use a CO2 generator & I have the equipment off at night but, the CO2 level keeps building up at night, why?
There is a pilot light on the Co2 generators that uses natural gas or propane, this is the most likely cause. Check your timer to ensure it is set correctly.
What CO2 level do Clones need?
Clones need a Co2 range of 300-400 PPM.
What CO2 level do moms need?
Moms only need a CO2 level of around 300-400 PPM
What is the best way to control the CO2 level in my grow room?
A digital Co2 controller ensures the best reading and results. If you decide to go the Co2 route, it is worth spending the extra money and getting a reliable controller.
What is the best way to provide the plants with CO2 using a tank & regulator?
Co2 drops to the floor so mixing it with the air is key. One of the best ways to ensure the Co2 is being mixed properly is by attaching the Co2 feed lines to your oscillating fan, Air Handler or Inline fan used for “Scrubbing” the room.
What is the normal CO2 level outside?
The natural Co2 level outside is 300-400 PPM.
What level of CO2 is best for my garden?
If you are in the beginning growth stage a Co2 level between 300-400 PPM is perfect. If you are in the advanced growth stage up to 800 PPM is a good range. If you are in the flowering stage a range of 900-1200 PPM is ideal. When your PPM increases above 15000, your plants become starved of oxygen.