Ask The Doc goes over some CAUSES and CURES for YELLOW LEAVES on your plants! Here the good Doctor discusses yellowing leaves using a Pumpkin Plant as a visual guide.

TO PURCHASE FERTILIZER: /categories/nutrients

In this episode of HTGSupply’s Ask the Doc, Dr. Myers goes over the effectiveness of Phosphorus in your garden. He touches on how to get your seeds started with Phosphorus and maintaining your garden throughout the season with high-phosphorus fertilizers. Doc explains how using phosphorus should be step one on knocking out any diseases in your garden. Take these tips from Doc, and put them to use in your next garden. Good Growing!

Welcome to another episode of HTG Supply’s “Ask the Doc”. This time around, Dr. Myers goes over the uses and benefits of Perlite in your indoor or outdoor garden. Perlite is made from an all-natural volcanic glass so it is an excellent soil amendment for organic soil gardens. Its porous and light-weight properties make it perfect for oxygenating and lightening your soil, whether you’re growing inside in containers like smart pots or outdoors in raised garden beds. Oxygen in your soil is just as key as water for the health and growth of your plants—take it from the Doc! Good Growing!

 

TO PURCHASE STUMP TEA VEG BOOST: /categories/nutrients/stump-tea

In this episode of HTGSupply’s Ask the Doc, Dr. Myers goes over the effectiveness of Nitrogen in your garden. He touches on how to ease Nitrogen into your growing regimen; not too early, and not too late. Nitrogen has it’s place, time, and need during your season of growing. Take these tips from Doc, and put them to use in your next garden. Good Growing!

Ask The Doc explains how to clone plants using hormones and an HTG Supply Cloning Bucket! In the video he will compare the root growth of the Cloning Bucket versus the use of Starter Plugs in a Tray. HTG SUPPLY’s Ask The Doc can be reached by going to www.htgsupply.com and clicking on the “Ask The Doc” link on the homepage. Ask the Doc has a PhD in plant biology and is here to help you become a better grower!

Ask The Doc: What Is Coco Coir (And How Do I Use It?)

 

I’d like to talk to you a little bit about a product called coco coir. Now coco coir has at least two uses in gardening, you can use it as a hydroponic medium or you can use it as a soil amendment.You can add it to the soil, and before we get into that what is it?

Well, coco coir is actually comes from coconuts and some coconuts are harvested they have the hard outer shell, then we have the stuff in the middle the liquid and the coconut meat if you will, that were eaten, then all that stuff in between the outer shell and the meat liquid in the middle that’s the coir. Now for many many years this was a waste product. Companies didn’t know what to do with it and so there was literally mountains of this cocoa coir just piled up in the tropics where the coconuts are harvested. Then people began to use the fibers for various things. You can use them for doormats and some plant holders, but in gardening as I said it’s a great hydroponics medium and it’s also a very good soil amendment. Now when they harvest the coir what they do is, they take the parts- they use the meat to sell it -then they’re gonna soak the coir in water and they’re gonna let it dry for almost a year – then after a year it’s compressed greatly so it’s easier to ship and move around then it’s sent to you. Now as a hydroponic medium it’s a very good one to start off with it’s sort of forgiving and it’ll look much like you’re growing in dirt. You’re gonna have plants and pots but they’re gonna be growing in coir. Coir has no nutrients though so this truly is a hydroponic system so you’re gonna have to provide all the nutrients to your plant as you’re watering or as a soil amendment it is great because it increases the porosity of your soil. What that means it’s gonna increase the pore space in your soil this means water and the roots will be able to move easier through the soil and you have fast growing roots you’ll have a fast growing plant.

Coco coir also absorbs water up to ten times its own weight in water so this means that by adding this to the soil you’re going to have more pore space so that the roots and water coming through it but it’s also they’re gonna have water available. If the plants will ever run out of water it’s also a good product to use outdoors because if you have a clay soil it increase the porosities allowing the roots to move through it if you have a sandy soil. The water holding capacity will mean that it won’t dehydrate. So you can add this to any outdoor soil to improve the soil. Well now coco coir is very similar to peat moss and if you pay attention many top quality soils make it, that you buy, has a few possible so it’s a very good product to add as an amendment. However coco coir is a much better product and I’ll tell you why -#1- this is a sustainable product. Peat moss, however is actually mined from peat bogs and these can take decades or more often centuries for this piece to form it’s not sustainable. At harvest at a coconut takes about two months to grow so every two months we can get a new one. Also the pH of the coco coir is not as low as it is in peat moss. Peat moss to have a ph as low as 3.8 up to 4.5. You really need to raise that up to almost 6. Now Coco coir is a pH of about 5 to 5.5 so you don’t have to worry about raising as much as no product is perfect and that is one of the problems with coir. Is it does have a pH a little less than you want you have to raise the pH a little bit not as much as you want.

People also use Coco coir and you have calcium or magnesium deficiencies and that’s very easy to fix all you do that counts zero magnesium and most growers are go through that anyway. But if you’re growing in coir make sure you also get a calcium magnesium supplement. Now I have some samples here you can see. Here is a little bit of the dry Coco coir outcomes you can see some of the fibers in there and a little bit of coir. Here I have added some water. This was the same amount but you see there’s much more in here because it expands and very much like soil you can see when it’s dry it’s a little bit lighter when it’s wet darker. Now when you’re going to order or buy the coir at the HTG Supply store you’re gonna get a large brick of it and I have that here. So here we have a very large brick of coir. Very compressed. Very hard. Now a few years ago when you got this you would have to put this in a wheelbarrow or a large five-gallon bucket and soaked in water but how they ship it today very clever is they ship it in this little plastic bag and so when you get this bag you simply open up the bag and you’re gonna pour the water inside of here and then over an hour so this will swell up and then you’re ready to use the coconut coir. So I really love this as a soil amendment as I said you can add about 40% of material growing in. Coco coir water it increases porosity so your roots are going to grow better. Water is going to move better through your soil. It holds onto water so if none of your roots are gonna dry out and die and it is sustainable so this is a great product you never tried it go ahead and give it a try it’s not that expensive easy to use.

This article is part of a series written for HTGSupply by plant biologist Dr. E.R. Myers.

1. What is plant propagation
2. Types of cuttings
3. Cuttings overview
4. Cutting supplies
5. Preparation
6. General technique
7. Rooting Compounds
8. Rock wool Vs bio plugs and rooting agents

What is plant propagation

There are several methods of getting new plants or “propagating” plants. Sexual reproduction involves mixing the pollen from a male flower with the egg of a female flower. The pollen and egg can come from one plant (selfing) or two plants (outcrossing). Either way you are mixing DNA and will get long term storage of that “new” DNA in seeds or spores.

Sexual reproduction is the only way to get improved traits but also risks mixing good traits with inferior ones. (Look for future articles on plant breeding. I welcome questions about plant breeding at askthedoctor@htgsupply.com this is one of my favorite topics since earning a Ph.D. in Plant Breeding and Genetics.)

The focus of this article is propagation via asexual reproduction such as taking cuttings of stems or leaves to create many genetically identical plants from the original (mother) plant. Another type of asexual reproduction is tissue culture, which involves growing cells from the mother plant in a nutrient agar medium. Although tissue culture kits are available to the home hobbyist, this article will concentrate on the simpler more popular methods of stem, root and leaf cutting propagation.

Asexual reproduction (sometimes called cloning) results in the offspring having the exact same genetic makeup as the original plant (mother plant). Asexual propagation is an invaluable tool used for many commercial greenhouse crops, allowing for consistent and predictable plants on a massive scale. Cloning allows growers of plants with separate male and female plants (dioecious) to grow only the number of plants needed because the clones will have the same sex as the mother plant. Clones from a genetically superior mother plant will all be just as genetically superior. An entire garden of cloned plants means all the plants will have the same growth habits, maturation time, nutrient requirements and even taste. Most plants have the ability to sprout roots when leaves or branches are cut and placed in a medium. Depending on the type of plant, each mother could produce tens, or even hundreds of identical offspring every couple of months.

Types of cuttings

One should use the type of cutting that has the most chance of success with the particular plant species they are propagating. Many nonflowering parts of a plant can be used. The most common methods are root cuttings, leaf cuttings and stem cuttings.

Root Cuttings

 This is most successful with herbs and other plants that send up new growth from roots. A section of root is removed from the mother plant and buried just below the soil surface. Eventually the root produces new shoots. Bulbs can be propagated by removing small bulblets or offsets that form at the base of the parent bulb. These small bulbs take 2 or 3 years to mature into plants that flower. For plants with more widespread root systems you basically dig up a part of the root and plant it. Pick larger roots ½ cm- 1 cm (¼ to ½ inch) in diameter near the crown of the plant. Cut them into 5cm (two inch) sections cutting off slender branch roots. Place the root cutting in a moist medium and place more medium on top, just enough to cover the root. Then treat as any other cutting, keep warm and moist and under diffused light (fluorescent lights work well). The new growth can take a few weeks to come up.

Leaf Cuttings

 Any plant with leaves such as the African violet, geranium etc. can be propagated with leaf cuttings. A leaf is removed and placed in moist soil. These have to develop both new stems and new roots. Some leaves will produce one plant at the base of the leaf. In some species, multiple new plants can be produced at many places on one leaf; this usually involves cutting the leaf veins in specific ways. You will have to try to see if it works for your plant. Using a sharp knife, cut off a healthy leaf at the point where it joins the stem. Insert the cut part, called a petiole, into the rooting hormone.

Place the end into a small container of light potting soil in which you make a small hole with a pencil. Treat as any other cutting; keep warm and moist place it under diffuse light (fluorescent light ).

Stem cuttings

This is best for plants that have a branching habit with multiple leaves per branch. A stem with a couple leaves is cut and the lowest leaves are removed and the leaf scar / node where the leaf was cut from is placed below the soil line to promote root growth from the leaf scar. If you are only taking a few cuttings, just use the end of the branch. If you want more cuttings, you can cut a single stem into multiple sections, making sure each section has leaves remaining and an exposed leaf scar. Stem cuttings produce roots usually at the node. If you use rooting hormone, be sure to put the hormone at the leaf scar.

For stem cuttings each cutting should include a couple leaves and 2-4 inches of stem. The end of the stem works best, but you can get multiple plants from longer stems with multiple nodes. As you take your clippings, dip the cut end in a rooting compound to increase rooting before putting the cutting (cut end down) in soil or growth medium, insert the stem, so that the leaf scar is below the rooting medium and the lowest leaf is just above it. I have read that re-cutting the stem on an angle immediately before placing it into the rooting compound and medium will improve success. You should definitely re-cut the stem if there is a lot of time between taking the cutting and placing it in the growth medium. The idea is that the veins that transport water (xylem) will have air bubbles after being exposed by the cut, and won’t transport water. If you re-cut the stem the xylem above the original cut will still be filled with water and will be able to transport water from the medium into the new plant. When planting the cutting, making a hole prior to planting assures that the rooting hormone will not be brushed off the cutting when you plant it.

Cuttings overview

Taking a cutting is a simple process where a small amount of the parent plant is removed and is then encouraged to grow as an independent plant. However, the practice of taking cuttings is not as straightforward/easy as it may appear. Without providing the right growing conditions, it is more likely than not that the cutting will not “catch on” (form a new plant).

Before taking a cutting it is important to keep in mind the plants life cycle. Plants that are flowering tend to have less success with cutting. Cuttings can be taken pretty much anytime the plant is growing vegetatively. For the most part, once a plant has substantially entered the flowering part of its life cycle cuttings will be increasingly less successful as different hormones come into play. The problem is that often the fruit or flower is what we want to select for when we pick our next generation of plants so if you wait to see the flowers/fruits quality, it’s too late to take clones. You can always try to take cuttings later in the flowering cycle, plants don’t read books so sometimes things work when a book says it should not. Several compounds may be used to promote the formation of roots , many contain plant hormones (auxins). Among the commonly used hormone is indole-3-butyric acid, or IBA, used as a powder, solution or gel. This compound is applied either to the cut tip of the cutting or as a foliar spray.

Cutting supplies

Sterile/ sharp cutting tool
Moist growth medium
Hand sprayer
Dome / high humidity
Rooting agent
Root warmer (heat mat)
Fluorescent lights
Nursery Tray(s)

Preparation You should have a few things on hand before you take your first cutting. You need a good sharp cutting devise like a razor blade or scalpel. You can and should sterilize your cutting tools with alcohol, fire or bleach. Before you go hacking into the plant, you need to know that the quicker you turn the cut stem/leaf/root into a plantlet the better your success rate. In other words, as soon as you cut you should place the piece of plant in the medium and cutting environment. This means the growth medium has to be ready. I provide the cutting with a good growth medium such as rockwool, biodegradable starter pellets or soil that is light/airy. Perlite, vermiculite, and/or water-soaked sphagnum moss can be added to potting soil to make the soil light.

General Technique. Because the cuttings don’t have roots, water is going to be a limiting factor. Once you have planted the number of cuttings you want, cover them with a clear plastic dome (like a tall Humidity Dome ) to retain humidity and give the plants 18 hours of diffused light per day. With all types of cuttings you need to provide a humid environment which generally means placing the cuttings where the air can be kept humid/moist but still allow light to get to the plants. The light you use should be limited light, remember light drives photosynthesis which requires water. If you give the plants a lot of light, they will use up what water they have and dehydrate. Fluorescent lights are perhaps the best suited light source for cuttings. The light output promotes good growth, the light intensity is not excessive, and the low temperature does not put heat stress on the tender plantlets. Keep the light cycle on mostly light (18 hours on 6 hours off per day for example) and keep the fluorescent light several inches above the plants.

Keep the cuttings moist by generously and thoroughly using a fine mister (spray bottle). I use a inexpensive hand sprayer and there are many different styles for sale including rechargeable electric and pressurized sprayers available at HTGSupply.com. After taking the cutting, dipping it into rooting hormone and putting it in a moist medium, you should gently mist the plants until most of the leaf surface is covered with tiny water droplets. Then place a clear dome over the plants and put them under a fluorescent light. After a day the plant leaves should be dry. There is no need to mist if the leaves aren’t dry but if they are, please mist again. You also definitely need to get some more air flow over your cuttings before misting again. Your humidity dome should have some air vents that will need to be opened a little to provide some air flow. If you keep the cuttings’ environment too wet you are likely to get fungal growth, not plant growth. You could also mist the growth medium to keep it moist but not wet. Be gentle in your hand misting, you don’t want to stress the cuttings or worse knock them over with a blast of water. You should also place a heating mat underneath your cuttings. If you are using a Nursery Tray, the tall Humidity Dome is made so fit over top of the tray and heat mats are made to fit underneath the tray(s). To fine tune your cuttings medium temperature you may also get a Heat Mat Thermostat which adjusts the heat making the process more exact and possibly more successful. Having the roots warm and the above air temperature cool will greatly improve your success.

The two biggest threats to your cuttings, once they are established in the growth medium is stem rot and dehydration. Dehydration comes from improper irrigation i.e. forgetfulness. You must remember that cuttings are fragile little “babies” that need your daily attention. Please remember to keep an eye on them and make sure the grow medium is moist and your humidity levels in check. Stem rot is from a lack of oxygen around the plants. This can be prevented if you remove the cover for several minutes each day (up to an hour) to give the plants fresh air (oxygen). Even if you sterilize the area to prevent fungus and bacterial growth, if there is a lack of oxygen, carbon is also going to be limited which will give you a poor chance of plant survival (See Carbon and ventilation 9/08 ). Removing the dome for airflow is therefore bad for fungus and good for the plants so it should be done everyday for all types of cuttings. You should increase the time the dome is off the plants each day after the first few days. After a week to 2 weeks you should be able to remove the dome completely. If you notice the cuttings leaves “drooping” it is time to replace the humidity dome.

When the cuttings perk up and you see new growth you know the clippings have rooted, give the stems a very gentle tug. If the stem stays in the medium, success! Another method is to pick up the cutting by the medium (starter plugs ) to see if roots are growing out of the grow medium. The cuttings/clones should be transplanted soon after rooting. Transplant the new emerging plant into the area for vegetative growth. Continue to mist the plants to keep a humid environment for about 2 more weeks until active growth begins. As with anything you should start more cuttings than you need because it is likely that not all will make it and some will have stronger root masses than others. You will most likely improve in cutting success once you try it a few times.

Rockwool vs. bio plugs and rooting agents

This summer I conducted an unscientific exercise comparing various mediums and rooting agents. I did this to get an understanding of various products and to get pictures to help explain the process. I do not want to give the impression that what I am writing about is a valid scientific experiment, it is not. The following is an exercise in taking cuttings. My experience with cuttings is on a minor scale usually taking a few cutting from a “mother plant” in order to propagate plants that won’t flower or don’t breed true in the various greenhouses I have worked at.

I would welcome any ideas or comments from people that have other experiences with cuttings. As always you can E-mail me at askthedoctor@htgsupply.com This summer I worked with stem cuttings. I dipped the cut stem into the rooting compound. I used a foliar spray with tap water to maintain humidity in the cutting container. As mentioned, a rooting hormone may be used to facilitate cuttings catching on, but generally is not the most important factor in the process. Temperature and humidity are two factors that are more critical to cutting success. Some people have found that using honey makes an effective rooting compound as well as any hormone. (Humboldt Nutrients Honey Hydro Carbs and Honey Organic ES also may help with cutting success ). In general, when starting a new plant from a leaf or stem cutting, the cutting will be more likely to form roots and create a new plant if a
rooting hormone is used and some plants cannot be cloned consistently without rooting
hormones.

Hormex vs. Rootech vs Humbolt Roots vs. Clonex

ROCKWOOL all these are promoted to enhance root growth so I did a very small test to compare them. Hormex, Humbolt Roots and Clonex (small sample came with HOT HOUSE tray I purchased) are in liquid form. Rootech is a gel and a gel should stick to the stem better than a liquid or a powder. Humbolt Roots suggested that the compound be used when watering the plants. I did NOT follow directions and used Humbolt Roots as I did the other rooting agents, I simply immersed the cuttings in the liquid for a few moments before planting. I took three cuttings of lavender and hops with each product and used rockwool as the medium for all of them. All were placed in the same container with same environmental conditions. Hormex success was 2/3 lavender 1/3 hops, Clonex 1/3
lavender 0/3 hops, Humboldt roots 2/3 hops/ 3/3 lavander* and Rootech 1/3 lavander 0/3 hops. * The roots for Humboldt Roots were not well developed at two weeks, but did eventually develop, all other rooting agents at two weeks either had significant root growth i.e. could be transplanted or had no root growth.

Hormex vs. Rootech vs Humbolt Roots vs. Clonex Boidegradable Pellets

I took three cuttings of lavender and hops with each product and used biodegradable pellets as the medium. Rootexh 2/3 hops 1/3 lavender, Humboldt roots 0/3 lavander 2/3 hops, clonex 0/3 lavender 2/3 hops, hormex 2/3 hops 0/3 lavander.

I think the big difference here was not in the rooting agents but in the medium. The biodegradable pellets held much more water than the rockwool. Consequently, I realize it is a bad idea to use both mediums in one tray, the rockwool will either be too dry, or the pellets too wet. The lavender did not like the biodegradable pellets or it would be more accurate to say lavender did not like how wet I had to keep the pellets so that the rockwool would not dry out.

Lesson learned! For the remaining experiments I only used one type of medium in each tray. Hormex vs. Rootech These products both have plant hormones so I compared these two on more cuttings. I had one tray filled with 24 coconut husk pots with a potting soil mix, I put two cuttings in each pot. For the Hormex lavender cuttings 17/18 were successfully transplanted and the Rootex was 14/20 transplanted (nontransplanted = no new plant from cutting).

I only had limited space this summer but I did some other tests. I took six cuttings of spearmint and put them in rockwool using Hormex and Rootech. Both products were 3/3 but the Hormex had significant root growth after one week, the Rootech had minimal growth. I then did another comparison using lavender in rockwool both hormex and rootech were 8/8 but Hormex had 2
times the leaf and root mass as Rootech after two weeks. With this small sample, I would say Hormex is by far the better product, and is cheaper too.

Rockwool Vs Bio plugs wrap-up Ease of use, Rockwool A+ok and Bioplugs (compressed coco plugs that come with the HOT HOUSE ). Both could be used successfully for taking cuttings.

Both should be presoaked before you pick up the scissors to take a cutting. The bioplugs can be crumbly and messy and really stay saturated with water. Rockwool is neat, easy to use and had
good drainage of water.

I should note that the biodegradable plugs were soaked in plain water until they swelled, about ½ hour. Then plugs and dry rockwool were soaked overnight in diluted fertilizer (2ml/gallon Humboldt Grow 3-1-3 and 2ml/ gal Humboldt bloom 0-10-0.) I assumed this mix gives cuttings all essential nutrients, with the highest nutrient being phosphorus to promote root growth. Many people have suggested not giving cuttings any fertilizer. I used a very diluted fertilizer in this exercise. I hope this information helps and inspires you to try taking your own cuttings and to run your own experiments so that you can improve how you grow your favorite plants.

Good Growing,
Dr. E.R.Myers

This article is part of a series written for HTGSupply by plant biologist Dr. E.R. Myers.

This is the sixth of a multi-part series on plant growth and liming factors (view other articles in this series ). This month I will discuss carbon and ventilation and next month will conclude the limiting factors series with temperature and water.

As you know, the most important thing when considering plant growth is understanding limiting
factors. Plant growth is determined by limiting factors, plants that don’t receive enough of any one (1)
factor won’t grow at the maximum rate no matter how much of any other factor you give them. To grow better, find your limiting factor which will increase growth, sometimes dramatically, without having to adjust or do anything else. There are several major factors that can limit plant growth, in order of importance they are, light, water, temperature, carbon dioxide and nutrients.

1. Carbon dioxide uptake
2. Airflow to increase CO2
3. Other affects of airflow on plants
4. Carbon dioxide supplementation indoors
5. How much CO2 to add to your grow room

Carbon dioxide uptake
Light Energy + 6CO2 + 6H20 —> C6H1206 + 6 02

Concerning plant growth, everyone thinks about light and the amount of water, but an invisible, colorless odorless gas is often overlooked, even though it is of the utmost importance to good growth, and is so easy to add to an indoor garden. From previous articles you know carbon dioxide (CO2) is needed for plants to conduct photosynthesis.

Carbon dioxide diffuses (moves) into the plant via tiny holes/pores called stomata. Diffusion is a passive process meaning the plants can only get as much CO2 as there is in their immediate environment.

Stomata must be open for CO2 to get into the plant. Stomata open and close based on plant physiology and in response to environmental factors. If something keeps the stomata closed, the rate of photosynthesis will slow and eventually stop as CO2 becomes limiting. Indoor growers should know that dust or other particulate matter may clog stomata. It might be a good idea to occasionally (monthly or more if there is smoke or dust in the room) mist your plants with water on the top and bottom of the leaves (especially the bottom of leaves where in many plants the majority of stomata are located). Use enough mist so that the water beads up and runs off the leaves. The mist, like rain will wash off the leaf surface and clean out the stomata. This should be done during vegetative growth. If you are producing fruit/flowers that are susceptible to mold, you should not mist the plants once flowers begin to develop.

High humidity and misting plants can lead to powdery mildew or other fungal infections. You should mist the plants in the beginning of the light cycle so that the light will help dry the plant leaves. I am sure you know water and electricity don’t mix. BE SURE NOT TO GET ANY MIST OR WATER ON AN H.I.D. LIGHT BULB (ie: MH Metal Halide or HPS High Pressure Sodium bulbs) as it may cause the bulb to crack or break.

Although you can’t see individual stomata with the naked eye, most plants, when you look closely have tiny “hairs” on their stems and/or leaves. These protuberances are to trap air around the plant and create a microenvironment trapped air is usually warmer and has more humidity than the surrounding air. In the natural environment this microenvironment is replenished periodically with wind. Without air movement as the plant uses up the CO2 from this microenvironment CO2 can easily become limited. If the air around the plant is not moving, the growth rate will slow with limited CO2. I recommend using some type of circulation fan to move air around the plants .

Airflow to increase CO2
Carbon dioxide availability can first be increased indoors via air flow, so buy a fan before a CO2 tank. Adding light airflow will increase CO2 input and may increase H2O output so hydroponics growers should pay extra attention to the reservoir when adding a fan to the grow area.

Experienced growers know that CO2 can still be limiting even with a fan. Increasing the amount of CO2
with a CO2 release system can result in big yields when used properly (see below)

If you use an HID like many do, you should move the air around the bulb and plants with a fan and/or ventilate your grow area to remove heat. All the greenhouses I have worked in have had ventilation or air exchanges with the outside. Ventilation was needed to remove the heat and moisture coming from the lights and plants. Since ventilation can supply fresh CO2 it seems like a good idea, and it can be. However, keep in mind that if you bring in air from the outside, or even pump hot air outside, you risk getting pests into your garden, which can bring disaster. (look for future articles on pests). You should always screen air intake and exhaust if you are venting to the outside. I use a carbon filter fan combo ( see: Carbon Filters ) to move the air around the room; I direct the outflow air via flexible duct across the bulb and the top of the plants. Doing this keeps the plants safe from the heat of my HID bulb, increases the CO2 via airflow and also keeps mold spore numbers down. A carbon filter could also greatly reduce pollen, so if you are growing fruits which need pollination, or do not want pollen in the room, keep that in mind.

Concerning airflow, like any factor you need to keep in mind that too much of a good thing, is not good. You can over stress your plants with wind. Your plants should jiggle in the wind, not be blown over. You can also limit the time the wind (fan) is affecting the plants with a timer. Using a fan to simulate a slight breeze will help increase CO2 and O2 exchange, which will increase your plants photosynthesis rate and yield. I’ve seen some plants placed too close to circulation fans that have suffered “wind burn whereas the leaves of the plants were damaged by the excessive air flow.

Other affects of airflow on plants
Plants grown outdoors develop thick sturdy stems due to environmental stress. Wind causes tiny tears on the stem which are repaired, making the stem stronger. It is the same basic idea behind lifting weights to build bigger muscles. Indoor plants benefit from a lack of most environmental stresses, but not having to cope with wind stress results in weak stems.

Thigmomorphogenesis (10 cent word eh!) is the term for a stress response to mechanical stimulation that causes most plants to have increased radial stem growth (thicker stems). This mechanical stress can be shaking the plants, or simply having a fan gently blow on the plants. This stress promotes thicker stems and shortened plants. In the wild, being shorter and thick stemmed makes the plants sturdier so they can better stand up to wind. Thus, Thigmomorphogenesis has a beneficial effect, it results in shorter thick stemmed plants, the opposite effect of HPS (yellow/red) lights and high temperatures. I always put a small circulation fan on young seedlings to promote sturdy stems. This helps them hold up the big flowers later in life.

Carbon dioxide supplementation indoors
CO2 is often limiting before nutrients. Almost everyone spends thoughts and money on nutrients, consider a CO2 tank. (see: CO2 Systems ) If you ventilate your grow area, only vent your room if your CO2 system is off and make sure you let the plants sit in the CO2 for a while. There are many different environmental controllers that turn CO2 on or off with the ventilation system and some that even measure in CO2 the air and regulate the release of CO2. (see: Environmental Controls). In larger areas, you could use a carbon filter to keep down the fungal spores and bacteria, and you might not need to ventilate the area resulting in a self contained high CO2 room.

One concern would be the build up of humidity so even rooms with CO2 may need ventilated to some degree. Normal atmospheric CO2 levels (in the air) are between 300 to 500 ppm (parts per million), depending on where you live (urban or rural) with an average of 387 ppm. The earth’s atmosphere contained more CO2 when plants evolved, and plants have not lost their ability to process CO2 at higher rates. In other words, plants with ample light and water will grow faster with higher CO2 in the atmosphere. The amount of CO2 in the atmosphere for maximum plant growth is around 1500-2000 ppm. You should add additional CO2 to increase your growing areas PPM to these levels, keeping these levels can be easy with a Digital Controller. CO2 is heavier than air, and is cooler, so it should always be released above the plants. If you let CO2 go at the soil level, it may just seep out of your room and be unavailable to your plants. The best way to distribute CO2 is directly to each plant with a hose. With a tank and multiple hoses you can have a hose positioned above each individual plant.

If you have one hose, you can string it above the plants and put small holes in the tubing so the CO2 seeps out over all the plants. Keep in mind if you make big holes all the CO2 will be exhausted before it gets to the end of the tube. An easier but LESS EFFICIENT possibility is that you can put a single hose behind a fan and spread the CO2 over the area the fan blows. If you do this, you should seal your grow area with caulk in the corners and weather stripping around the doors. The faster the CO2 escapes the grow area the less effective it will be.

I have heard of a lot of kooky ways to add CO2 to your grow room, from composting in the grow area, to brewing beer (using yeast) in the grow room to exhausting a gas dryer into a grow room. I understand the desire to use organic or recycled CO2 and honestly any increase in CO2 should increase you plant growth rate. There are products on the market which natural gas or propane in order to release CO2 (See: Environmental Controls). You could even use a gas or kerosene space heater in your grow area if heat is not a problem. Please be careful to not create any fire hazards by doing so. Burning fossil fuels does release CO2 and water vapor as part of the combustion process. On average, one pound of fuel will produce about 3 pounds of CO2 and 1.5 pounds of water.

View CO2 Regulator And Tank Combo
View CO2 Regulator & Tank Combo
Good heaters should not produce any residue or carbon monoxide (CO) which is a deadly gas. It is the CO in car exhaust that kills people. If you use a fossil fuel heater to add CO2 you should vent the room before you go in to be safe. There are other natural ways to produce CO2 in your garden as well. While I have not used products like CO2 boost (which basically brews sugar and yeast to produce CO2) I believe they will add CO2 but I do not know how long the shelf life is when the CO2 will be generated. Any increase in CO2 can be beneficial, but you need to add it above the plants, most efficiently with a hose.

I would suggest you use a CO2 tank with a CO2 regulator and release the proper amount into your room at the proper time. I think that for ease, safety and efficiency having a CO2 tank with a regulator is the way to go.

How much CO2 to add to your grow room
When you advance to using a CO2 tank with timer and valve, you can regulate the amount of CO2 that you have in your grow room. If you increase the amount of CO2 to 0.2% of your rooms atmosphere, that is 2000 ppm. The first thing you need to do is figure out how much CO2 you need to release to bring your grow room to 2000 ppm. To do this determine the volume of your room (length x width x height). You then multiply your room volume by 0.002 (that is 0.2%: if you want 1500 ppm that is 0.0015% multiply your room volume by 0.0015). For example, if your room is 5 feet by 5 feet by 8 feet, your volume is 175 cubic feet (5x5x8=175) and 175 x 0.002 is 0.35. You need to release 0.35 cubic feet of CO2 into the room. Step two, in order to figure out how long the valve should be open the number of cubic feet of gas required (0.35) is divided by the flow rate.

If the flow rate is 10 cubic feet per hour divide 0.35 by 10 = 0.035 hours or (0.035x60min/hour) 2.1 minutes an hour (two minutes) That is not a lot of CO2 for a potential doubling of yields. Many timers don’t regulate below 5 minutes (see: Timers ) but you could start off having the valve open for 5 min. every hour and then increase or decrease the amount of CO2 until you see no more increases or reduced growth. As you know by now, giving your plants too much CO2 will not increase growth. You should keep the room sealed as best as possible when the plants are being given CO2. Carbon Dioxide is not toxic to plants, so if you can’t be exact, err on the side of too much. In humans, symptoms of high or prolonged exposure to carbon dioxide include headache, increased heart rate, dizziness, fatigue, rapid breathing, visual and hearing dysfunctions. Exposure to higher levels may cause unconsciousness or death within minutes of exposure. Sound scary? High levels for humans are above 2%, while what I am describing for your plants, a large increase in yields with CO2 at 0.2%, is not even close. Carbon dioxide poses no real danger to you. SmartBee Controllers are a great way to control CO2 in the grow room. Just set it and forget it!

So, buy that CO2 tank and regulator or CO2 Generator and send me an E-mail at: askthedoctor@htgsupply.com I enjoy hearing about your experiences.

Good Growing,
Dr. E.R.Myers