Ask Ed: Questions & Answers with the Trailblazer of Trahydrocannabinol


I live in Iowa and work on an organic farm. The government doesn’t spray?the ditches. The weed that grows naturally in these uncultivated areas looks pretty kick-ass but it’s packed with seeds. I just started growing indoors from seed and I was thinking about putting the males out on the farm with the ditch weed. Will it create better ditch weed?
Scottie 420, Internet

Yes, with some caveats. The amount of pollen your male plants will produce is miniscule compared with the pollen produced by other males in the area. Even if the male is in close proximity to a few females, the chances are that most of the flowers will be fertilized by pollen from the indigenous plants (the male ditch weed). The high-potency male plants’ pollen will be diluted by the pollen of surrounding low-potency males. Eliminating the native males would increase the percentage of buds successfully pollinated by the potent males. However, the introduced pollen might not be released at the proper time to pollinate the indigenous females, and then the numbers problem comes into play – none of the introduced genetics will carry forward unless you can replace most of the low-potency males in the population with the high-potency genes. Second-generation native males should also be removed in favor of high potency varieties. Presuming that high-potency males generated all the pollen used in fertilization for two generations, the population would have about 75% of the potency of the introduced variety.

(Editor’s note: Ditchweed is a mid-western US phenomenon. The DEA boasts of eradicating 88 million of these plants in one recent year, while also destroying 4 million high-potency cannabis plants. These feral cannabis plants are sativas which were once husbanded by humans for their fibre in the making of cloth, canvas, rope. These feral plants appear in Kansas, Iowa, Missouri, and areas off the Mississippi River by the millions each year and are extremely low in THC. This is a left-over result of industrial hemp plants that once were found from Kentucky across the Midwest USA to as far west as central Washington state from the 1700’s (in Kentucky) to as recently as 1935 in Sumas, Washington. Over decades, this hemp variety of cannabis became indigenous and feral, producing prodigious amounts of seeds each year which drop into the waste or roadside areas and pop up the following spring. ‘Feral’ is a term for once-cultivated plants that become wild. These plants are not ruderalis, a European roadside cannabis, although that is a common misconception.-Marc Emery)


What can one do about these little butterfly larvae that are eating my buds from the inside out? I think they are cabbage butterfly larvae (the green ones), and there are some grey, and some slightly bristly ones. They are wreaking havoc.
Cunno, Internet

We just discovered tiny caterpillars in the hairs of buds that are within 2 to 3 weeks of being harvested (it’s an outdoor grow). The buds turn from green to a brownish color and look like a mold or a nest, and the bugs bore into the bud. What would you do? Can you help with these needle-like creatures? Is it too late, considering we harvest soon?
Richard M., San Francisco, CA

I found some bright orange grubs or worms in the stems of my plants. They do not seem to be doing any harm to the plant; they are very small and seem to be so embedded in the stems that they are hard to remove. Are they dangerous to the plants or humans?
Arwe A. Live,

There are several ways to deal with caterpillars eating your plants. If there are only a few you can physically remove them from the garden. The problem with this technique is that it becomes tedious in a garden of any size, and any missed caterpillars will continue to cause damage. Some gardeners spread a tarp out under the plant and shake it; members of some caterpillar species will fall to the tarp, but this is also hit-or-miss and tedious. I prefer using “biological warfare” to eliminate caterpillars. Bacillus thurengiensis is a species of bacteria that causes plague in the pests. Two popular brands are Dipel® and Thuricide®. This is sprayed on the plants and when the caterpillars ingest it, they stop feeding almost immediately and die within a few days, then release spores that other caterpillars also ingest. Leaf-eating pests are easier to get to, but if you suspect caterpillars are boring into the stem, use a tube to drip the
bacteria inside.

Pyrethrum is a natural pesticide concentrated from plants in the chrysanthemum family, and is lethal for chewing insects and many cold-blooded animals. Pyrethrum sprayed on the plants will kill the caterpillars but will also kill any of their natural enemies. It is not effective on eggs either, so you may have to use it several times to catch new hatchlings – however, it loses its effectiveness after a few days of repeated use. There are many brands of pyrethrum on the market that come in convenient ready-to-use form. Pyrethrum has no effect on humans and does not negatively affect the buds if sprayed on them. If there are a few small outbreaks of caterpillars that are contained in a small area, the spots can be sprayed. A combination of neem oil added to soap insecticide is also very effective at eliminating the pests.


I grow marijuana outdoors. Can I plant some seeds at the end of July and still get some good buds from harvesting? Around here the temperature stays above50° Fahrenheit until early December.
Notorious Bowls,
Memphis, Tennessee

If the plants are just germinating in August and have only four months to grow, flower and ripen, it is unlikely that they will grow very big. To maximize yield I would use a plant that ripens mid-season, or about 70 days after forcing; some indica hybrids continue growing after they are forced to flower. Early season plants that flower in 50-65 days are likely to start flowering shortly after germination and won’t grow very large so they will have small yields. Long season varieties that take more than 80 days may not ripen until mid orlate December.


I have two five-foot plants that I started in a two-gallon pot. I recently transplanted them into the ground. I left the plants in the original pot but I took the bottom off so the roots could grow through. Now after a few days I have noticed that a lot of the lower leaves are turning yellow. Are my plants at risk of death, and if so, what can I do to save them??
J. Mezo,

The bottom leaves are turning yellow due to a nitrogen (N) deficiency. When you transplanted the plants from inside to outside, their growth rate increased because of the sunlight, which provides more energy than the indoor lights. Nitrogen is used to build new tissue, and moves to new growth from lower tissue. When the N moves out from the lower leaves, they turn yellow. To eliminate N deficiency, the plants should be fertilized using liquid fertilizers high in N. All fertilizer packages list the percentages of the three major nutrients, Nitrogen (N)-Phosphorous (P)-Potassium (K), or N-P-K, in that order. To supply extra N, use a liquid fertilizer that is higher in N than in P or K. Both organic and non-organic fertilizers are available in formulas such as 10-3-3, 5-1-1, 5-2-2 and 21-6-6. These fertilizers will supply the needed nutrients and green up your plants. Organic formulas and some others supply micronutrients as well.


I have a friend who says supplemental CO2 is a waste. He has two flowering rooms that alternate light and dark with each other, and says that because plants release CO2 at night, he can capture it from plants in the dark period and feed it to plants that are under lights. He vents the air from the dark room into the lighted space, then the air circulation reverses direction as one room goes dark and the other lights up.

Do the plants release enough CO2 during darkness to effectively feed the others without using any supplemental CO2? Is the CO2 that is released enough for the plants to benefit, or should supplemental CO2 be added?

Plants metabolize in much the same way as animals: during both day and night. The cells use sugar as fuel to support their life processes. In these processes, sugar is combined with oxygen to generate the energy that the cell uses. It releases water vapor and CO2.

When light falls on the green part of the plant, the chloroplasts, which contain chlorophyll, use the energy to combine carbon dioxide (CO2) with water to produce sugar and release oxygen. They release more oxygen than they use, so there is a net increase in oxygen and a decrease in carbon dioxide when plants are photosynthesizing.

Even so, your friend’s system will not supply the high content of CO2 that plants are able to use when they under bright light. Plants under bright lights can use between 1500 and 2000 ppm (parts per million) CO2. Meeting this amount will increase growth and yield considerably.

So your friend was right, but not right enough. His system might supply a little CO2 to the room, but a CO2 set-up (consisting of a CO2 tank with solenoid on/off valve, a CO2 sensor, and a control box) would have a profound effect on growth.


Is there a good height to let plants reach before forcing flowering? I don’t want to spend more time growing in vegetative stage than is really necessary. I’m growing from seed.

You can force flower thoroughly rooted cannabis cuttings at 6 to 8 inches though usually plants are forced to flower around 30 cm, or at around 12″ or one foot. Some varieties will only grow to 45 or 60 cm (1 1/2 to 2 ft.). Others will be 100-125 cm (3-5 ft.) tall when they ripen.

There isn’t one definite prescription for spacing, pruning or forcing because of two factors: differences in varieties’ growth habits and numerous growing styles.

Strains vary in growth habits and different shapes. For instance some strains such as Aurora Indica (Nirvana Seeds), Blue Pearl (Homegrown Fantaseeds) and California Grapefruit (DNA Genetics) have little or no branching while others, such as Blueberry Haze (DNA Genetics), Cherry Pez Livity (Apothecary Seeds), and Passion Queen ( have a candelabra or other branching formation. Growing style has a lot to do with it too. Plants are placed as close as 40 per sq. meter (4 per sq. ft.) or as few as 10 per sq. m (1 per sq. ft.). Plants grown with more distance between them will naturally spread out more than closely spaced plants.

“Sea of Green” (SOG) is the technique of growing many plants, rather than just a few, in a certain space. That way the canopy (top layer of the plants’ buds and leaves) is filled quickly. Looking down at the garden, the floor is not visible, just the canopy, Each plant has to grow just a little bit. In a garden with just a few plants it takes more time for the canopy to be filled. Thus SOG techniques save time spent in the vegetative cycle.

Plants vary in height they grow after forcing, too. Generally speaking, the more a variety is influenced by sativa heritage, the more it will grow after forcing. Varieties such as Aurora Indica, Endless Sky (Greenthumb Seeds), and Papaya (Nirvana), will grow only 50-100% taller after forcing. Other varieties including Euforia (Dutch Passion), Marley’s Collie (Sensi Seed Band), and Mazar (Dutch Passion) will grow twice as tall or more. Mantioba Poison (Great White North), forced to flower at 12 inches will ripen at 4-5 feet. (Strain and company names are from my “Big Book of Buds 2” ).

It is very helpful for the gardener to know the growing habits of the plants being cultivated. Read the information that came with your seeds if you bought them from a supplier. However, without having prior knowledge, the gardener will have to design the garden with some flexibility to accommodate different
growth patterns.


I am growing in a 2 ft. x 2 ft. x 6 ft. closet using three 40-watt compact fluorescents and my girls are doing nicely. I am enriching the air with carbon dioxide (CO2) and nitrogen (N2) from tanks. Does the N2 help? Would it help to inject both gasses into the dirt with air stones as well as into the air?
Waiting to Get High,

By volume, 78% of air is N2 found in its elemental form. However, plants cannot absorb the gas. Even injecting it into the root zone won’t help. The roots draw the element from the water only as a nitrate or nitrite. You can turn off the N2 since it doesn’t help.

Plants use CO2 as one of the ingredients in photosynthesis. This is the process in which plants use energy from red and blue light to combine carbon dioxide and water to create simple sugar and release free oxygen into the air. Since the process occurs only during the light period, most plants (including cannabis) absorb the CO2 through their stomata – a plants’ equivalent of pores – only when there is light. The only parts of the plants that use CO2 are the green parts. Their cells contain chloroplasts where the sugar is manufactured.

In addition to photosynthesis all plant cells maintain life process or metabolism. In much the same way as animals, the cells combine the sugars they manufacture with oxygen to power their metabolism. Upper parts of the plant absorb their oxygen from the air, of which oxygen makes up 20%. Roots absorb oxygen (O) from the air in the water and soil, and in some growing systems it is injected into the root zone. As root cells metabolize they emit CO2. This is removed from the soil or water and absorbed by air on contact. In return, the medium absorbs fresh oxygen from the air. Adding CO2 to the root zone would hurt, rather than help, the roots.


I’m building an ebb-and-flow hydroponics system supplemented with an ultrasonic fogger. I’m thinking of enriching the root system with oxygen by injecting 95% oxygen gas via air stones into the root zone. Do you think this will help significantly with plant growth?

Adding oxygen (O) to the root zone will increase root health and resistance to disease. It will allow the roots to function at near optimal levels since they will have easier access to oxygen, which they need to maintain their life processes. (Editor’s note: some definitions for the unfamiliar: ‘ebb & flow’ is a method of growing that uses a nutrient solution that is released in timed intervals to wash over the roots. Unused nutrient flows back into a reservoir and is pumped into the root areas when required. An ‘ultrasonic fogger’ is a quiet (ultrasonic) pump that mists the roots in oxygenated nutrient solution.


I was reading about metal halide (MH) bulb usage when I saw a warning about UV emissions. The author stated that if the protective glass around a metal halide were to break, you should unplug it immediately because without this glass, the metal halide would emit harmful levels of UV radiation. I read one of your books that mentioned increased UVB increasing the THC production. [The discussion in “The Best of Ask Ed” was about research that showed THC content of high-quality plants increased in direct ratio to the amount of UVB light they received. –Ed.] I have been looking for a good source of UVB supplementation. Have you ever heard of anyone removing the glass from a MH to increase UVB, and how much increased UVB would be received? Or is it unsafe to do this?
J. Barn,

It is VERY unsafe to use a MH with a broken outer bulb. Not only does it emit harmful UVB rays that cause sunburns in great quantity, it also releases UVC light, which is deadly to most life forms. This is not something you want to tinker with. MH lights emit more UVB light than high-pressure sodium (HPS) lights, so switching to MH lights will increase the amount of UVB light the plants receive. Other easily accessible sources of UVB light are reptile lights, which emit about 10% UVB, and tanning lamps, which emit both UVA and UVB light – but if you use these, turn them off while you are in the room.


I have a small garden about a meter square (39 in. x 39 in.) and I’ve used CO2 before in the form of club soda without salt added (seltzer). I’m not satisfied with the results; I did get a good harvest but I don’t think it was worth the effort. I don’t want to invest hundreds of dollars into a CO2 tank for such a small garden. What do you think about Alka Seltzer? When mixed with water it emits large quantities of CO2, quite a bit more than club soda – plus it’s cheaper, easier, and it seems like it would be more effective.
Nick V.,
Cameron Park

I get a stomachache just thinking about how much Alka-Seltzer will cost you and how ineffective those little pills will be! They will supply the plants with occasional bursts of CO2 but won’t supply them with constant enrichment during the light hours. CO2 units that measure gas in parts-per-million and add supplements, as needed, can be a costly up-front investment, but is well worth it! You will increase the yield considerably, and it will cost pennies a day to run in a small garden.

As for seltzer: gardeners find that spraying seltzer on their seedlings increases their growth and stem stoutness, but it isn’t a good idea to spray buds with water, especially as they near ripening.


I have three different strains growing in a flood-and-drain hydro unit, and they have different harvest times. How do I flush with just water for the last two weeks of the first and second strain to be harvested?
Green Bud, NC

I don’t know of a way to flush only some of the plants and not others. Does anyone have any suggestions?


I want to set up a garden but I am afraid of using the electricity because of power company narcs. I’m thinking about buying a 2000-watt super-quiet camping generator to supply all my electric needs. It would run a 1000-watt light and all other necessary equipment. What do you think?

I think it’s a good idea, but with several caveats: buy a generator that is built to run for extended periods of time rather than for just a few hours at a time; ensure that the generator is really quiet so it doesn’t disturb you or your neighbors; keep the generator located in a convenient place to fuel and service; and make sure that the emissions are properly vented. If you have a choice of natural gas or gasoline, choose the natural gas because the emissions have fewer impurities (just water and CO2) and can be vented into the garden to increase CO2 levels.


I have sprouted some seeds I brought back from Amsterdam, and my nephew says that males have branches directly opposite each other and female plants always have alternating branches. Is that always the case? All four of mine have branches exactly opposite, so I’m hoping he’s wrong.
Melissa D.,
San Francisco, CA

Your nephew is wrong. Cannabis seedlings have leaves that grow on opposite sides of the stem (decussate phyllotaxis), and only when the cannabis plants are getting ready to flower do the branches begin to alternate (distichois phyllotaxis). This phyllotaxis, or genetic branch pattern, occurs for both males and females. As the plant ripens, it released hormones that signal this change. If you want to determine sex of your plants at an early time, you can look for indicative pre-flowers appearing at branch nodes in the fourth to sixth week. By the eighth week, when the plants are in a vegetative state, you may be able to determine the sex by looking at the pre-flowering signals with a magnifying glass. You can also snip a shoot off your plant and put it in water under 12 hours of light; it will show sex within 15 days. When using this method, carefully keep track of your different plants and cuttings – use labels to match up cuttings to the appropriate parent plants.


I have a garden blooming in an inconspicuous 3 ft. x 3 ft. (1 m2) corner. A fan is used to keep the heat of a 400-watt HPS under control. When clueless visitors drop by I temporarily turn off the fan and the HPS light, and turn on a compact fluorescent light to prevent interruption of the light cycle. When guests leave an hour or so later, the fluorescent light goes off and the HPS and fan go back on for the duration of the daily light cycle. This prevents guests from hearing noises they
shouldn’t hear.

Does a sudden shift to a compact fluorescent light prevent the garden from “thinking” it is in the dark cycle? Can a brief change in light spectrums affect
the garden?
Shy Greenling,

Plants don’t measure interruptions during the lighted period; they measure the length of the uninterrupted dark cycle. Turning off the light during the light cycle won’t affect the plant except to temporarily stop photosynthesis. So you don’t need to turn the fluorescent on when strangers are around. The rate of photosynthesis depends on the intensity of the light. Turning the fluorescents on will stimulate a slow rate of photosynthesis, rather than none at all. The change from HPS to fluorescent and then back to HPS will not hurt the plants. Just make sure that the dark cycle is not interrupted with light even for a few moments, because that restarts the chemical countdown for forcing flowering. In order to induce profuse flowering, most marijuana varieties require between 10-12 hours of uninterrupted darkness that begins and ends at the same time every day for two weeks.


I have always been led to believe that the black root aphids discussed in CC #55 are one of the life stages for fungus gnats. They are a real problem for me, and due to the restrictions on pesticides here in BC, very hard to combat. I tried pyrethrum-based treatments, but they always returned.

A botanist who runs a gardening business told me he uses 35% H2O2 added to water. I soaked my soil with tap water and let it sit for an hour, making sure it was damp – not soaking wet – throughout. Then, using a standard store-bought watering can, I applied a solution of 2 cups of H2O2 per 2 gallons of water to the bare soil; the soil actually started fizzing during application.

It worked: the fungus gnats were gone, and have never returned. That simple solution really did the trick – not to mention added oxygen to the
soil. Now I water with a milder solution of 1/2 cup per 2 gallons once every two weeks. My plant roots are always healthy and white because the H2O2 releases all its oxygen into the soil as it breaks down.
Weed 1503,

While you have a good solution for eliminating the insects in unused soil, the concentrated solution cannot be used with live plants, for fear of burning the roots. However, your dilute solution is a good prevention method and does increase the oxygen available to the plant.
Fungus gnats lay eggs on the soil and the larvae (little maggots) migrate to shallow soil layers to feed on roots and decaying matter. They are tiny, but you can sometimes see them floating or wiggling in puddles after watering. They are white and can have tan or grey shading. Root aphids are larger – perhaps a sixteenth of an inch long – fast moving, light-hating insects that feed on the roots. They are usually black, but are sometimes lighter shades of brown.

An organic method of getting rid of both the fungus gnat maggots and root aphids is beneficial nematodes (Seinernema feltiae). They attack all kinds of underground insects and are harmless to humans and pets. Fungus gnats are easily controlled using bacteria that attack only gnats and other flies. It is called Bacillus thuringiensis var, israelensis (BTI) and is the active ingredient of the product Gnatrol®. Botanigard ® is composed of a fungus, Beauveria bassiana, which attacks aphids, whiteflies and thrips. It is recommended as a spray for use above ground but it can be used as a drench to destroy root aphids.