Ask Ed: Grow Questions and Answers

Do you have a grow question (or answer) for Ask Ed? Send mail to: Ask Ed, PMB 147, 530 Divisadero Street, San Francisco, CA, 94117, USA. You can also email and check out his website Submitted questions featured in CC will be rewarded by Ed Rosenthal with a copy of his book Best of Ask Ed: Your Marijuana Questions Answered. Sorry, but Ed cannot send personal replies to your questions!

I’m growing in a closet using a metal halide (MH) bulb in a reflector with a glass cover that says it is a UV shield. I’ve read that the more UV radiation a plant gets, the more THC it produces. Should I take the cover off my lamp?
Mike M,

Yes. It will make the buds more potent; in controlled experiments it was proven that the production of THC in high quality plants increases in a direct ratio to the amount of UV-B light they receive. Get ready for some super powerful buds.

Metal halide lamps emit more UV-B light than high-pressure sodium (HPS) lamps, so for more potent buds it is a good idea to use MH lamps the last 10 days of flowering. Air-cooled light reflectors have glass covers that absorb UV-B light. If it is feasible, remove it, so the light can shine unobstructed on the plants. To prevent the garden from overheating, keep the inline fans on, which will draw air in from the garden space to cool the lights.

Tanning and reptile lights can be used to increase UV-B levels. Both fluorescent and halide lights are available; reptile lights are available only in fluorescent models. Make sure you turn off high UV-B lamps before entering the garden, as UV-B rays are associated with skin cancer.

A few months ago I noticed that a toad had taken up residence in my clone room. He is still living there, and apparently thriving. It seems to have completely eliminated the formerly resident population of gnats and flies, which makes this creature pretty valuable to me. Any tips on the care and feeding of toads? What easily obtained insects will provide him with tasty sustenance without attacking my baby plants?
Kermit T. Frog,
Sesameville, Newfoundland

Toads are very useful in any garden or grow room. All garden toads consume hundreds of different insects that can infest a garden, including snails, beetles, moths, aphids, gnats and flies. I could find no experience indicating toads consume spider mites, however. Beware that the use of any toxic pesticides, insecticides, and tobacco-based anti-mite formulas in the garden area will kill toads and frogs immediately, so toads can only be used in completely natural gardens. Use a species of toad or frog that is native to your area, non-native species that escape into the environment can disturb the reptile environment considerably.

Swollen Sensi Star mature bud development.  The hairs are darkened.Swollen Sensi Star mature bud development. The hairs are darkened.If you only have one or two toads amongst twenty or more plants there may be enough insect regeneration to provide a continual diet for your toad while keeping mature insects to just a few, especially if your grow room is above 80° F (26.7° C) where insect multiplication advances rapidly. A small toad house, available from any garden center, is good to place among your plants; or you can turn over a terracotta plant pot and knock a doorway out for your toad home. A good toad house should be cool, airy and provide shade. Toads are nocturnal and will avoid the direct rays of your light bulbs to avoid dehydration. Clean, nutrient free water should be nearby in a bowl so the toad can soak in and drink it. Change the water daily.

(As an aside, I learned that cigarette smokers who casually throw away cigarette butts actually kill hundreds of thousands of toads and frogs each year, as nicotine is extremely toxic to reptiles, and rainwater
washes the nicotine into toad and frog habitats.)

I plan to regenerate a Chronic Skunk (from Willy Jack seeds) plant after harvesting ripe buds. I will leave some small buds on the plant when it enters regeneration. What will happen to these buds during regeneration? I want to stop feeding the plant 2-3 weeks before harvest and use plain water. How will this affect the growth of the under-developed, smaller buds?
Anxiously Awaiting Harvest,

In order for a branch to regenerate it must have some leaf material on it. Frequently, the leaf material and small underdeveloped buds are interspersed. In order to leave green leaf on the plant some bud must also be left. This bud will never really develop as the plant turns to vegetative growth. The plant may be somewhat nutrient starved by harvest time. As soon as the plant is trimmed it should be placed under continuous light and fed with vegetative growth formula fertilizer.

There are little white worms under some of the leaves. What are they?
Lava Electric,

They are probably caterpillars that have hatched from eggs laid on the leaves. They can be picked off by hand or washed off if you have one or two plants. If they are more of a problem use Bacillus thuringensis, a bacterium that is specific to caterpillars and can do you and your pets no harm. Some brands are Dipel and Thuricide. Pyrethrum, an insecticide made from a plant closely related to chrysanthemums, is also very effective in eliminating the pests. It should not be used near cold-blooded animals such as reptiles or fish.

Bags of dry, cold shake ready to cold water extract.Bags of dry, cold shake ready to cold water extract.LOSING POTENCY
How long does green bud remain potent after it is placed in dime baggies?

The small plastic bags are made from the same kind of material as zipper bags, polyethylene plastic. This plastic can develop a static electrical charge that is positive. It attracts negatively charged materials, including marijuana trichomes. If you’ve ever carried a baggie of pot around, you may have notice the inside of the plastic has become covered with trichomes. If you tried to scrape them off you discovered that they were bound to the plastic.

Trichomes develop a static negative electrical charge to counter balance the positive charge on the plastic. As the buds scrape against the bag the exposed trichomes break away from the bud and bond with the plastic. As they do this the potency of the smokable bud is lost. The more the buds are handled or scraped across the plastic, and the smaller the bud pieces are, the higher percentage of loss. Large buds lose surface glands but not inner ones. Keeping a baggie in your tight jeans is a bad idea because the bud scrapes against the plastic and gets broken up, exposing more surface area and losing more trichomes.

I live in Macedonia. There is a lot of cannabis growing as a weed. The variety is not like the Russian type. For one thing it is because of the climate in my country (hot and long summers with lots of sunshine). The Macedonian weed is more like sativa than ruderalis, does not flower early, is much more potent and big budded. I’m planning on cross breeding this local
variety with White Widow and Northern Lights females. How would I cross all three varieties?

Use the pollen from the Macedonian to pollinate the WW and NL. Then standardize the two separate hybrids over five or six generations. Then cross the two new strains. That will create a hybrid that is 50% Macedonian, 25% WW and 25% NL. Once these crosses are stabilized they can be used to make many new hybrids.

I’m starting a grow?area-with fluorescent lighting. I have four 48″ fluorescent 2-tube fixtures with warm and cool spectrum tubes and a 65-watt CFL (compact fluorescent light) twist bulb. If I?mount all the 48″ tubes vertically in a circle with a 30″ diameter and then mount the 65-watt CFL twist above the plants, will I need to add more lights or anything else?

The garden will work well and the plants will produce bud all along their length. I suggest that you grow no more than four plants in the space, although you could use fewer plants. If you placed reflective material between the reflectors, no light would escape the garden, increasing your growth. For convenience, you could use poster board to serve that purpose.

I’m having trouble with a Northern Lights/Haze cross that I’m growing. It is quickly outgrowing the vertical space. I am using a 12/12 cycle to flower and the garden is in the fifth week of flowering. The plants are developing great bud formation but they are getting too tall. Can I reduce the photoperiod to 10 or 11 hours to hasten ripening so that they won’t outgrow the space? Is it possible to place the entire plant on a slant to gain extra head room as well?
The Doctor,

Many sativa hybrids are not suitable for indoor planting because they get too tall and are fairly uncontrollable. In addition, many varieties need more light than they usually get indoors under lamps to bud well.
There are some solutions to the problem of plants that are growing too tall for the garden. As you mentioned, cutting the number of hours of light to 11 or 10 daily will hasten ripening. Placing the plants at an angle so they don’t reach as high is another good idea. Another method that you might try is to bend the top branches so that they are horizontal to the light. The buds on the top branch will continue to grow, but the branch won’t grow much longer and it won’t grow higher. Another method of controlling height is by reversing the temperature pattern so that it is warmer at night than during the daylight hours. The stems naturally grow shorter under this regimen. A good temperature range is 68°F (20.3°C) during the day and 78°F (25.6°C) at night.

I have buds that are kind of airy. Is there a way to get them to tighten up?
Sweet 50s,

If the buds have already grown fluffy and airy it is too late to fix them now. Usually airiness is a sign of too much heat. To grow dense buds the temperature should be kept below 80°F (26.7°C), and is best kept between 70-75°F (X21.2-23.9°C). When the temperature goes above 80°F, buds grow lanky and airy. One spike in temperature usually won’t create a detectable difference, however the lankiness will become more pronounced the hotter it is and the longer it lasts. Think of this in terms of days rather than a few hours. In the future, reduce the temperature the plants experience. Indoors, this can be done by using air-cooled or water-cooled lights, improving ventilation or adding air conditioning. Outdoors, the plants can be kept cool using water sprayers that emit 5-10 micron-sized droplets. The water evaporates in the hot air, cooling it. No moisture reaches the plants, just the cooled air. These systems use very little water to cool large areas outdoors. They make a big difference in areas that experience temperature over 80ºF during flowering.

I’ve been using bubble bags with excellent results. Is it preferable?with this process?to use?dried or fresh leaf?
Terry B.

When hash from fresh grass is fired up, it starts to bubble. That is caused by the evaporation of water that was bonded to the THC molecule. The heat induces it to separate at which point the THC becomes active. Only after the water has separated does the THC burn or vaporize. In the growing plant, THC is held as THC acid, a mole-cule with water attached. When marijuana dries the water evaporates. With fresh bubble hash, the heat causes the separation as the water boils away. This is important because THC becomes more potent when the water molecule is released, a process called decarboxylation. When dried grass is used to produce water hash, the THC has already lost its water and is active. Water hash can be dried prior to use by placing it in a warm area.

The feral hemp pictured here has adapted to the climate of north central Europe, but it doesn't get you high.  It could be used in hypridization program to create a poten adapted variety.The feral hemp pictured here has adapted to the climate of north central Europe, but it doesn’t get you high. It could be used in hypridization program to create a poten adapted variety.MARSHY GROWING
I would like to grow in a marshy area. During most of the spring and a good part of the summer the land is so wet that when you walk on it, your boot sinks an inch and a little water puddle forms. How can I keep my plants happy in this environment? The only plants on the land are some small bushes and tall grasses. It’s very remote and I don’t have to worry about security.
Dan G.,
Providence, RI

You might want to buy back-issue CC #60 for the “Swamp Growing” article, which offers three different ways to grow in swampy and marshy conditions. For now, here are some suggestions.

The soil in the marsh is probably very acidic, mucky, and dense so it holds too much water and not enough oxygen. In order to be used it has to be modified using materials to create a lighter soil with larger particles so that it holds both water and air. Wood chips, pebbles, dried leaves, charcoal pieces, sand, and perlite can all be used to provide texture if the soil is fine and doesn’t provide enough air space. It should be tested for acidity and lime should be added to raise its pH to 6.1-6.5.

In order to keep the soil from staying soaked it should be mounded into hills at least a foot above the soil line. This keeps it above the saturated soil and allows the soil to dry out. Other methods of dealing with the problem are to import planting mix and use it to build hills or planting beds or to grow in planting bags. Then you can use the location without going through the arduous task of amending the soil.

If importing planting mix is too onerous, you could develop your own very fertile compost on the spot. In the fall or early spring make large piles of gathered leaves and other vegetation and mix them with a high nitrogen (N) fertilizer such as fish emulsion, cotton or alfalfa seed meal, or even a soluble nitrate. An inexpensive vegetable or flower mix such as a 10-10-10 (Nitrogen-Phosphorus-Hydrogen) can also be used to assure that the compost is rich in nutrients. You could also use dried steer or chicken manure, but they are not very concentrated. If the nutrients are granular, mix them in as you build the pile. Liquids such as fish emulsion can be watered in after the pile is built. Use much more fertilizer than you would to feed the plants.

The N is used by microorganisms, which break down the cellulose. During the first stage of the process they are so active that the pile heats up and can feel uncomfortably so if you place your hand inside it. The heat helps kill weed seeds and many pathogens. As the process ends, the pile will shrink to about one-fourth or one-fifth of its original size, transforming into rich, fertile compost with a delicious earthy odor that is ready to support your crop. The roots will grow through the mix to the more saturated soil, and will adapt as long as there are also roots in the compost, where they can obtain oxygen from the looser medium.

Remember: marshes and swamps are ecologically sensitive areas, so adding too much fertilizer or chemicals will damage the ecosystem. Try to grow organically in these areas if possible.

I planted some varieties that weren’t ripe when I had to cut them due to cooling weather and cloudy skies in mid-October. If the plants had been growing indoors I would say they were two weeks away from peak harvest time. What can I do to harvest ripe buds next year?
New Hampshire

There are two solutions to your problem. Either change the variety or force the plants to flower early. The varieties you used were not adapted to the latitude they are growing in. Choose varieties grown by successful local growers or look for fast maturing, short-season varieties. Outdoor varieties bred for growing in Holland, Germany and southern Canada will mature in late September in your area. You will avoid some of the bad weather and the declining intensity of the sun’s light as autumn approaches. You could also use some of the auto-flowering varieties that mature in 100-120 days from germination. If they are started early enough they could mature in August under stronger sunlight.

Shading the plants each day for 12 hours under opaque curtains or by moving the plants to dark quarters can also be used to hasten flowering. If the plants are covered each day beginning in early summer they will mature much earlier. For instance, if they are shaded beginning June 1, they will mature 60-70 days later, on August 1-10. The sun is much more intense at this time than a month or two later, so the buds will be larger and more potent than if they are harvested in October.

Do the newer self-contained grow closets really work, and do they produce quality buds? Can they be used for tall sativas? My concern is the grow space and height available in these units. ?

Although the grow closets vary a bit in size, they usually are about 4 1/2-feet wide, 2 1/2-feet deep, and a little more than four feet tall. The actual useable height is less because of the hydro system or planting containers and the lights contained within. The growing units are usually totally automatic: lights, ventilation and irrigation are regulated by a master control. Lighting is usually provided by a 400, 600 or 1000-watt HPS lamp. CO2 gas is available as an option using a tank and regulator.

These machines create convenient spaces to grow high quality – even outstanding – buds. The walls surrounding the garden keep the light from escaping and redirect it back to the plants. This creates a brighter environment than is maintained in many small gardens using the same lighting equipment. The only potential problem is excess heat that causes lanky, airy buds. The maximum temperature during flowering should be no higher than 80°F and is best kept under 75°F, as discussed in an earlier answer this issue.

Depending on the grow box design, the plants will be able to grow two to three feet tall at maturity. The best way to grow plants this small is to use plants that are mostly indica, rather than sativas. If they are forced to flower when they are about a foot tall they will grow no higher than two feet at maturity. Since they don’t have much chance to branch out, more plants are used to fill the area. This is called the “Sea of Green” method.

Rather than settle for a short grow box, to accommodate larger plants you could adapt cabinets, wardrobes or closets, which all have more height. Then you could grow a controlled sativa hybrid. If it is forced when it is one foot tall, it will grow to three or four feet at maturity. It continues to grow through the early part of flowering and stops completely when the flowers have only a few weeks to ripen.

What are the pros and cons of metal halide (MH) and high-pressure sodium lights (HPS)?

MH lamps produce less light than HPS lamps and less is useable by plants, which use primarily red and blue light to most efficiently power photosynthesis. Therefore, growth under MH lamps is slower and yields less. On the other hand, MH lamps have a less conspicuous and suspicious spectrum than HPS lamps.

MH lamps emit more UVB light than HPS lamps. In high quality marijuana plants the percentage of THC (and probably of the terpenes) increases in direct ratio to the amount of UVB light the plant receives. The result is that buds ripening under a MH lamp have a higher THC content than those ripening under an HPS.

One way to take advantage of the qualities of both lamps is to use ballasts that can accept either lamp or to use conversion bulbs. During the vegetative and most of the flowering stage use HPS lamps to promote growth and yield. Then switch to MH lamps for the last two weeks of flowering to increase potency.

When is the best time to top your plants to get two or more head buds? I am growing indoors.
London, England

Marijuana varieties differ in their shapes and growth pattern. Some are shaped like pine trees, some like conifers, and some have more bushy or candelabra shapes. Most varieties will produce a higher yield if the top branch is topped; that way, the branches that would have been the secondary top branches grow much bigger. The best time to top the plant is about two weeks before flowering. Then the secondary branches have time to fill out and build infrastructure so they can support rapid flower growth.

Cold dry cannabis pressed over a metal screen.  Resin heads collect below.Cold dry cannabis pressed over a metal screen. Resin heads collect below.GROWING GIANTS
I am planning to grow at the south edge of a clear-cut forest area. It gets light all day and has already been replanted with wildflowers and young trees, which are about six feet tall now. My idea is to grow my own miniature forest of five-foot plants between the trees, and to grow other much taller ones against the clear-cut. I have collected seeds for both varieties from friends in the area. What should I do about the soil? How should I feed the plants?
Planter Bob,
Victoria, BC

Forest soil is rich and well draining but quite acidic and should be adjusted to a pH of about 6.1-6.5. At that range all the nutrients are available and the plant will thrive. At a lower pH the plant will be slow growing and look sickly. Northern forest soils usually
hold large quantities of nutrients so you may not need as much fertilizer as you might expect. Before starting to adjust the soil, have it tested at a local soil service. The report will tell you the pH level and the nutrients that it holds, along with recommendations for making adjustments. The pH can be adjusted with dolomitic or hydrated lime powder, which takes a few months to act on the soil. For faster action, use potassium bicarbonate or “pH up”. Add a little at a time until the soil tests in the acceptable range, then it will be ready to use.

I have some excellent varieties growing. At the end of this crop I plan on being away for about six weeks. Do you have any suggestions about how I can keep the strains going during this time?
Travel Gal, Internet

There are several things that you can do to keep the varieties. If you were going for a shorter period, say three weeks or so, I would suggest placing cuttings in a moistened plastic bag and putting the bag in the vegetable chiller section of the refrigerator. The cuttings would still be ready to clone when you returned.

For the longer trip you will have to take more elaborate steps. You could keep clones in a cold place such as a refrigerator, but with a dim light illuminating them continuously. They would probably survive at about 40°F (4.4°C) for more than six weeks. They must be kept moist so they don’t dry out.

Another idea is to use an automatic watering system to keep the plants irrigated, and give the plants a diluted fertilizer solution to slow their growth. Then give them only 10-12 hours of light a day, but not in one long period – instead, the light should go on intermittently,
for 2-1/2 to 3 hours out of every 6. That way the plants don’t get long periods of darkness that could push them into flowering, but they
get a limited amount of light so they don’t photosynthesize much.

The intensity of the light and the temperature should also be lowered. Either use fewer lamps or raise them so that less light gets to the garden. Plants grow much slower with temperatures in the high 50 to lower 60ºF range than at high temperature. By lowering the temperature, the growth rate slows to a crawl. When the plants are returned to high growth conditions they respond quickly and exhibit no permanent damage.

Less promising but always a possibility: let a trusted friend watch the garden for you.



  1. Anonymous on

    I have some plants that are under lights and are about 2 feet tall. They are allready in the budding stage. What will happen if I transplant them outside right now? June 25

  2. Anonymous on

    i have noticed that led lighting is less in wattage and was wondering since rules of thumb are that .5 grams of flower grows per watt . so if this is done pryor with hps say 4oo watt . how would a 90 watt led make up the difference to make better yields? or do you still need the same watt to .5 gram ratio when growing with led lighting?

  3. dangerous on

    im no expert but not all strains go like a bat out of hell all the way through 12/12 some save it for the end if the plant looks healthy i wouldnt worry it will come if ur tips are burned then back off the feed. hope this helps

  4. Anonymous on

    kill it carefully and mist ur plants to kill any viable pollen


    i have already germinated my three white widow seeds..they have sucessfully sprouted..i have fox farm california brand i start off with just placing them in the pot a few inches down ..sprout down and start with 100watt lighting than go up to my 400watt after 3weeks???

  6. Ray on

    I’m using LED lighs for the first time. I’m flowering indicas that should be finished in 8 weeks. However, They are now 5 weeks into flowering and have not gotten any bigger than when they were 3 weeks into flowering. I welcome any advise.

  7. richi on

    the cluster of fingers you see are probally just a trait from the strain I had one strain had only gave one finger leafs didnt look like a cannabis leaf at all. Male pollen sacks look just like sacks or tiny balls. they ar clustered but do not look like leaves at all. Just leave it alone and enjoythe fruits when they are ready.

  8. jeremiah on

    Send your grow questions (or answers) to Ask Ed – Send mail to: Ask Ed, PMB 147, 530 Divisadero Street, San Francisco, CA, 94117, USA. You can also email and check out his website