Marijuana Cultivation in Drought Conditions

Keeping your outdoor pot plants alive through hot summers with little rain can be nearly impossible if you don’t know what you’re doing. Guerrilla-growing expert Vinnie Kaz reveals some tips and tricks for beating the heat.

Drought Conditions = Extreme Heat and Little Rainfall

Over the last several years, outdoor marijuana crops have been relentlessly attacked by hot, dry weather conditions. In late 2012, as we were driving cross-country in an 18-wheeler, almost every cornfield we observed was brown and completely dried out. The drought of 2012 turned out to be one for the record books. In 2013 in Chicago, we had normal rainfall until early August, then nothing for the next six weeks (the hottest part of the growing season). This forced us to carry in water by hand to the gardens, which is not an easy task!

Throughout history, drought conditions have occurred in 10-year cycles, mean- ing that more hot, dry weather should be anticipated in the foreseeable future. Because the outdoor grower cannot predict the weather conditions for an upcoming season, it’s very hard to realistically plan the number of plants that can be successfully cultivated in a given year. The outdoor grower who sets out more plants than can possibly be cared for during a drought will quickly find himself (or herself) overwhelmed by the amount of work required to supply water to the crop. Hauling water to a clandestine garden beats down vegetation, leaving a trail that leads directly to your grow. The smart grower prepares for a dry growing season by formulating a highly absorbent medium—one capable of storing large amounts of rain and/or irrigation water.

Soil Mixes

Your soil mix is the most important aspect of your outdoor grow. The easiest way to ensure a bumper crop—even during a hot, extremely dry growing season — is to blend your soil mix properly, using a multitude of nutritious, highly absorbent amendments. A good soil mix will absorb and store rainfall and irrigation water, releasing it to your plants as needed. Some of my favorite amendments include:

Peat moss. Peat moss holds 20 times its weight in water; however, peat is also very acidic, so the soil mix needs to be adjusted accordingly. To increase pH, I use oyster shell flour, which is made of powdered oyster shells. It contains large amounts of calcium — and cannabis absolutely loves calcium! Using oyster shell flour instead of dolomite will vastly increase your yield. Mixing peat moss 50/50 with topsoil results in a highly absorbent soil base that is easily penetrated by plants’ roots.

Coconut coir

Coconut coir holds nine times its weight in water and is much less acidic than peat, but a great deal more expensive. Using peat moss, coco coir, topsoil and oyster shell flour is an excellent combination for growing outdoor cannabis.


Compost is a natural, slow-release fertilizer capable of absorbing large amounts of water. Be sure to test the pH of any compost before add- ing it to your soil mix: Most composts are acidic, but mushroom compost (sold now at many gar- den centers) is slightly alkaline. One of the simplest — but also highly effective — outdoor soil mixes consists of topsoil, peat moss, compost and a shovelful of oyster shell flour. Very absorbent!


Sawdust is also highly absorbent, as well as an excellent soil conditioner. It must be aged outdoors for at least two years before adding it to the soil (if it’s not aged before use, it will lock up the available nitrogen while breaking down). Sawdust is rich in potassium and calcium, and earthworms and beneficial soil microbes love it as well.


Vermiculite offers no nutrition, but it absorbs and holds large volumes of water. Look for the largest particles available, usually referred to as “coarse-grade” vermiculite.

Leaf mold

Leaf mold will hold five times more moisture than topsoil. Dried leaves are harvested and shredded during the fall. Two cubic feet of shredded leaves are mixed with one handful of lime and one cup of blood meal (for the nitrogen). The mixture is moistened and then composted outdoors over the winter. This will produce a very rich, black soil amendment chock-full of calcium, magnesium and microorganisms.

Water-absorbing polymers

Water-absorbing polymers have helped many an outdoor grower convert an unproductive grow site into a high-yielding Garden of Eden. Use up to one pound of large polymers for every 16-cubic-foot grow hole (one pound will absorb and hold some 40 gallons of rainwater). Before adding polymers to your soil, supercharge them by soaking in a water and organic fertilizer mixture. For example, I mix five gallons of rainwater with some Earth Juice Bloom and Earth Juice Grow, along with some Maxicrop powdered kelp. The polymers store and then slowly release the nutrients as they expand and contract with the rainfall. Growers using this method report triple the yields of a normally irrigated garden. When a cannabis plant has all the water she wants, a bumper crop is the result!


Once the outdoor garden soil is mixed, amended and ready to plant, plan on covering its surface with a layer of mulching material. A thick layer of mulch greatly reduces the soil moisture lost to evaporation. Proper mulching shields the soil surface from the elements, including direct sunlight. As a result, the topsoil below the mulch stays moist at all times, reducing irrigation requirements during hot, dry weather.

Mulch also adds nutrients to your soil as it breaks down. With each watering, a large amount of organic material is washed into the garden soil from above. Thick mulch absorbs moisture like a sponge, storing it for later use by your plants. The rough surface of the mulch layer contains riffles and low areas, which help to reduce the irrigation water’s run-off. The more water that soaks deeply into your soil, the less water you’ll be required to carry in by hand.

Another benefit: After a couple years of mulching, your garden soil will be overrun with earthworms. The successful cannabis gardener does everything he or she can to attract earthworms into the garden. Earthworms feed on the organic material in the mulch, converting it into worm castings, which are then excreted into the soil. Worms also crumble and till the earth, resulting in a highly nutritious, aerated soil. The worm tunnels will direct the water deep down into your growing medium.

Here’s a list of excellent mulching materials:

Hay. This is basically any chopped, dried plant material. Place a layer eight inches thick over the surface of your guerrilla garden. After a few rainfalls, the hay becomes compacted down to just a couple of inches in thickness and looks very natural. Hay also contains seeds that will grow, providing additional camouflage. Use a rake to scrape up dead leaves, dried grass, and twigs. Put the hay in a burlap bag for transportation; plastic bags will tear.

Wheat straw

In the fall, spread compost on the soil surface and cover it with wheat straw, to a 12-inch thickness. By spring, the pile will be decomposed and have compacted down to a thickness of just six inches. Female cuttings can be transplanted directly into this nutritious mulch layer.

Pine straw

This is found beneath growing pine trees, and it’s nothing but fallen needles. If there are pine trees in your area, there should be a very thick layer beneath each one. Pine straw is thought to be very acidic, but this is not exactly true: While freshly shed pine needles are acidic (4.5 to 5.0), the pine straw’s pH rises to 6.0 to 6.9 within three weeks of being dropped from the tree. Pine straw contains slow-releasing nitrogen, phosphorous, calcium, and magnesium.

Finished compost

You can also cover your soil with a three- to six-inch layer of finished compost. The compost limits evaporation and absorbs “free” rainwater like a sponge, preventing it from running off and being wasted. A decent compost will also attract earthworms to your garden.


This is not recommended — but if, for some reason, it’s the only option you have, use plastic from three to five milliliters in thickness. Also, avoid bright-colored plastics; use a camouflage-pattern plastic tarp if possible.
Plastic will prevent evaporation, but it doesn’t allow the soil to breathe or absorb rain. One solution is to punch some holes in the plastic, allowing air and water to soak through.


Newspaper is cheap, abundant and easy to carry in; if you go this route, use it to a thickness of 10 sheets. Lay the newspaper on the ground and then cover it with mulch or compost. However, plants cannot grow through the newspaper, so a small slit or hole must be made in the paper when transplanting seedlings or cuttings.

Cocoa bean hulls

Lay down cocoa bean hulls to a one-inch thickness. They have a pH of 5.8, with an N-P-K (nitrogen-phosphorous-potassium) ratio of 2.5-1.3. This makes them an excellent organic mulch material, with the added bonus of providing a slug deterrent: Sprinkle the coca bean hulls around your seedlings to prevent slugs from destroying them.

Rice hulls

Rice hulls resemble tiny straws or tubes and should be used to a four- to six-inch thickness. However, they’re a lightweight material that needs to be mixed into the soil to keep them from blowing away. As the rice hulls work their way down into the soil, they act like thousands of tiny water pipes, helping rain and irrigation water to penetrate deep into your soil.

Wetting Agents

If you’re hauling water in by hand, always add a wetting agent, which will break down the surface tension of the water, preventing it from beading up on the surface of the soil. When water beads up, a lot of it rolls off the soil’s surface and is lost to the surrounding ground.

A wetting agent allows water to absorb into the soil faster, preventing waste and evaporation loss. Faster absorption also means less time spent at the garden site when doing maintenance chores.
If the grower is pumping large volumes of water to the garden from a water tank, creek or holding pond, the soil in the garden can be preconditioned using a wetting agent. Hand-water first with five gallons of water, adding in the wetting agent at two to three times the normal amount. When the irrigation water is applied, it mixes with the wetting agent, causing it to soak in faster as well as deeper.

There are a variety of wetting-agent compounds marketed for horticultural use, and they all share the common denominator of being quite expensive, as well as having to be purchased in bulk quantities. A much cheaper method is to add two to three drops of plain, unscented dish soap per gallon of irrigation water. If you’re worried about synthetic chemicals being applied to your plants, an organic wetting agent can be made at home: simply mix 10 grams of pure soap flakes with one liter of bottled water. The soap flakes are made from a 100 percent vegetable oil base (type “pure soap flakes” on your search engine). Water treated with either of these agents is literally sucked into the soil as if by a sponge!

Collecting and Storing Rainwater

Growers without shallow groundwater available can build an in-ground reservoir or else move in tanks to store water. The tanks are filled by collecting rainwater or by pumping water from a creek or pond. The trick to storing large amounts of rainwater is to start collecting it many months ahead of the end of your rainy season.

In other words, become a water collectionist. The simplest way to collect rainwater is with a large plastic tarp. Use a tarp with pre-installed metal grommets around the edges. Just before rainfall begins, tie your tarp up in a horizontal position about three feet off the ground, using rope attached to the grommets. Tie the rope to surrounding tree branches or to fence posts driven into the ground. (Use at least six ties to protect the tarp from high winds during storms.) The only drawback to this approach is that you’ll be in the woods while it’s raining, so dress appropriately for the weather.
To direct the collected water, lay a piece of PVC pipe down the center of the suspended tarp, with one end extending out over the edge. The pipe forms a “lip” in the tarp that directs collected water over the edge and into a collection container below (use a five-gallon bucket or Rubbermaid container).

Dump the water into your holding tank, and place the bucket back under the tarp to collect additional water. To prevent the tarp from blowing around in windstorms, use as heavy a piece of pipe as possible.

Some growers punch a hole in the center of the tarp and place a rock in the center, forming a low area. Water drains into a container situated beneath the hole. Reinforce the hole with duct tape so that the tarp doesn’t tear in the wind.

A 10′ x 10′ tarp is capable of collecting 50 to 60 gallons of water per inch of rainfall — and, needless to say, the larger the tarp, the more water can be collected. (But remember, too, that the larger the tarp, the more problems you’ll have if high winds start to blow.) Set up a system like this during the rainy season, and you may be able to stash enough water for your entire growing season.

Storage Containers and Reservoirs

My favorite storage container — and probably the easiest one to obtain these days — is the plastic 55-gallon drum. In my area, they sell on Craigslist for $20. These drums are heavy-duty and have threaded, screwtop plastic lids. Find drums that were used for food storage: Mine come from a salsa manufacturer in Chicago, so they were used to ship banana peppers and jalapenos and actually smell like salsa!

Because water is heavy, place the drum in your desired location before filling it. Stash it in the middle of a thick stand of vegetation, or bury it halfway in the ground and camouflage it well. Once you have one of these drums in place, it can be used for years. UV radiation does not seem to harm these things.

One inch of rainfall and a 10′ x 10′ tarp will top off one 55-gallon drum. Use multiple tarps to fill multiple barrels at the same time. After filling, strain out any junk in the water, add a thimbleful of bleach (no more) to purify it, and then check and adjust the pH. Tighten the screw-top lid and stash until needed. If the water is being stored long-term, check and readjust pH again before using it.

Some outdoor growers bury 45- to 100-gallon Rubbermaid containers in the ground; others use plastic garbage cans. The container must have a tight-fitting cover to keep garbage and animals out.
If containers cannot be moved to the garden site, the hard-working guerrilla grower can create an in-ground reservoir. First, dig a hole, and then line it with one of the thick, rubber backyard-pond liners that are sold in home-improvement stores. Line the sides with plywood first (to protect the rubber liner from thirsty animals); a heavy piece of plywood is used as the reservoir cover. The grower can then dip a bucket into the reservoir or use a pump to move the water out.

If possible, locate the reservoir higher than your garden. This allows you to use gravity to siphon the water downhill. Each foot above the garden generates 1 psi (pounds per square inch) of water pressure in your lines. A reservoir 20 feet above your garden develops water pressure of approximately 20 psi at garden level, emitting a slow trickle at the end of the line.

Each year, Mother Nature provides the outdoor grower with a six-month window in which the proper conditions exist to cultivate — and harvest — a successful cannabis crop. Many growers do not have the facilities to run an indoor grow, while others refuse to take the risk. This makes an outdoor garden their only option for laying in a supply of high-quality weed for the winter.

In those years in which Mother Nature “double-crosses” the outdoor grower — by dialing up the outdoor thermostat to extreme temperatures while delivering minuscule amounts of  — —the unprepared guerrilla grower will likely end up with an empty cupboard or, even worse, a financial disaster. Smart guerrilla growers learn to think like Boy Scouts: Always be prepared for the worst!

The grower who plans ahead — and puts in the labor required to set up an outdoor grow as if a drought were expected — will always end up with something, even while the outdoor crops
of lazier growers shrivel up under the hot sun. Even better, when the outdoor grower sets up for a hot, dry growing season and ends up with just the opposite — i.e., heavy rainfall totals, abundant sunshine and moderate temperatures — he or she will end up with monster plants that produce a bumper crop and mind-blowing bud production, yielding more cannabis than they’ll ever know what to do with.

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