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Resources for Growing Quality Medical Marijuana

Soil Primer

Authors: Old_Phart

Growing MJ is easy enough. You can just plant seeds and let them grow or not, on their own. But, MJ is a plant in very delicate balance with its environment, for all its apparent strength. As with people, whether or not a plant merely survives is not a real issue. Balance should be created between the vital forces in the plant and the beneficial aspects of the environment, if its life is to have “high” quality. Therefore, our GOAL is to create a soil environment conducive to the growth of healthy vigorous MJ plants.

Properties of Soil

The soil serves as a source for water, air and nutrients, and to anchor the roots. Since MJ grows fast it requires more water and nutrients than most other plants grown indoors. Success of growing MJ depends on supplying the plant with a medium that meets its needs without creating toxic conditions in the process. Mel Franc states “There is no such thing as the perfect soil for cannabis”. However, we do know that for healthy, full growth, MJ at least prefers a medium with good drainage (texture), which is high in available nutrients and is near neutral in PH (6.5).

Texture

The texture of the soil determines its water holding and draining properties. .MJ must have a soil that drains well for healthy growth. In a well-drained soil the roots are in contact with air as well as water. Soils with too much clay, or overly rich in compost or organic matter, tend to hold too much water and not enough air. Soils that are too sandy or contain mostly fine particulate matter will not hold enough water.

Dry soil should never cake or form crusts. Dry or slightly moist soil that feels light, airy or spongy when squeezed, and has a lot of fibrous material, will hold too much water. Mix it with materials such as sand or perlite to decrease its water holding capacity.

Wet soil should remain spongy or loose and never sticky. A wetted ball of soil should crumble or separate easily when handled. If the soil is heavy with fine particulate matter, or is sandy or gritty the addition of vermiculite or some sphagnum moss would be beneficial.

Nutrients

Nutrients are essential minerals necessary for plant growth. The major nutrients are nitrogen (N), phosphorous (P) and potassium (K), which corresponds to the three numbers, in that order, that appear on fertilizer packages and that give the percentage by weight of each nutrient in the mix.

During the vegetative phase of growth MJ prefers a soil that is high in nitrogen and mid-range in phosphorous and potassium or a ratio of 2 times the amount of nitrogen to each of phosphorous and potassium (2-1-1). Example: a fertilizer with an NPK of 10-5-5 (percent by weight in the fertilizer mix) would be a ratio of 2-1-1. During the flowering phase of growth MJ prefers a ratio of 1-2-2.

There are many prepared organic and chemical fertilizers available that can be mixed with soil to achieve the desired nutrient concentration. When using organic nutrients remember that organic materials take time to break down and become available to the plant at different rates.

Do not use fertilizers that come in pellets or capsules or that are labeled “timed” or “slow release”. They do not work as well indoors as do standard organic or chemical fertilizers.

PH

The PH is a measure of the acidity or alkalinity of the soil medium. It is measured on a scale of 0 to 14 with 7 assigned as neutral. Below 7 is acid and above 7 is alkaline. PH affects whether nutrients dissolve to forms available to the plant or to forms the plant can’t absorb, remaining locked in the soil. MJ responds best to a PH of 6.5.

The easiest way to check PH is with a simple soil PH test kit (available at most garden centers). They are not extremely accurate but, will give you a “ball park” indication of PH. Soil PH meters are available and are best to measure exact PH.

Commercial soils are seldom found to be too high (alkaline) in PH but, are often found to be too low (acid) in PH. High alkaline soils can be treated with sulphur compounds (e.g., iron sulphate) to lower PH. High acidic soils can be treated with lime to raise PH.

General Characteristics

Texture, available nutrients and PH of a soil are all related. However, the most important single factor is texture (good drainage). With poor drainage “bad” bacteria (anaerobic) are created that thrive without oxygen. They displace the beneficial microbes that require oxygen in order to thrive (aerobic). As they break down the organic matter, CO2 and organic acids are released into the soil. These acids lower the PH causing available nutrients to be “locked out”.

This concludes OP’s Soil Primer. I hope it helps people new to growing understand what to consider when preparing soil for growing MJ.

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