Soil is made up of mineral particles mixed together with living and dead organic matter that incorporates air and water. Three basic factors contribute to the cannabis root’s ability to grow in a soil: texture, pH, and soil temperature.

Soil Texture

Soil texture is the size and physical makeup of the mineral particles. Proper soil texture is required for adequate root penetration, water, and oxygen retention and drainage as well as many other complex chemical processes. Clay or adobe soil is made up of very small, flat mineral particles; when it gets wet, these tiny particles pack tightly together, slowing or stopping root penetration and water drainage. Roots are unable to breathe because very little or no space is left for oxygen. Water has a very difficult time penetrating these tightly packed soils, and once it does penetrate, drainage is slow.
Sandy soils have much larger particles. They allow for great aeration (supply of air or oxygen) and drainage. Watering frequently is ideal because water retention is very low. The soils water and air retaining abilities and root penetration are a function of texture.
Loam soil is also good for growing medical marijuana. It contains a mix of clay, silt, and sand. The different sized particles allow a large combination of pore spaces, so it drains well and still retains nutrients and moisture.

Soil pH Levels

Soil pH levels are measured by acid-to-alkaline balances and they range from 1-14, 1 being the most acidic, seven being neutral, and 14 most alkaline. Marijuana grows best in soil with a pH from 6.2-6.8. This level range will allow the marijuana plants to absorb and process available nutrients most efficiently.

Temperature of Soil

Raising the soil temperature speeds the chemical process and can hasten nutrient uptake. Cannabis grows best in soil with temperatures ranging between 65-70*F (18*-24*C). Warm the soil with soil-heating cables or a heating pad. fasten heating cables to a board or table and set a heat-conducting pad on top of the cables to distribute heat evenly. Set cuttings and seedlings in shallow growing trays on top of the heat-conducting pad. Never let the temperature of soil drop below 65*F.