Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

which is always colder than the ambient temperature. Increase soil temperature by moving pots up off the floor a few inches. Set them on an insulating board or piece of Styrofoam™.
    Soil temperatures that climb above 75°F (39° C) dehydrate roots, and at higher temperatures the roots actually cook! It is relatively easy to heat the soil in a pot. If the light or any heat source is too close to small pots, it can easily heat up the outside layer of soil where the majority of the feeder roots are located. Once destroyed, roots take one or two weeks to grow back. Two weeks accounts for one quarter of the flowering cycle!
    The more feeder root hairs there are to absorb water and nutrients, the faster and stronger plants will grow. Once roots go beyond their comfort zone, they send stress signals to foliage and stomata via hormones to close and conserve moisture.
    Oxygen is essential for clones that are growing roots. Water holds under one percent dissolved oxygen at 70°F (21°C). Bump the temperature up to 85°F (29°C) and it holds less than 0.5 percent oxygen.
    Root temperatures below 40°F (4°C) make water expand, which causes cell damage. Temperatures above 92°F (33°C) cause excessive vapor pressure within the roots, which can cause damage. At high temperatures roots send stress signals to shut the leaves down before damage can occur.

Potting Soil
    Potting soil fresh out of the bag often fulfills all requirements for a growing medium: good texture that allows good root penetration, water retention, and good drainage, a stable pH between 6 and 7, and a minimum supply of nutrients.
    Premium fast-draining soils with good texture that will not break down quickly are the best choice. Potting soils found at nurseries are often formulated with a wetting agent and retain water and air evenly, drain well, and allow easy root penetration. Organic potting soils are very popular. These soils are often fortified with organic nutrients including readily available high-nitrogen worm castings. Potting soils are very heavy, and transportation costs tend to keep them somewhat localized. There are many good brands of high-quality potting soil. Ask your nursery person for help in selecting one for fast-growing vegetables.

Quality potting soil

Quality organic potting soil

Mushroom Compost
    Stay away from discount brands of low-quality potting soil. These soils can be full of weed seedand diseases, hold water unevenly, and drain poorly. Ultimately, saving a few pennies on soil will cost many headaches and a low yield later.
    Many potting soils supply seedling transplants and clones with enough food (fertilizer) for the first two to four weeks of growth. After that, supplemental fertilization is necessary to retain rapid, robust growth. Add fine-grade dolomite lime to buffer and stabilize the pH. Trace elements in fortified soil and soilless mixes can leach out and should be replenished with chelated nutrients, if deficiency signs occur. Organic growers often add their own blends of trace elements in mixes that contain seaweed, guanos, and manures.
    Although some growers reuse their potting soil, I do not recommend it. If used for more than one crop, undesirable microorganisms, insects and fungi start growing; nutrients are depleted; water and air retention are poor, causing compaction and poor drainage. Some growers mix their old potting soil with new potting soil to stretch their mix. Cutting corners this way most often costs more in production than is saved in soil.
    Potting soil or soilless mix that contains more than 30 percent lightweight pumice or perlite may float and stratify when saturated with water before planting. Mix water-saturated soil thoroughly with your hands until it is evenly mixed before planting or transplanting, if necessary.
Mushroom Compost
    Mushroom compost is an inexpensive potting soil and soil amendment that is packed with organic goodies. Mushroom compost is sterilized chemically to provide a clean medium for mushroom growth. After serving its purpose as a mushroom growing medium, it is discarded. Laws usually require that it sit fallow for two years or more to allow all the harmful sterilants to leach out. After lying fallow for several years, mushroom compost is very fertile and packed with beneficial microorganisms. The high-power compost could also foster antifungal and antibacterial properties in foliage and below the soil line, which helps guard against disease. Mushroom compost is loaded