Growth medium is to create a stable base for your plants to grow through its roots and stop the weight of the cannabis plant. Over the years, many substances have been found to fill this role and they have different properties. Often a manufacturer will use one or more of these media, according to the methods he chose to culture and the desired properties of the medium in the container used.
Soil:
The soil is usually composed of rock, sand, clay and organic matter. Decomposed organic plant and animal matter and nutrients contained in the content of the clay soil binds together the soil and retain moisture, rocks and sand drainage holes in order to root oxygenation. In addition, the ground is working with the micro-organisms that feed on and degrade organic pollutants content.
If the growth of a potted plant indoors, you probably want at least mix with perlite to your soil to improve moisture retention. It is also strongly recommended that the compost used in a pan instead of soil you dug from the ground. A mixture of culture can be more carefully designed for optimal health of plants and outside the ground, will include many undesirable forms of insect life that can and will infect and kill your plants.
Another common problem with land is that the compost fertilizer is often already in them (in addition to the nutrients in the organic). In general, avoid soil nutrient release with time, but if you buy a bag, be aware that the cannabis plant does not need nutrients in a period of time and a little water with clean water to avoid burning the roots.

