Sphagnum peat moss is a stable organic material that holds 15 to 30 times its weight in water and decomposes very slowly. It contains about 1% N but little is released because it breaks down so slowly. It has a pH of about 4 so lime must be added to the mix with sphagnum peat, at the rate of 8.5 lb. per cubic yard of peat to neutralize the acidity.
Coco Coir comes from coconut husks and is a waste product of the coco fiber industry. It has physical properties much like peat but a higher pH of about 6. It holds up to nine times its weight in water. It can have a high salt content. It comes in compressed blocks that must be soaked in water for several hours or overnight before mixing with other ingredients.
Lime is either calcitic (high calcium) or dolomitic (high magnesium) both are used to increase the pH of a mix but dolomitic lime is preferable for supplying both Ca and Mg.
Vermiculite helps hold water and fertilizer in the potting mix, and it also contains some calcium and magnesium. It has a pH near neutral. Vermiculite comes in different grades; medium grade is usually used for starting seeds, a coarse grade may be used for larger plants.
Perlite is a volcanic rock that has been heated and expanded. It is lightweight, sterile and has a neutral pH. It can be used to reduce the weight of a potting mix and increase its aeration and drainage.
Mycorrhizae Fungi colonize the root system of a host plant, providing increased water and nutrient absorption capabilities while the plant provides the fungus with carbohydrates formed from photosynthesis.
Most commercial grow mixes have the proper ratio of ingredients plus wetting agents and may contain Mycorrhizae Fungi and fertilizer - check package label for ingredients.
