Planting seeds properly is the first step toward growing a healthy plant. Water, light, oxygen and temperature all affect seed germination. In addition to these factors, using the appropriate media or planting material will affect seed germination. To germinate properly, seeds need a medium that is loose, fine and uniform. Proper aeration is required as well. Finally, the medium should be sterile and not contain weed seeds, insects or diseases.
Vermiculite is an inorganic soil amendment consisting of a type of clay. Vermiculite holds water, nutrients and air because of the folded molecular structure. Vermiculite is used instead of perlite in soil mixtures if more water retention is required.
Garden soil, an organic component of seed germination medium, can be purchased already sterilized. If this type of soil is not used, ordinary soil can be sterilized by being heated to 180 degrees Fahrenheit for a half hour in an over set at 250 F. This process creates unpleasant odors; an oven bag can help reduce these odors. Do not overheat the soil because overheating can cause soil damage. To keep the soil sterile, tools and containers used for seed germination should be washed thoroughly and rinsed in a 1-9 ratio bleach and water solution before use with sterile soil.
Sand is an inorganic soil amendment that improves drainage and aeration. Too much sand can make containers heavy--care should be taken to avoid this. Sand should not be mixed with clay soil. Most often, the same kind of sand as that used in construction can be used for seed germination.
Perlite is another inorganic soil amendment that holds air and provides drainage. Unlike vermiculite, perlite does not retain water. Perlite can be used instead of sand, but it is more expensive. Perlite is made from heated fluoride-based volcanic rock. Unfortunately, it tends to float to the top when the medium is watered. Perlite must be watered before adding to an amendment mixture to reduce the possibility of inhaling harmful perlite dust.
Sphagnum peat moss, an organic soil amendment, has natural antifungal properties. It also helps to retain water. Sphagnum peat is acidic, so it can help if you're trying to grow a plant that requires acidic soil. Sphagnum peat grows in bogs in the northern regions of North America. It is low in salts. The coarse texture of sphagnum peat helps with aeration. Too much sphagnum, however, can cause too much water retention. Be sure to moisten peat before adding it to other materials.