Soil is often contaminated with weed seeds, nematodes, fungi and bacteria that may cause plant losses. Commercial soilless mixes are made of peat moss, vermiculite, pine bark and other organic materials. They usually contain some added nutrients, are free of pests, and have good drainage and water-holding properties. Pure vermiculite is sometimes used for starting seedlings, but its fertility is low and plants will be stunted unless they are replanted soon after emergence. If transplants begin to develop a yellowish color, it may be necessary to use a small amount of a soluble fertilizer.
Soluble fertilizers are available from garden suppliers.
Various types of potting media are available from potting soils to soilless and hydroponic media. Regulating Light Seedlings will not need light until they emerge from the medium. Once they appear, transplants will grow better if they receive at least 6 hours of direct sunlight each day. Hotbeds, coldframes and small greenhouses are thus preferable to windowsills or basements of most homes. Too little light will result in plants that are small and spindly.