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The Plant Seed - Germinating and Starting Indoor © 2006

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Soils and Mediums for Starting Seed Indoor © 2007

Soil to start seeds indoors should have several qualities. It should be sterile, hold moisture, and be fine enough for the seeds to emerge from and send roots into. Sterility is important because of the danger of diseases like damping off wiping out young seedlings. Constant moisture is needed to keep the germinating seeds from drying out. Once the germination process has started, seeds allowed to dry out will die. A fine texture is important to allow seedlings to emerge from the soil unhindered.

There are several different types of soils availble commercially that fit the bill. You will find fine ground vermiculite, seed starting plugs, peat mixes and rock wool. The advantages and disadvantages of each will be explored in the remainder of this article.

Vermiculite is a common seed starting medium found at garden supply centers.' It is a mineral which is quite abundant in Montana and North Carolina. The mineral is heated after extracting which causes it to expand. Vermiculite is an ideal material to use for starting seeds indoor, as it absorbs water, is sterile, and lightweight. It also contains two important plant nutrients, potassium and magnesium.

Vermiculite is often used in potting soil mixes. The Number 4 mix is the best used for seed starting as it is extremely fine. The heating process used to manufacture it kills any microbes which may be in it, so no soil borne diseases will be introduced by using it. Vermiculite is also used in construction as an insulation. Construction grade vermiculite is treated with chemicals and should not be used to grow plants indoors or elsewhere.

Sphagnum moss has its origins in bogs and is the dehydrated remains of plants. It is lightweight, sterile and will hold ten to twenty times its weight of water. It is used extensively in indoor potting soil mixes and also is the chief ingredient in peat pots. Milled sphagnum peat moss is a finely shredded material which is ideal for starting seeds.

Seeds started in milled sphagnum moss have a very high germination rate. Sphagnum peat also has fungicidal qualities which help prevent damping off. It has little nutritional value, so feeding of plants grown for any length of time indoors is necessary.

In addition to using milled sphagnum moss and vermiculite you will also find various potting soil blends for starting seeds indoors. These soils are usually composed of mixes of sphagnum peat and vermiculite with some slow release fertilizer mixed in. These types of soils combine the qualities of peat and vermiculite with the added bonus of plant nutrients to assist the seedling to make a good start.

Vermiculite, sphagnum peat, and soil mixes are the main mediums you will find to start seeds indoors. All three have their advantages and any of them will do a fine job of germinating seeds.

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