Soilless potting soil is any type of plant media product that does not contain your normal type of dirt. Most gardening experts define soilless potting soil as dirt that does not contain conventional soil at all.Instead it consists of a mix of ingredients: sphagnum peat, compost, perlite and vermiculite.

soilless potting soil

What Is Soilless Potting Soil?

Soilless mixtures tend to be looser than regular potting soils. This makes them a good choice for planting that requires good drainage, such as container gardening. Also known as sterile mixes, soilless potting soil is ideal for starting seedlings. It reduces the risk of diseases against young plants, as well as the risk of soil with pH problems that may affect a young plant’s growth.

A Careful Mix of Ingredients

Each ingredient in soilless potting soil serves a specific purpose. The ratio of each ingredient can be adjusted to meet specific gardening needs. Four substances are typically included in soilless potting soil. The ingredients of soilless potting mixes vary, and can include fertilizers, as well as materials like bark or the coconut by-product, coir.

Sphagnum Peat

Sphagnum peat is decayed sphagnum moss, just one of a genus of hundreds of mosses commonly called peat moss. As a soil conditioner, sphagnum peat increases the soil’s capacity to retain water and nutrients, making peat a useful addition for areas with sandy soils.

Perlite

Produced by heating volcanic rock, perlite is a sterile substance that both increases water absorption and drainage. Perlite also improves the aeration of the soil, helping roots grow. Perlite can have a white, graveled appearance that resembles shredded Styrofoam.

Vermiculite

A naturally occurring mineral, vermiculite serves the same function as perlite, but retains more water. It appears as silver grey flecks. Until the 1990s, some vermiculite contained harmful asbestos. Vermiculite that is exposed to the mineral diopside over long periods of time can turn into asbestos. Vermiculite mines worldwide are now regularly tested for asbestos.

Compost

Compost is a mix of decaying organic matter like dead leaves and manure. Composted materials adds nutrients gradually to the soil as the substance further decays. It also improves the overall structure of the soil. When purchasing soilless potting mixes, it is important to read the list of ingredients carefully. Low-quality compost can contain sewage sludge. Looking for a mix with a description that includes “aged forest products” can ensure you’re getting a quality compost. Quality compost will be even in texture, absent of large chunks of wood or bark.

When to Use A Soilless Potting Soil

Soilless potting mixes are the premium choice for nearly every planting application. Using a quality soilless mix the best way to ensure that your planting will be free of contaminates like bacteria, insects and seeds. It is also the best way to ensure a proper mix of drainage, water and nutrient retention, aeration and soil structure. The wide variety of soilless mixes available makes it possible to adjust formulas for every planting situation.

Starting Seedlings

Soilless potting mixes are especially suited for certain types of plantings, such as starting seedlings. A plant is at its most vulnerable during the first few days and weeks of its life, and a sterile soil mix offers seedling the best chances for success.


Container Gardening

In a garden, gravity pulls water and nutrients through the soil. In container gardening, gravity needs a bit of help. Plants grown in pots need soil that is neither too soggy nor too dry. Soilless potting mixes provide the best way to achieve this balance.

Plant Specific Needs

Certain types of plants in the garden also require a careful balance between too wet and too dry. Succulents and cacti, which are tolerant of dry conditions, prefer soilless mixes and flourish best when good drainage includes valuable nutrients.