Topsoil consists of the top 1 or more inches of uncultivated soil. It is usually rich in organic matter, as this is where most plants both grow and die. Purchased topsoils are often sterilized with heat or steam, ensuring that no disease organisms or weeds seeds are present in the soil. Topsoil from your own yard needs to be sterilized prior to adding it to potting mixes to offer the same assurance toward the health of your plants.
Pour topsoil from your yard through a soil screen or a mesh window screen. This separates out rocks, roots and stems.
Place filtered topsoil in a roasting pan if it requires sterilization. Cover with foil and bake in a 200 F oven for one hour. Remove from the oven and allow it to cool to room temperature before using.
Mix 1 part of the topsoil with 1 part compost and 1 part peat moss. Compost manure can be substituted for the compost. Moisten the mix thoroughly prior to planting so the peat moss can begin absorbing moisture.
Mix a slow-release fertilizer with the topsoil potting mix. Choose a fertilizer that is formulated for the type of plants you will be growing. Although topsoil and compost have nutrients in them, they do not have all the nutrients required for healthy plant growth.