Houseplants depend upon you for all their needs. A good potting soil goes a long way toward supplying them with the nutrients and water necessary for their survival. The best potting mixes retain both moisture and nutrients without compacting around the roots or becoming soggy and waterlogged. Making your own homemade potting soil recipes is less expensive than commercial mixes, and you can be assured that the ingredients are good for your plants.
Soil mixes contain sterile garden soil along with other amendments. Soil must be sterilized before use--otherwise disease organisms and weeds may be present in the mix. Soil mixes are best used on established houseplants. Avoid using them for seeds; they are heavy, and the seedlings have trouble breaking through the soil mix surface.
Purchase sterile garden loam or soil from a garden center or make your own. Spread garden soil in a roasting pan and cover it with foil. Bake it at 280 degrees for 30 minutes to sterilize. Mixed the sterile soil with equal parts peat moss and vermiculite. The peat retains moisture in the soil without becoming soggy while the vermiculite adds aeration around the plants' roots and helps retain nutrients in the mix. Both are available at garden centers.
Soil-less mixes contain no garden soil or loam. They are well-suited for planting seeds but can be used for most plants that require well-drained conditions. The mix is also lighter, making it a good choice for large planters because it helps reduce weight.
To make a soil-less potting mixture, combine equal parts peat moss and vermiculite, or perlite if desired. Perlite is similar to vermiculite and is also available at garden centers. Break up any chunks in the peat moss if you are starting seeds in the mix, keeping the texture of the potting mix as fine as possible. You can also combine equal parts sterile compost, peat moss and vermiculite for a soil-less mixture that has some nutrients in it. Both mixtures must be pre-moistened before use or will dry out quickly.
While there are some nutrients in soil-based mixes, soil-less mixtures depend completely on outside fertilization. Both require fertilization in order to grow houseplants long term. You can use a weekly application of houseplant feed or add a slow-release fertilizer to the soil before planting.
To make a fertilizer mix for your potting soil, add 4 tablespoons of dolomitic limestone to a bushel of homemade soil. Mix in a slow-release, balanced fertilizer at the rate recommended on the fertilizer label. Combine it all together before planting. More fertilizer will be needed within two to three months. You can either add more slow-release fertilizer to the soil using the label recommended rate or begin fertilizing with a soluble plant food.