Plants depend on good soil to grow, and creating your own potting soil gives you control over the ingredients so you can ensure the best growing medium for your plants. Whether you are starting seeds, growing vegetables or making soil for houseplants, the right ingredients ensure a soil that remains moist without becoming easily waterlogged.
Potting soil ingredients must provide structure for the plants to root within and also supply proper drainage while still retaining enough moisture for proper growth. Garden soil or compost becomes too dense when used alone, which prevents drainage and aeration. You can combine the soil with sterile peat, which allows better drainage and prevents compaction. Coarse sand, vermiculite and perlite also aid drainage and aeration. Soilless mixes don't contain any garden soil and only use compost, peat, shredded bark, vermiculite and other soilless ingredients.
Compost and garden soil both require sterilization to kill any pathogens or insects present. Peat, vermiculite and other nonorganic ingredients are usually sterile so they don't require any pretreatment. Sterilize compost and soil in a disposable roasting pan. Baking the moistened soil for about 20 minutes at 200 degrees Fahrenheit, so the soil reaches a temperature of 180 degrees throughout; this kills most pathogens. Allow the soil to cool completely before adding it to the potting soil recipe.
A suitable soil medium contains equal parts garden soil or compost, peat, and sand, perlite or vermiculite. A soilless mix contains equal parts peat and vermiculite or perlite. You must mix the ingredients thoroughly so they are evenly incorporated together. Soil mixes contain some nutrients, while sterile soilless mixtures are usually nutrient-free. Mixing in 1/3 cup of a slow-release, all-purpose fertilizer per each quart of mixed medium provides some nutrients for initial growth. Further fertilization depends on the type of plants you are growing.
Use and Storage
The potting medium requires proper storage if you are using it immediately. Storing it in a sealed container keeps it sterile and prevents pests from invading the mix. You must thoroughly moisten the potting mix before you use it. Peat absorbs water slowly, so moistening the mix 30 to 60 minutes before planting allows the medium to absorb sufficient moisture while any excess has time to drain from the bottom of the pot. Soilless mixes tend to dry more quickly than those containing compost or soil, so they will likely require more frequent watering after planting.