Providing healthy, disease-free soil is vital for a successful greenhouse, whether you have a small backyard structure or a larger commercial venture. Not any soil will do. Greenhouse soil must provide proper drainage while still supporting plant roots. Proper nutrition also is vital. Though most greenhouse plants are frequently fertilized, proper soil acidity and the base nutrients still are necessary. Creating your own soil mixes also costs less than purchasing commercial greenhouse soil mixtures.
Sterilize the garden loam if you are using loam from the garden and not purchased, pre-sterilized loam. Place the loam in large roasting pans and mist it with water until it is moist. Cover the pan with foil, then bake the loam for 30 minutes at 200 degrees Farenheit. Allow the loam to cool completely before use.
Combine one part loam with one part of moistened peat moss, which helps retain proper moisture in the soil. Substitute compost for the peat if desired, though compost does not drain quite as well.
Mix one part of perlite or coarse builder's sand with the loam and peat mixture. Perlite or sand adds drainage to the mixture. Combine all three ingredients thoroughly.
Perform a soil pH test according to package directions. Add the amount of dolomitic limestone recommended on the test to raise the soil pH to between 6.0 and 7.0.
Add a slow-release fertilizer to the greenhouse soil prior to use if you are not beginning soluble fertilizer treatments right away. Use a fertilizer formulated for the type of plants you are growing. Mix the fertilizer with the soil at the rate recommended on the label.