Premium Potting Soil Mix Ingredient Ratios

If you are only filling a few pots, buying premixed soil is probably the way to go. But if you are starting your own seedlings or planning a container garden, mixing your own potting soil can save you a lot of money. Making your own also allows you to tailor the mixture to your needs or to include only homemade ingredients.

Seedlings perform best when started in a soilless mix. Cornell University suggests mixing soilless potting medium according to the following recipe: three 3.8 cubic foot bales of peat moss, two 6 cubic foot bags of vermiculite, 20 pounds of dolomitic limestone and 6 pounds of 11-5-11 fertilizer. This yields about 1.2 cubic yards of potting medium. The amounts for a third of the recipe would be one bale of peat moss, three-quarter bag of vermiculite, 7 pounds of lime and 2 pounds of fertilizer.

Some seedlings do fine in the soilless mix until planted in the garden, but you need to hold others until temperatures are warm enough and frost is not a danger before you can plant them. In that case, add some compost to the mix and transplant into a larger pot. A good basic mix for vegetables is one part each of peat moss, perlite or vermiculite, compost, and garden soil or bagged topsoil. You can use any size container for measuring and mix all of the ingredients into a wheelbarrow or large bin. You can also add a handful each of dolomitic lime, soybean meal, rock phosphate and kelp meal and mix into the potting soil for added nutrition. All of these ingredients are available at a well-stocked garden center.

Annual flowers growing in containers are heavy feeders. If you start with a nutritious potting mix, you won't have to feed the flowers all summer. Mix together one part each of expanded slate, composted chicken manure, worm castings, composted pine bark and coarse river sand. Expanded slate is sometimes called expanded shale and it helps to loosen heavy clay soil. The chicken manure and worm castings contain high amounts of nitrogen and the pine bark adds fertility as it decomposes throughout the season.

Some gardeners object to using ingredients mined and shipped long distances, such as vermiculite or perlite, or are of limited quantity, such as peat moss. With a little planning you can create potting soil from entirely homemade ingredients. Mix together equal parts of finished compost, leaf mold and well-aged saw dust (do not include treated wood). This mixture is fine for transplants or filling containers, but if you are starting seedlings, you should pasteurize the compost. Bake the compost at a temperature of 160 degrees Fahrenheit for an hour or 180 degrees Fahrenheit for 30 minutes. Use a meat thermometer to determine the temperature, and do not let the soil go over 190 degrees Fahrenheit.