Whether you use it with houseplants indoors, or for window boxes outside, potting soil is an essential element in any garden container. That's because potting soil is different than gardening soil: It is lighter and airier, so helps to keep water moving from top to bottom and keep plant roots as healthy as possible. Garden soil, on the other hand, moves water to the bottom and holds it there.
But pre-packaged potting soil can be expensive, particularly if you have lots of containers and flower boxes. Fortunately, you can make homemade potting soil quickly and easily with readily available ingredients.
Potting soil is different than soilless potting mix; the latter is used only to germinate seeds. The best homemade potting mixes have three ingredients: a growing medium, something to help retain moisture and nutrients, and something to promote drainage.
There are several recipes to make homemade potting soil. To closely mimic pre-packaged potting soil, you'll need
Mix those three ingredients in equal proportions, adding more of any ingredient until you have a loose, but clump-able, mix.
There's a second way to make homemade potting soil that involves fewer ingredients, and is favored by some organic gardeners. To make compost-based potting soil, simply mix equal parts sterilized garden soil and compost (pre-packaged or homemade); add sand or pebbles as needed to increase drainage.
Any potting soil will, over time, leach out nutrients that plants need. So while homemade potting soil is a great growing medium, your plants won't thrive unless you regularly amend the potting soil with fertilizer.
You can do this in a number of ways. You can amend your homemade potting soil mixture with limestone before using it. You can also top-dress plants occasionally with any number of types of compost, such as recycled mushroom compost. You can also rely on a fertilizer that offers slow-release nutrients in order to help your plants retain their growing vigor.