Potting soil is different than soil-less potting mix, which is used to germinate seeds. Several years ago, I started blending my own potting soil, and you can, too.
The best homemade potting soil mix has three basic ingredients:
1) a growing medium
2) something to help retain moisture and nutrients
3) something to promote drainage
- A growing medium, such as garden soil from a home and garden center, which has been pre-sterilized to remove weeds/disease.
- Spaghnum peat moss for moisture retention. It is harvested from bogs that have been drained, so the moss has dried and turned a light brown color; you may need to lightly moisten before mixing the potting soil.
- Perlite, vermiculite, or sand for drainage. Perlite is made by heating bits of a glasslike mineral until they expand into puffy, lightweight particles. It holds no water, aside from the little that clings to the surface of each particle. Don't use playbox sand, it's too fine, look for a course sand.
Mix those three ingredients in equal proportions, adding more of any ingredient until you have a loose but clump-able mix. Keep this mix in a covered storage container. I use a large galvanized garbage can.
Remember, while homemade potting soil is a great growing medium, your plants won't thrive unless you regularly add fertilizer to the the potting soil. 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 which is what I use. You can also rely on a fertilizer that offers slow-release nutrients in order to help your plants retain their growing vigor.