Last updated on May 7th, 2012
THE ART OF SOIL-MAKING can be surprisingly simple or unnecessarily complicated. I prefer the easy approach. After all, most potted plants are hardy enough to thrive in any formula that holds moisture (but not too much) and contains gritty matter for drainage and root-aeration. My own plants prosper in various adaptations of this old-fashioned, but tried-and-true mixture:
One part well-worked garden soil
One part leaf mold (or compost)
One part sand
My nifty soil-sifter
Next, the sifted soil is poured into a roasting pan, sprinkled lightly with water, covered with a lid and baked for exactly one hour in a 180-degree oven. The goal is not to sterilize the soil, which would render it inert, but only to pastuerize it. Thus, nutrients are preserved, while weed seeds, insects and harmful pathogens are eliminated. Contrary to what you may have heard, soil does not emit an unpleasant odor as it bakes.
Leaf Mold – This is the soft, crumbly substance that results after autumn leaves are saved in a pile, moistened regularly, and allowed to decay for at least two years. The best leaf mold for houseplants is always found at the bottom of the pile. This, too, must be sifted and pasteurized in the same manner as for garden soil. I can’t imagine gardening without leaf mold. It is far superior to peat moss in terms of both nutritional value and moisture-retention.
Compost – If you have a compost heap, you can use this rich, nutritious material for your houseplants. Gather some of the most decayed produce from your pile, then sift and bake it.
Sand – This is the gritty matter that lightens and introduces pockets of air to the potting mix. I use coarse builder’s sand, not seashore or playbox sand. Builder’s sand is available at most hardware and building-supply outfits, but only in enormous quantities. If you don’t wish to have a heavy sack of sand in your house, you can always substitute perlite. Perlite is a volcanic mineral that forms porous white granules when exposed to high heat. You can buy it in small quantities at almost any garden center.
I like to keep my soil components in separate, air-tight containers. Then, when soil is required, I can withdraw the approximate quantities I need and blend them by hand in a large bowl or dishpan.
It is wise to vary the basic soil mixture for certain plants. African violets and ferns, for instance, prefer a light, woodsy formula. For them, I increase the amount of leaf mold and reduce the sand. Azaleas and citrus plants like an acidic soil, so I add to the basic mix either a handful of composted oak leaves, or humus gathered from beneath my arborvitae hedge. I give my geraniums and herbs soil, leaf mold and sand in equal parts.
Learning to make potting soil is no different from learning to cook without a recipe. One has to experiment with the ingredients and adjust their proportions until the concoction seems “just right.” Remember that most plants aren’t overly fussy about soil. If your mixture holds moisture and drains well, you’ve essentially hit the jack-pot.
Houseplants do not require a diet of expensive, peat moss-based potting formula anymore than a child requires a diet of cheez-whiz. When we make our own potting soil from sustainable substances, our planet, plants and purses all benefit. Won’t you give this soil-making venture a try?
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