Success with your own soil - potting soil recipes - Garden Basics

Flower & Garden Magazine, Dec-Jan, 1994

THE NATURE OF THE SOIL IN YOUR yard was determined centuries ago, by geologic forces at work in your area -- unless, of course, building contractors changed it radically by scraping the native soil away, dumping fill over it, or similarly altering it.

Since the soil in your garden, lawn or even indoor containers largely determines the success you will have with your plants, it is important that you know something about it.

Essentially, soil consists of mineral particles formed by the disintegration and decomposition of rock over the ages. The way these particles were mixed, moved and deposited by various natural events (glaciers, floods, dust storms, upheavals) determines today's different soil types. Differences in the mineral components set apart the various textural groups of soil: gravels, sands, silt and clay. How these minerals settled together created a soil "profile" that may vary widely, even in the same neighborhood. If you want to inspect this profile, just dig a deep, smooth hole and look at the side of it.

There's more to a soil than just minerals, however. Your soil also reflects what has happened to it in other ways -- the kind of plants that have grown up and then died in it, the freezes, fires, pressures and even, perhaps, the animals (including humans) who have lived in or over it.

The dark color of "good" soil usually (but not always) comes from humus -- the remains of vegetation. In cultivated soils of humid temperate regions, humus may make up five percent of the soil's volume. In sandy soils of hot, dry areas, there may be hardly any humus at all. Then, too, moist soils are inhabited by an infinity of tiny creatures -- bacteria, fungi, and others that play a part with their acids and enzymes in changing the hard minerals into soluble ones plants can absorb. Soil is not a dead, static thing, but rather a living, breathing and evolving one.

A great variety of ready-mixed potting soils for indoor plants or for starting seedlings indoors to later transplant outdoors in the garden are available in the marketplace. However, you can easily make your own soil mix for container gardening or seed starting. Some long-time readers of FLOWER & GARDEN magazine swear by the results from this soil mix "recipe."

Indoor Soil Mix

This mix is lightweight for seed starting, window boxes and potted plants where you do not want much weight. The "recipe" follows a formula used by commercial growers. Eventually the nutrients will be exhausted, so plants grown in this soil mix will need occasional feeding with a soluble fertilizer.

Makes 1 bushel.

1/2 bushel (4 gallons) vermiculite

(horticultural grade)

1/2 bushel (4 gallons) shredded

sphagnum peat moss

4 T. 20% superphosphate (powdered)

8 T. ground limestone (or calcium

carbonate)

Either one (but not both) of the

following:

6 T. 33% ammonium nitrate or

1 C. 5-10-5 fertilizer (or as close to this

formulation as you can get)

Thoroughly mix dry ingredients in a large tub. Store dry in a plastic or wood container. Moisten a few hours before using.

Soil Mix For Acid-Loving Plants

Azaleas, camellias, rhododendrons and gardenias require special soil conditions. This acidic mix should give them a good start.

Makes 1 bushel.

1 bushel shredded sphagnum peat

moss (can be mixed with part

redwood shavings)

1/4 oz. (1 t.) potassium nitrate

3/4 oz. (4 t.) 20% superphosphate

(powdered)

2 oz. (3-1/2 T.) dolomite

3-3/4 oz. (6 T.) ground limestone (or

calcium carbonate)

Thoroughly mix dry ingredients in a large tub. Store dry. Has a pH of about 5.7 depending on the quality of the peat.