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GARDENING

Potting Soil Separates Winners From Losers

March 21, 1998|From Associated Press

Potted plants--including garden transplants and houseplants--grow poorly in garden soil, even good garden soil, if used alone. What these plants need is potting soil, whose basic ingredients might include garden soil plus mineral aggregate and organic matter. Once you are familiar with the basic ingredients of potting soils, you may want to make your own.

Mineral aggregates keep potting soils aerated and ensure that water flows readily into the mix, through it and out the bottom of the container.

Mineral aggregates include vermiculite, a type of mica, and perlite, a volcanic rock that has been popped at high temperatures. Both lightweight materials are available at garden centers.

Use sand as mineral aggregate when you need a potting soil with more weight--for example, to keep a top-heavy jade plant from toppling. Potting mixes made with sand are also good for cactuses and other succulents because they stay drier than those made with perlite or vermiculite. Use sand with large size particles, sold as "quartz builders" sand.

Organic matter in potting soils holds water in reserve for plants. Good choices include peat moss and sphagnum moss, both available in stores. Compost and leaf mold are organic materials you can brew yourself.

Potting mixes made with garden soil are sold commercially, but you can make one yourself by sieving together equal volumes of peat moss and perlite.

Because the mix has no garden soil or compost to supply nutrients, add one-half cup of dolomitic limestone, 1 tablespoon of 28% superphosphate (or 2 tablespoons of bone meal) and one-half cup of 5-10-5 fertilizer to each bushel of final mix.

Even if you buy potting soil, keep some type of mineral aggregate and organic material on hand. If the mix seems too dense, or if it is for a succulent plant, add extra aggregate. Begonias and African violets, on the other hand, like constantly moist soil, so add extra peat moss or other organic matter to their potting soils.

Traditional potting mixes contain real garden soil. Make up this mix by combining equal parts garden soil, peat moss, perlite and compost. Supplement the nutrients in the garden soil and compost by adding, for each 8 gallons of potting soil, a cup of lime and a half-cup each of bone meal and cottonseed meal. Mix thoroughly, then rub the mix through a one-half-inch sieve.

If you include compost or garden soil in your potting mix, you may have to pasteurize it to eliminate pests. Fill a baking pan with potting soil, bury a potato in it, and bake in a medium hot oven. When the potato is baked, the soil is ready. Pasteurization is not necessary if you use healthy garden soil and compost that has decomposed sufficiently to eliminate pests.

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