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Foliar feeding: fertilizing plants through leaves instead of roots.

Yellowing leaves--chlorosis--can be one of the most frustrating maladies that a gardener faces. The cause may be too much sunlight, but it usually is a lack of available nutrients in the soil. And sometimes, no matter how diligently you apply fertilizers to the soil, a plant still won't green up.

If your plants have this problem, try spraying diluted fertilizer on the leaves. Done properly, foliar feeding is the fastest and sometimes most efficient way you can supply nutrients to a plant.

Which plants to spray

Most plants respond well to foliar feeding, to varying degrees. It's especially effective with azaleas, gardenias, rhododendrons, roses, flowering annuals and perennial, most vegetables, and citrus and apples. Commercial gardeners often use it on nursery plants, including small-needled evergreens.

Container plants, which frequently look chlorotic because watering has leached nutrients from the soil, are also idea subjects for foliar feeding. The quick green-up you'll get is especially appreciated with highly visible potted plants indoors and on decks and patios.

Foliar feeding can also get transplants off to a strong start.

In general, actively growing plants will show the best response. But remember that folair fertilizing is not a substitute for normal soil feeding. Consider it a useful supplement, especially when certain soil or weather conditions prevent the normal uptake of nutrients by plant roots. In early spring or late fall, for example, cool soil often restricts the availability of nitrogen and phosphorus in the soil, even though air temperatures are high enough for plant growth.

By feeding some plants through their leaves at these times, when soil feedings are not as effective, you can correct many nutrient deficiencies. Foliar feeding also allows you to help meet a plant's nutrient needs without watering the root zone--an advantage during rainy seasons when plants don't need water. At any time of year, alkaline soil (high soil pH) can render some micronutrients unavailable to roots of acid-loving plants, causing chlorosis. Foliar application of fertilizers containing micronutrients, especially iron, can often correct this type of yellowing.

(In this situation, consider foliar feeding a temporary answer. For a longer-lasting solution, begin adjusting soil pH by using acid-type soil fertilizers, acidic mulches, or soil sulphur, and by applying iron chelates to the roots as needed.)

What to buy

At the nursery or garden supply center, you probably won't find foliar fertilizers sold as such--although one such product is becoming more widely available.

Look for liquid or water-soluble plant foods that give label directions for foliar feeding--usually 1 tablespoon or 1 ounce per gallon of water. In most cases, the rate of dilution specified is the same as for soil feeding.

Or simply choose a fertilizer with nitrogen in urea form and micronutrients such as iron, zinc, and manganese. As a precaution, start with half the amount recommended for feeding the roots.

How to use it

Before you do any spraying, make sure the plants are not suffering from lack of water; dry plants may absorb the foliar spray too quickly, possibly burning the leaves.

The easiest way to foliar-feed is to use a hose-end sprayer. (Be sure sprayer or hose bibb is equipped with antisiphon device.) Early mornings and cloudy days are good times; avoid hot or windy weather. Keep the spray from hitting walls, outdoor furniture, or surfaces that will stain.

Completely soak the plant to the drip-off point, making sure to wet both upper and lower leaf surfaces. Runoff can be used by the roots. Any irregular greening or spotting should disappear with a second application.

For best results, spray at least three times at 10-day intervals. Frequent light applications are much more effective than one strong dose.

Resist the temptation to overdo it: too much nitrogen can reduce yields of some fruiting plants, and many nutrients can burn leaves if applied excessively.
COPYRIGHT 1986 Sunset Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1986 Gale, Cengage Learning. All rights reserved.

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Date:Mar 1, 1986
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