Fertilizer: It's how your garden grows

Wednesday, February 8, 2006
Left to right: rose food, azalea food, soluble plant food (powder), root feeder system, plant spike, granular tree and shrub food and spike system refills. (Don Frazier)

When gardeners grow roses, they fertilize with a rose food that is specifically designed to produce vigorous bushes with lots of blooms. Azalea gardeners not only want a fertilizer that produces vigorous bushes with lots of blooms, but they also want a fertilizer that keeps the soil "pH" acidic. In both cases these gardeners look for a special rose food or an azalea food on the market.

Unfortunately gardeners tend to forget about fertilizing standard foundation landscape shrubs such as pine, yew, spruce, boxwood and such standard shade trees as oak, hickory, or maple. So should you fertilize these foundation plantings? Of course you should. If you want these plants to thrive instead of just survive, fertilize them every year.

The fertilizer you use should be one similar to 19-8-10 with micro-nutrients. Notice, the nitrogen to phosphorous ratio favors nitrogen. For most foundation landscape plants you want good shoot and foliage growth. Therefore use a fertilizer high in nitrogen, the nutrient that promotes foliage development.

Micro-nutrients are important because many landscapes are planted in new developments, where native soil has been moved, turned, or removed. Poor soils often are deficient in micro-nutrients.

Make sure that the nitrogen source is primarily from urea or nitrates, and not from ammoniacal products. This will ensure that the pH of the soil will not change due to fertilizer. Acidic fertilizers used for azaleas contains mostly nitrogen from ammonia derivatives.

When applying fertilizer place it near the drip line of the tree or shrub being fertilized. The drip line is below the end of the branches farthest from the main stem of the plant or shrub. The highest concentration of feeder roots is near the drip line.

Most of the feeder roots of a tree or shrub are in the top 12 inches of the soil. Therefore if you place fertilizer deeper than 12 inches below the soil, most of it will be lost to leaching. Apply fertilizer at or just below the soil surface.

There are many forms of tree and shrub fertilizer on the market. I prefer to use a granular product and spread it evenly on the ground with a lawn fertilizer spreader. I get the job done quickly, and place the fertilizer on the soil surface where it can be watered in, either by Mother Nature or with a garden hose.

You can also purchase tree and shrub fertilizer in the form of stakes. These stakes are driven into the soil with a hammer. They should be placed at or near the drip line. Be sure not to drive the stakes too deeply into the soil. You don't want the fertilizer placed below feeder roots.

The high concentration of fertilizer in one spot may have the tendency to burn tree or shrub roots near the fertilizer stake. Sometimes you will also see tuft of grass growing rapidly under a tree fertilized with stakes.

The company Ross makes a root feeder that attaches to the garden hose. Specially formulated fertilizer spikes are placed inside the root feeder. As water moves through the feeder, some of the fertilizer dissolves and is carried into the soil through the feeder. Just be sure not to introduce the fertilizer below feeder roots.

You can also fertilize your trees and shrubs with a soluble powder fertilizer. Just mix the powder with water and spray it through a calibrated applicator or through a siphoned mixer. Most of the nutrients will be taken up by plant roots, but some fertilizer will be absorbed by plant fertilizer.

Apply fertilizer just before trees and shrubs begin their spring flash of growth. Therefore make your application sometime in March or early April. I would also make another application in late summer to provide nutrients needed for the onset of winter dormancy.

If you want your foundation plantings to thrive just like your roses and azaleas, give them timely applications of fertilizer. They will thank you for it.

Send your gardening and landscape questions to Paul Schnare at P.O. Box 699; Cape Girardeau, Mo. 63702-0699 or by e-mail to news@semissourian.com.

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