Methods of Application

Fertilizers can be applied either directly or indirectly to plants. When turf is fertilized, tree and shrub roots that extend into the turf area absorb some of the fertilizer, and are therefore indirectly fertilized. Turf fertilization rates should be supplemented only if trees and shrubs are showing symptoms of nutrient deficiency.

Direct application of fertilizer may involve incorporation into the backfill soil or placement in the planting hole at planting time. However, the most common form of direct fertilizer application, broadcasting, is generally the most effective, especially relative to cost. Simply placing the desired fertilizer over the soil atop the tree and shrub roots and watering it in is usually adequate. Compacted soil should first be aerated or raked.

The most sensible and efficient way to fertilize large trees is to scatter granular fertilizer on the surface of the soil and allow rain or irrigation water to transport the nutrients to the roots. Evenly broadcast the fertilizer over the area to be fertilized - that area covering the outer two-thirds of the distance between the trunk and the drip line and extending at least 50 percent of the crown radius beyond the dripline.

Another method is to put granular fertilizer into holes in the soil that are 4 to 12 inches deep. These holes are dug in a regular pattern at 2- to 3-foot intervalsl, in the same area as broadcast fertilizer is applied. Divide up the fertilizer among the holes. This technique does not insure consistent coverage to all feeder rootsl, especially in the upper few inches of the soil surface where the majority of the roots occur. High concentrations of fertilizers in these holes can also injure roots located bordering the hole.

A commonly used commercial method is to inject liquid fertilizers into the soil. A special injection rod is used and the fertilizer solution is injected under pressure. A comparable probe mechanism called a 'root feeder' is sold at most garden centers. The long probe attaches to a garden hose and water-soluble fertilizer cartridges distribute nutrients and water directly into the tree root zone. The tip of the injection needle should be inserted 4 to 12 inches into the soil at 2- to 3-foot intervals. Fertilizers suitable for liquid injection are typically more expensive per unit of nutrient and are frequently more difficult to apply than granular fertilizers.

Spikes are another alternative for tree or shrub fertilization. These are pounded into the soil with a heavy hammer and can only be used successfully when the soil is moist. The spikes do not evenly distribute fertilizer around the tree's or shrub's major feeder roots. These spikes are an expensive alternative. Their reputation is based on simplicity and ease of application.

Foliar feeding is a short-run answer when a nutrient inadequacy has been diagnosed. The leavesl, buds and green wood are able to absorb some nutrients. Foliar nutrient sprays are put on with a pressure sprayer or siphon sprayer attached to a garden hose. The green-up from foliar spraying is fairly speedy but not long enduring. Generally deficiencies of micronutrients including ironl, boron or manganese are rectified by seasonal foliar applications.

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