Fertilizing Landscape Trees and Shrubs Part 4

Fertilizer Placement

Fertilizer should not be concentrated around the base or trunk of a tree or shrub, but should be applied over as much of the plant's root zone as possible. For trees and shrubs, fertilizer should be applied over an area twice as large as the crown spread. Since most landscape plant roots grow in the top foot of soil surface, but not deep application, is recommended.

How Fertilizer Uptake is Affected

Many factors affect how well and well trees and shrubs absorb fertilizers. The most important uptake factors are:

Fertilizer form (inorganic, fast release, or liquid forms are absorbed faster than organic, slow-release,or dry forms)
Soil type (clay particles and organic matter soak up or bind more nutrients than sand, so fertilizer application needs to be more often in sandy soils, but with lower rates each time due to leaching potential)
Soil moisture content and soil warmth (nutrient uptake is faster in moist warm soils)
Plant vitality (plants under stress are less able to take up available nutrients due to damaged or reduced root systems)

Timing of Application

Fertilizer should be utilized when plants require it, when it will be most efficacious, and when plants can readily accept it. Late summertime and early autumn fertilization may hasten new growth that is not winter hardy, and summer drought could interfere with nutritive uptake, but spring, fall, and wintertime applications are satisfactory. A split application might be advantageous, applying half the annual rate in early spring and the balance in the fall as or after plants go dormant.

If water is unavailable, don't fertilize altogether - plants will be unable to assimilate the nutrients. (During a dry time of year, fertigation - application of fertilizer by means of an irrigation system can be beneficial.)

Tree and bush fertilization comprises only one part of aggregate plant maintenance. Fertilization might not benefit a plant if it's under stress from inadequate soil aeration or drainage, sodden soil, deficient light or space, or excessive pest problems. Altogether factors determining plant growth should be kept at optimal levels to guarantee plant vigor.