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Gardening with Henry Clay

Fertilizing trees

    Shade and flowering trees in your lawn are able to get some of their required nutrients from your lawn, provided the lawn is fertilized annually. However, the needed nutrients for shade and flowering trees in other parts of your garden or landscape are often ignored.
    No fertilizer is usually recommended or added at planting time. Limited growth and yellow foliage are evidence of this situation. A spring and mid-summer application fertilizer will benefit those trees that have been forgotten or neglected. Trees planted last year and those planted as recently as last fall should be fertilized this spring to promote new growth.
    Young seedling trees (under four feet) planted last year require only small amounts of fertilizer during this spring application. Surprisingly, a tablespoonful in spring and again during mid-summer will be adequate. Young trees 6-8 feet require approximately 3-4 tablespoons in spring and again by mid-summer.
    Apply fertilizer beneath and slightly beyond the spread of branches. Avoid applying fertilizer near the trunk of the tree as this can damage the roots. It is a good idea to water following an application of fertilizer as this puts the nutrients in solution and lessens the possibility of damage from fertilizer burn to new roots.
    Young shade and flowering trees greater than 2 inches in caliper and older established ones are usually fertilized on a square foot basis (area basis). This area is computed in a circle around the tree.
    To figure the square footage of this circular area to be fertilized around the tree, use the formula llR2 (area of a circle). First, measure the radius (R) in feet from the trunk to the outer spread of branches. This figure is squared and multiplied by 3.14 (11). Resulting in the square feet of area to be fertilized.
    The next step is to figure the amount of fertilizer needed, based on the number of square feet to be fertilized.
    The standard recommendation is to use a slow release fertilizer and to apply 2-4 pounds of actual nitrogen per 1000 square feet of area per year. Using a 16- 4-8 analysis slow release fertilizer multiply the weight of the bag (50 Ibs. for example) X .16 (the percentage of nitrogen) which equals to 8 pounds of actual nitrogen.
    Based on the rate of 2 pounds of nitrogen per 1000 square feet, this would enough to treat 4000 square feet. This amount to be applied would to be split into two applications.
    One would be applied in early spring, the second in July (mid-summer). If a 12-4-8 analysis slow-release fertilizer is used, a 50 lb. bag would contain 6 Ibs. of nitrogen. This will treat 3000 square feet. Again, a split application would be used.
    Slow-release fertilizers are recommended because they release nitrogen over an extended  period of time, decreasing the potential loss from leaching, and are less likely to burn the  roots.

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