Trees Will Let You Know When They Need Fertilizer

When it comes to fertilizing trees in your landscape, the trees themselves will often tell when and how often they need a little fertilizer. Of course the only sure-fire way to know is to have your soil tested, which we can help you with at the Extension office.

Without a soil test, the best indicator of the need for additional fertilization in established trees is shoot growth. If new shoot growth- that occurring in the present year - is more than six inches, the tree probably doesn't need fertilizer. If shoot growth is less than two inches, fertilization should help.

Foliage color is another indicator of a lack of nutrients. Yellow or 'off-color' leaves may indicate the need for fertilization. But remember that 'off-color' leaves are normal or certain plants, in particular, some maple and ash trees in the fall.

A final indicator of the need for fertilization is landscape history. Trees in established lawns that are fertilized on a regular basis rarely need supplemental fertilizer. Consider supplemental fertilizer only if shoot growth is less than two inches per year, or if a soil test shows a specific
nutrient deficiency, such as boron, zinc or magnesium.

If the only indicator is slow shoot growth, then apply a high-nitrogen fertilizer to the tree, such as 16-4-8 or 18-24-12. But if the leaves are yellowing or there are other indicators of nutrient deficiency, then its probably a good idea to have the soil analyzed.

Most trees have a single flush of growth during spring, followed by slower growth throughout the summer and fall. It's desirable to have nutrient available to the tree as this flush of growth is about to occur.

The best time to apply fertilizer is mid-March and again about the first of May. If you are fertilizing just to maintain tree health, use a balanced fertilizer such as 8-8-8 or 10-10-10.

Fertilization is particularly important for flowering trees, such as the crape myrtle. To encourage more prolific blooming, fertilize crape myrtles in late May with about a cup of 10-10-10 per tree.

For more specific information on fertilizing and caring for your trees, access the UGA Forestry publication, Tree Nutrition Series: Nitrogen Prescriptions for Trees, at
www.forestry.uga.edu/warnell/service/library/index.php3?docID=283

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