Daniel Gill, Merrill, Thomas A. | 4/19/2005 10:28:52 PM
By Dan Gill
LSU AgCenter Horticulturist
February is an excellent time to fertilize trees.
Most trees are just beginning to enter a growth phase about now – or they will within a few weeks. Fertilizing this month provides them with nutrients just when they can use them most effectively.
Most of us tend to take the trees in our landscapes for granted. Lavishing attention on our lawns, shrubs and flower beds, we forget that trees are growing, living plants, too, and that they require some of the same care. In particular, the benefits of fertilizing trees often are overlooked.
Trees growing in an urban landscape are more likely to need fertilization than those growing in a more natural habitat.
In the wild, leaves decay in place under the trees that dropped them, recycling the nutrients contained in fallen leaves back to the tree. When we rake up and dispose of fallen leaves to keep our yards neat and lawns healthy, we deprive trees of the nutrients those leaves contain. In addition, urban trees can face lower fertility levels because of top soil removal during initial construction, soil compaction, paved areas and competition from other landscape plants.
Fertilization can be effective in helping trees in a number of ways.
In the first five to 10 years after planting young shade trees can be encouraged to grow more rapidly with annual, moderate fertilization.
Keep in mind, however, that naturally fast-growing trees, such as lacebark elm, swamp red maple, tulip poplar, sycamore and green ash, need less fertilizer to achieve the desired fast growth rate. With these trees, excessive fertilization may even result in an undesirable weaker branch structure.
Also, newly planted trees should be fertilized lightly or not at all in the first year after planting to avoid stimulating excessive vegetative growth before the tree has a chance to establish a strong root system.
On the other hand, proper fertilization helps to maintain the existing growth, health and vigor of mature trees.
Trees provided with proper nutrient levels are better able to deal with adversities such as insect and disease problems or urban stress.
Mature shade trees generally do not need to be fertilized annually. Generally, applications made no more often than every three years are adequate.
When trees are damaged or in decline, fertilization can, along with cultural practices, be an important part of a recovery program.
Trees often are injured by construction or filling that damages their root systems. Physical injury to the upper part of the tree can occur from pruning, lightning, squirrels and lawn maintenance equipment. By increasing a tree's vigor, fertilization can speed healing and help them recover.
If you're not sure if you should fertilize, you can determine the need for fertilization of healthy, mature trees by observing the amount of growth made in spring.
If more than 6 inches of new growth is apparent, fertilization is not needed. If growth is between 2 inches and 6 inches, you should consider fertilizing. And fertilization is recommended if a mature tree has less than 2 inches of new twig growth.
Also look at the foliage of a tree. If it's abnormally small, pale or yellowish, a lack of nutrients could be to blame. Premature fall color and leaf drop in deciduous trees also can indicate a need for fertilization.
Check the pH (soil acidity or alkalinity) and nutrient levels of the soil by having it tested. You can have this done through your parish LSU AgCenter Extension office. The test can determine if there is a problem with pH or a lack of important nutrients. To find out more about soil testing or to locate an office near you, visit www.lsuagcenter.com or check your local phone listings.
Poor color and growth also can occur because of recent transplanting, application of excessive fill, construction, poor drainage, root diseases, insect or disease damage to the foliage, herbicide injury or mechanical damage – particularly to the base of young trees – from lawn mowers and string trimmers. Proper fertilization can help trees recover from some of these problems if the cause also is corrected.
There are many different ways to fertilize trees, and you can use a variety of products. Read the label directions carefully, and follow them precisely when using them to fertilize your trees.
Young trees can be fertilized by simply scattering fertilizer around them. Even larger trees can be fertilized effectively by scattering fertilizer on the soil surface in the root zone. Focus fertilizer applications in a donut-shaped area that centers on the farthest reach of the branches.
Where lawns may be affected by the fertilizer (by the way, trees do get their share of fertilizer you put down for your lawn), it can be placed in holes 1inch across and 8 inches deep, evenly scattered in the root zone of the tree.
Tree fertilizer spikes also can be used to accomplish about the same thing.
If you prefer, you can contact a local tree service to fertilize your tree for you. This might be better for larger, older trees with extensive root systems.
For more information on fertilizing trees, contact your parish LSU AgCenter Extension office.
Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at www.lsuagcenter.com. A wide range of publications and a variety of other resources are available.