It is important to take good care of trees, including fertilization, because they provide shade, oxygen, beauty, and depending on the variety, fruits and nuts as well. The recommended method of tree fertilization is deep root fertilization. This involves using some method to penetrate the soil to a depth of around three to four inches, and not more than eight inches (or deeper, depending on the type of tree) in order to feed fertilizer down to the root level. The small feeder roots lie near the surface of the ground. A well-fertilized tree will live longer and be able to better withstand disease and insect invasion. It will also be more beautiful in appearance.
Tree Fertilizer Components
Like all living things, trees need many nutrients to thrive. Some of these are nitrogen, phosphorus, calcium, magnesium, sulfur, and potassium, and others. A soil test kit will help you determine which, if any, nutrients your soil is lacking. Then you can fertilize accordingly. If your trees are planted in the lawn, the fibrous grass roots are competing with the tree roots for nutrients from the soil. In this case, deep root fertilization would be indicated.
Ideally, the type of fertilizer purchased will be a versatile one that will allow some of the nutrients to release quickly, but others to release more slowly so as to be absorbed by the tree roots as they are needed.
The Need To Fertilize Trees
Trees that grow in town or in residential areas are often highly stressed due to lack of moisture, damage sustained, disease, insect invasion, soil compaction, nearby construction, or competition from grass and/or other vegetation growing close by. Even poor air quality in large cities can affect the tree’s health. Newly planted trees should be fertilized, and then fertilized again every 3–5 years. A soil test kit is available from your county Extension office and will tell you what nutrients the soil needs in which your tree is planted.
Trees growing in urban areas often are not able to draw the necessary nutrients from the soil because there is too much competition from other grass, trees, and vegetation. A tree should be fertilized right after being trimmed to speed the process of the cut places healing over.
Another reason trees growing in yards, parks, or urban areas need to be fertilized is that in our quest for the perfect yard, we rake the fallen leaves in the autumn and dispose of them. But if they were left on the ground to decompose naturally, they would provide all the necessary nutrients that trees need.
Visible Signs Tree Needs Fertilization
Without using a test kit, there are other ways to determine whether or not your trees need to be fertilized. Check the new shoots growing on the tree. If they grow six inches or more in a year, that tree probably doesn’t need fertilizing. If the growth is between two and six inches, some fertilization is indicated. Growth of less than two inches will make fertilization mandatory for optimum tree health. Foliage color is another indicator of whether or not the tree needs to be fertilized. Yellow or “off-color” leaves may indicate a lack of nutrients in the soil. This test probably won’t apply in the autumn when leaves are changing color anyway.
A third thing to consider is where the tree is planted. If it is in a lawn that gets regular fertilization, the tree is probably all right, too, unless a soil test indicates otherwise. One other sign of lack of fertilizer is the tree leaves becoming smaller and smaller each year. This indicates that the tree is literally starved for nutrients. Tree diseases, insects, and dying or broken limbs are other indicators that the tree is seriously lacking in nutrients.
Time Of Year
Trees should be fertilized either in the spring, preferably in March or April, or in the fall, in October or November. Fertilizing in the fall allows the soil to soak up the nutrients and be ready to be absorbed when the roots awaken in the spring. Roots continue growing and feeding long after the leaves have fallen, even into the winter months, as late as December. They awaken and begin the cycle again as early as April.
Fertilizing Methods For Trees
Merely scattering the fertilizer on the ground around the tree won’t do. The fertilizer will burn the grass and leave brown spots in some cases. It is necessary to inject the fertilizer below the surface, down close to the roots, so as to help the tree without harming the grass. Often a small-diameter tube with an injector needle is used to accomplish this process. A shovel can also be used by the do-it-yourselfer. Just insert the shovel to the desired depth and push it forward far enough to open the soil and put in the fertilizer.
However, a professional arborist will use special equipment that includes a tank containing the fertilizer, a hose, and an injector that is capable of injecting the fertilizer to the required depth. This not only applies the fertilizer to the tree roots, it also aerates the soil to allow much-needed oxygen in where the roots are.
The area to be fertilized should be both just inside and just outside of the canopy circle, known as the drip line. The arborist will make several injections around the canopy circle, to ensure that the fertilizer gets to all the root areas.
Forest Trees vs. Landscape Trees
A person might think that trees don’t need to be fertilized, based on what one sees out in the country or in the woods. No one goes out into the woods with fertilizer, so how do those trees stay healthy? They receive their nutrients from the fallen leaves and decaying plant matter that cover the ground. In town or in our yards, we clean up the fallen leaves and other plant debris, and thereby deprive the tree of its natural fertilizer.
If you need the services of a certified arborist to come and deep root fertilize your trees, just give us a call.
http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/tree-fertilization-guide/