Trees depend on soil for a variety of needs, including water, anchorage and nutrients required to thrive.
One of the tools arborists often use to promote soil and tree health is fertilization. Fertilization can assist with providing nutrients that may not be present or are lacking in the soil. Not every tree will benefit from having the surrounding soil fertilized, but most in the urban landscape do.
Nature has worked very hard over the years to develop and refine a cycle for resupplying soils with needed nutrients. Often times, this cycle can be disrupted in the urban landscape through leaf removal, plant selection and lack of a diverse insect population. This is generally the main reason for fertilization.
Sometimes a tree will show signs that there is an issue with a missing nutrient in the soil. Trees with leaves that are a few shades more yellow than they should be can be suffering from one of several different nutrient deficiencies. A certified arborist will know how to spot a tree with this issue and how to narrow down the problem based on the species of tree and local soil conditions.
How do you prepare for fertilization?
Before fertilizing your lawn and trees, it’s a good idea to have a soil analysis done. Most states have offices that provide this service to residents, but a local arborist may offer soil analysis too. Generally, a soil analysis will provide a few basic pieces of information: soil pH, macronutrient content and recommendations for amending the soil. The nutrients most trees require are divided into two categories: macro and micronutrients. Different trees require different amounts of each of the individual elements in each category. Macronutrients are comprised of nitrogen, phosphorous and potassium (NPK), and deficiency in any element can greatly impact a tree’s health and performance.
By knowing the existing levels of the macronutrients, overfertilization can be avoided. Applying excess fertilizer products can be bad for both the tree and the environment, and creates unneeded expense through wasted product.
Sometimes the issues a soil analysis reveals aren’t with the nutrient content, but soil pH. Different macro and micronutrients are more or less available to trees at lower and higher soil pHs. Though it is tricky, changing soil pH usually can be accomplished in a few seasons.
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A certified arborist will understand the reasons for fertilization, how to conduct it responsibly and the science behind the tool. Fertilizer isn’t the answer for every tree, but it’s an important service for an arborist to have in his or her toolbox.
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