Fertilizing and Use of Herbicides and Pesticides We recommend caution when you consider fertilizing trees or using chemical herbicides or pesticides around the base of a tree. The more we alter conditions by using chemicals, the more vulnerable a tree is to damage from overuse or misuse of chemical compounds. When injury results in a tree due to fertilizer burn, it is usually difficult to correct. If an established tree is in the right native soil, most likely it already has access to the nutrients it needs to flourish. Mulching is the safest and most economical way to fertilize a tree. Nitrogen fertilizer should be applied only if an arborist or soil test indicates that it’s needed. Fertilizer not absorbed into soil can pollute the environment; overdosing can harm or kill your tree. Using fertilizer during hot weather can also severely damage your tree.
Occasionally, if you have hired an arborist or a Maryland LTE to evaluate a tree, they might recommend fertilizing an older tree that is showing signs of distress. Our bottom line: Use a soil test kit and test before fertilizing or consult an expert before applying fertilizer to tree roots. Trees growing in the right soil typically will not need to be fertilized. If an expert recommends fertilizing one of your trees, or if you have used a soil test kit to find the correct mix for fertilizing a specific tree and want to do the project yourself, we offer the following guidance.
Always test soil before applying fertilizer. Otherwise, you can create an imbalance in soil composition that can upset the health of a tree.
Based on the results of the soil test, head to your local home improvement store to buy the fertilizer. Tree fertilizer is not the same as fertilizer for grass. Look for “Deciduous Tree” or “Evergreen” and water insoluble nitrogen (WIN) on the label. You should use a slow-release fertilizer to protect the quality of water in our watersheds. Always follow the directions on the label of the fertilizer. vii How to Apply Fertilizer to Your Trees viii ● Before fertilizing, use the information from soil testing to determine what nutrients are needed, how much to apply and when. ● Choose one of the following three methods of application: o Fertilizer stakes: Push fertilizer stakes into the ground below the roots of the grass. You will need gloves and a mallet to hammer the stakes about 10 inches into the ground. o Granular fertilizer: Dig or drill 10-inch-deep holes into the soil. Anything that can be used to plant flower bulbs will work well to dig the holes. Some home and garden stores rent or sell small augers. Place the granular fertilizer into the holes. o Liquid fertilizer: Inject liquid fertilizer 8-10 inches below the surface into the soil with a probe. This is the preferred method of the pros, but unrealistic for most homeowners without the special tools.
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