The Mysteries of Fertilizing Trees

Do My Trees Need Fertilization?

Trees in urban settings are subject to many stressors that are unknown in their natural environments: insufficient or excessive irrigation, planters too small for a healthy root system, repeated wounding by landscaping tools like lawnmowers and weed wackers, and nutrient-deficient soil. These and other stressors make trees more susceptible to pests and disease that can cause defoliation or even partial or total failure.

Signs of Soil Deficiency

Do not apply fertilizer to trees without an arborist’s recommendation. Doing so can cause harm if the tree doesn’t need fertilizer or if the wrong kind of fertilizer if applied. However, here are a few signs that may signal that a tree or group of trees need fertilization:

  • pale or yellowing leaves
  • mottled leaves
  • defoliation
  • stunted twig or tree growth

When Should I Fertilize?

If your arborist agrees that your trees need fertilization, the best time to apply it is during the cooler months. Start scheduling fertilization treatments now (in late summer) in order to get the healthiest, greenest trees next year.

Natural Trees in Unnatural Settings

In nature, trees grow where they are best suited according to the amount of sun, rain, and wind the area receives, as well as by the makeup of the soil. Each tree receives needed nutrients as its own fallen leaves decompose and feed its roots, and roots are able to breathe because shade and fallen leaves prevent grass from growing over them. It’s a perfect system that is impossible to reproduce for trees planted next to buildings, beside concrete paths, and (worst of all) in parking lots.

Fertilization is one way to compensate for poor soil, but it is not a cure-all.

Fertilizer Can’t Do It All

While proper fertilization can make up for a lack of needed nutrients in soil, it won’t overcome some of the environmental factors discussed above and it should never be given to trees suffering from drought or fugal infection.

Consult your arborist to find out whether fertilization is the right treatment for your trees and get on a fertilization schedule so that your tree population remains strong, healthy, and resistant to the many stresses of urban life.