Ask a Consulting Arborist Q&A: Tree Care Tips (Pruning, Water, and More)

Q: How to save a drought-stricken tree

Thursday, July 07, 2016  

Q: We live in central Washington State, and the last several summers have been hot and dry. We have two emerald green Norway maples in our front yard that are approximately 80 years old, but they haven't been watered for several years. We built a house here three years ago, and last year we put in a lawn sprinkler system. The water system comes on for a couple of minutes several times a day, but we don't do any deep watering. The building crew was careful when they put in the sprinkler lines. One of the trees seems to be doing fine, but the top died in the other one last year. This year when it leafed out, the leaves were smaller and lighter green than the other tree. But now in June, some of the lower limbs have leaves turning yellow. Is there anything we can do to save this tree?

A: Norway maples are reasonably drought tolerant but have their limits. New construction and last year's drought severely stressed a lot of trees. Construction raises the soil and air temperatures around trees and causes tiny roots, the thickness of our hair, to dry and die—and these are the roots that absorb the majority of water and nutrients trees need.

Lawn irrigation doesn't get deep enough to benefit the trees, and lawn fertilizers can harm tree roots—especially for stressed trees.

Recommendations:

  • Proper Watering:
    • Can you provide deep watering for most of the dripline/root zone?
    • Deep means slowly getting the water to penetrate 20 to 24 inches into the soil.
      • Drip hoses are a good way.  Dig a hole after a few hours and see how far the water is penetrating
    • If you can get the trees watered deeply once a month from now until the end of October, they will likely respond.
  • Mulching:
    • If you can remove some of the lawn and put down 2–3 inches of mulch, such as arborist chips, it will help tremendously.
      • Most arborists will deliver chips for little or no charge.
    • The larger the area of mulch under the tree, the better.  A circle around the trunk is the idea.
  • Feeding:
    • A quality tree service in your area should be able to inject a tree-based fertilizer, that is, a fertilizer specifically formulated to meet the chemical needs of the tree, into the soil. This can be a big help. They inject this in a water mix into the soil below the roots of the lawn.
    • Beneficial microbes:
      • You could try a mix of beneficial bacteria and fungi.
      • These are naturally occurring microbes that benefit the tree by increasing absorption of water and nutrients, protect against pathogenic attack, and help with drought tolerance.
      • They can be put in the tank mix with the fertilizer and injected at the same time.  Do this right away.
  • Trimming:
    • It is good to have a professional prune the deadwood.
    • It must be done with clean climbing techniques—no climbing spurs!
    • Only prune the dead wood.  Do not allow anyone to “thin” or “wind sail” your trees.  Right now they need all the photosynthetic capacity they can muster to recover from the stresses of construction and drought.  They need all the solar panels (leaves) to produce as much photosynthates as possible.

 

Responder: Brian Gilles, RCA #418, Kirkland, WA