Saving Your Trees in a Time of Drought

by Birgitt Evans, Master Gardener and ABG Board Member

watering trees in drought

Trees are the largest living organisms in the landscape and the most important. Trees take carbon out of the atmosphere and store it in their roots and tissues, they cool the ground and reduce the heat island effect, they slow, sink and spread rainwater to prevent runoff and recharge aquifers and they can provide fruit or sweet blooms. They also take the longest time to grow and replace. And so, when we are asked to reduce water to our landscapes, it is critical that our trees are first in line for our landscape water.

This past winter our soil contained moisture from December through the beginning of April, rather than from October through May as it normally does and so many trees are probably experiencing drought stress. Symptoms of drought stress in trees are:

  • Leaves that wilt or droop and do not recover by evening.
  • Yellowing or browning of leaves and leaf drop beyond what is normal for the tree. (Redwoods drop leaves in August, so look at whether the drop is excessive compared with previous years.)
  • Fruit drop in fruit trees and a failure to produce blossoms in flowering trees.
  • A lack of new growth or new growth that is stunted.

And if you removed a lawn or mulched over part of your yard, the trees are no longer getting water from that soil, causing them even more distress. Tree roots are fairly shallow, running 12 – 28 inches below the soil surface and will spread out long distances in search of water. To keep your trees alive and healthy through a drought:

  • Apply a 4 to 6 inch layer of wood chip mulch (not bark which will not break down and add to the soil) starting 8″ from the trunk and extending out past the furthest reaches of the branches, which is called the “drip zone”.
  • Use a moisture meter or trowel to check water levels 6 – 8 inches deep all around the drip zone of the tree. If it is dry, you need to water.
  • Water mature trees slowly and deeply along the entire circumference of the drip zone once a month, using a hose on low or oscillating sprinkler. Remember that soil that has already been allowed to dry out is hydrophobic and will not easily absorb water. If the water starts to run off, turn off or move the water, wait until it is absorbed and then water the area again until the water begins to run off. This could take awhile in really dry soil. If you test your soil again and it is still dry you may have to dig holes to water into, or otherwise manually manipulate water and soil until the soil absorbs the moisture. Water needs to reach the roots so it needs to go down two feet into the soil.
  • For young or newly planted trees, create a watering basin with a berm around it and water slowly inside the basin.
  • Install a soaker hose or drip system starting with concentric rings of hose starting a foot from the trunk and spaced a foot apart out to the drip zone. Water for 30 minutes and then wait an hour and water for 30 minutes. Repeat this until the water has seeped down two feet. (Use a trowel to check.)
  • Install a simple Laundry-to-Landscape greywater system to water your trees. No permit is required. Check out Greywater Action for detailed instructions.
  • Never fertilize a drought stressed tree since that increases its need for water and could kill it.
  • Do not heavily prune a tree during a drought as this will promote new growth and increase the tree’s need for water.
  • Remember that your street trees need water too.

As the West gets drier and we face more droughts, properly caring for our trees will become more and more important so that they can remain beautiful and healthy and continue to provide all the benefits for which we rely on them.

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