Caring for Your Trees During a Drought
Caring for Your Trees During (or Before) a Drought
Hint: They need Water
Although fall rains have provided relief to the severe drought conditions that plagued our area this summer, technically our region is still listed as experiencing mild drought and who knows what next year will bring. Some of our trees have suffered from lack of water and may continue to show lingering effects into next year. The best time to protect your trees against a drought is before it gets severe. While the immediate danger may be behind us, knowing what to do in case extremely dry conditions return in 2023 may help you ward off further damage to your trees. Watering trees adequately, checking them for pests and disease, and consulting a certified arborist if you suspect a problem may increase the likelihood that your trees can survive future drought conditions.
How Drought Affects Trees.
In the short run, drought interrupts the cycle by which water moves through the tree from the roots to the leaves. First the finer hair-like roots, typically located close to the surface, die back. Eventually larger roots can die back as well. While roots can grow back, this process takes time. Drought weakened trees are more susceptible to threats from insects and disease, the effects of which may show up months or even years after the drought. For a more detailed description of how drought affects trees please see this article from UMASS Amherst.
Which Trees Need Help?
While some trees are better able to tolerate drought than others (many oaks, pines, eastern arborvitae, sweetgum to name a few), any tree can suffer from lack of water, and all trees, regardless of drought tolerance at maturity, need supplemental watering in the first years after planting while they are establishing their root structure.
Trees with wilting, yellow, curling, or marginally scorched leaves, early leaf drop or bark cracks, crown dieback, or thinning foliage as well as signs of insect damage need some attention during a drought.
What Should I Do to Help My Trees?
Newly Planted Trees
You should plan on watering newly planted trees for one year per caliper inch of diameter unless they are receiving adequate rainfall on a weekly basis, even if we are not technically in a drought situation. The root systems of newly planted trees are damaged during the planting process and need time and water to regenerate for the long-term health of the tree. During a drought it is critical to water newly planted trees.
To determine if you need to provide supplemental water to your mature trees first simply observe them. If you notice signs of stress, it may be time to water. Next, know your soil in depth. Surface dryness or moisture doesn’t tell the whole story. Dig a whole 6”-12” deep and see if the soil is cool and moist. If it’s dry you will need to water and then make sure that you are watering deeply enough so that water is penetrating the soil.
Watering and Other Care Tips:
Water Slowly and Deeply
You want to deliver water slowly so that it has time to penetrate the soil. This encourages a deeper root structure and may enhance drought tolerance. Drip lines or soaker hoses deliver water slowly and help reduce evaporation. Mulching over a drip line can reduce evaporation even further. Slow-release watering bags can also be used for newly planted smaller trees. New trees may need more frequent watering than mature trees. A good starting point for mature trees is 1” of water once a week. Check your soil to ensure that this is adequate and adjust the length of watering time if needed. Deep watering is better than frequent surface irrigation.
Photos by Anne Benning, L- example of a tree watering bag, R- Drought stressed maple with watering bag
You want to deliver water over the entire zone under the tree’s canopy. Tree roots extend at least this far out from the trunk. Try not to water the trunk itself. Watering widely encourages root growth and promotes resiliency. Soaker hoses or drip lines work well to cover the entire area under the canopy
photo by Anne Benning: Soaker Hose with Mulch
Eliminate the Competition
Grass or other ground cover beneath trees will compete for any water delivered to your tree. Consider removing it and replacing it with mulch, which will help preserve soil moisture. Do not apply mulch against the trunk itself. If you leave the ground cover, you will need to increase the amount of water provided to the tree.
Continue to check soil moisture around mature trees. It’s tempting to stop watering after a big rainstorm, but dry conditions may persist especially if the water has not penetrated the soil to an adequate depth. You may need to water well into the fall.
Watch also for signs that your trees are suffering longer term or secondary effects from the drought. Thinning leaves, dead branches in the canopy, signs of insects or disease may appear after the drought has ended. Consulting a certified arborist may be help save a mature tree.
If you plan on planting new trees in the future, consider planting native species that are more drought resistant. Give them a good start with a surface irrigation system of some sort, adequate mulch, and careful attention for their first three or so years. A list of Water Wise trees can be found here