How to Care for Trees in a Heat Wave

It’s been a long, hot, dry stretch here in Worcester, as elsewhere across the U.S. during this record-breaking heat wave. While it’s nice to have a real summer, the extreme temperatures and lack of rain are placing a lot of stress on our trees, young and old.

The city planted many new street trees this spring. You see them everywhere, waving slender branches, trunks skirted by conical, green plastic water bags. Some look like they are thriving, while others are showing signs of heat stress, their leaves drooping.

Water New Trees Three Times a Week in a Heat Wave
Those green water bags are key to young trees’ survival through this dry, hot period. When filled, the bags slowly release water directly to the trees’ roots, without any run-off or evaporation.

Even under the best of circumstances, new trees need to be watered twice a week, with 5 to 10 gallons each time. When it’s hot and dry, as now, they need a third day of watering, as well.

Mature Trees Need a Good Soaking, Too
Mature trees need water during heat spells, as well. A slow, steady soaking around the base is most effective, using a soaker hose or drip irrigation to conserve water, or a rain barrel with an outlet tap at the bottom. It’s important to soak around the entire base of the tree and to allow the ground to dry out between soakings, so as not to suffocate the roots.

Mulch also helps to retain moisture. It’s best to place two inches of fresh, organic mulch around the base of the tree each spring, after a good ground soaking. Be sure to leave clear the six inches closest the trunk. Ideally, you should mulch the area shaded by the tree, because the root system spreads underground as broadly as the tree’s crown.

We All Need to Care for Our Street Trees
There aren’t enough hours in the day or city forestry staff to water every Worcester street tree on a regular schedule during a heat wave, so it’s important for all of us to care for our trees, young or old, in front of our homes, shading out streets.

Especially if you have a new street tree, monitor the green bag and fill it up twice or three times a week, as needed. In the wake of the Asian Longhorned Beetle infestation, we certainly don’t want to lose any trees from neglect.

Evelyn Herwitz is the author of  Trees at Risk: Reclaiming an Urban Forest and blogs about ALB prevention and tree stewardship at She predicted the 2008 Asian Longhorned Beetle infestation of Worcester, Mass., in her book, published by Chandler House Press in 2001.