Repay trees’ gift of shade with a good long soaking
During this enduring heat wave, that shade tree by the sidewalk is looking mighty good right now.
If you look closely, though, you might be able to tell that the tree isn’t looking so good. It’s much thirstier than you can imagine. If you love trees, this drought with high heat is another terrible thing 2020 has wrought.
Arborists from the public, private and nonprofit worlds are sounding the alarm about what two dry months can do to a tree, even a towering one. They advise us to give all the trees that live near us what they really need — a long, deep drink twice or three times a week until we get a soaking rain.
Yes, drag out the hose, find or carve a groove in the soil so the water doesn’t run off, and turn the water on to a slow drip for several hours. The rule of thumb, according to the Arbor Day Foundation, is 10 gallons for each inch of a tree’s diameter.
“It’s been a strange year to begin with, then that late frost” in May, said Matt Erb, Tree Pittsburgh’s director of urban forestry. “And now the heat wave is putting added stress on plants.”
“We have seen some mortality” already, said Todd Sherbondy, a sales arborist for Davey Tree. “Some had underlying issues going into this, but there are trees in fair to poor health that will never recover.”
The obvious signs of the dry spell are trees whose leaves are wilted, curled, scorched, crispy or discolored.
The last time it rained for more
than a few minutes was May 28, and that was a light rain for a few hours in the night, 0.2 inches, according to hydrologist Alicia Miller at the National Weather Service in Moon. “The last day it rained more than 1 inch was April 26,” she said.
Contrast this summer with the last two, “two of the wettest years we’ve had,” Mr. Erb said, “and what we have is trees that have been babied by all that extra rainfall. Plants will grow roots out further looking for water,” but if they don’t have to do that work, they get lazy, he said. “So these trees have been lazy for a few years.”
That makes them less resilient when the tables turn suddenly, so now they need our help.
City forester Lisa Ceoffe said the city’s many neighborhood partners are putting helpful eyes on trees in distress.
“We are relying on all our tree partners to call in,” she said. “We have been doing some watering at night using big water trucks, and we are riding around looking for trees that are showing distress. Trees along East Liberty Boulevard are showing some stress.
“The mayor’s office is reminding people to water their street trees,” she said.
Even though big trees have a lot of water storage capacity, they need water during this dry spell. About an inch of mulch in a tree pit — but keeping mulch away from the flare at the base — will help keep the soil moist.
Mr. Sherbondy said sensitive trees such as Japanese maples and fruit-bearing trees took a hit during the May cold spell but were bouncing back just in time for the heat wave.
“We can expect to see things get worse as temperatures continue to be high with a lack of rainfall,” he said. “More trees will drop more leaves.”
Trees shed leaves to conserve resources.
“A lot of plants are struggling and losing leaves,” he said. “It doesn’t mean they’re dead, but there are indicators. A shortened branch structure is an indicator of struggle. Undersized leaves.
“If we don’t get rain in a typical week, twice a week of watering would be ideal. If we only get one day of rain a week, I would water a supplemental day.”
He said many trees are well adapted to urban environments, including the London plane tree and pin oak, and some trees do better than others in dry conditions. Some trees go into a drought with pre-existing conditions and jeopardized immune systems, “so you wonder why they are still standing, but they are. Trees as a community step up for each other.”