You’ve watered the lawn, the flowers, and the shrubs and saplings, but have you watered that big tree that provides shade for those pampered parts of your yard?
If not, trouble may be brewing.
“Oftentimes people wait too long before they come to us,” said Sara Wallace, a plant diagnostician with Oklahoma State University Cooperative Extension.
“A man yesterday said, ‘They have a little green left on them. Can they be saved?’ Well, no, but when it was the reverse, a little bit of brown and a lot of green, we could have helped.”
Wallace said lately the lab staff at OSU is diagnosing a lot of Hypoxylon disease, which damages tissues in the inner bark and sapwood used by the tree to move water from the soil to the leaves. The fungus that causes the problem is ever-present in trees, especially oaks, but competing fungi usually keep it in check.
“It happens when the tree is stressed,” she said. “If it was an outside pathogen, maybe you could cut off a part of a tree and save it, but when it’s systemic, and the tree is mostly gone, there isn’t much you can do.”
“I talked to a guy yesterday who has six dead oaks and thought it was oak wilt, but we don’t have that in this state. I’m guessing it’s Hypoxylon. We’ve had a lot of that coming to the lab lately.”
She said the sad part is that it’s preventable, and trees can recover when early signs, like browning leaves, are noticed.
During the hot, dry months, the best simple maintenance is deep watering and taking some soil tests to check the ph and soil health. For smaller trees, a layer of mulch can help retain soil moisture. People can turn in soil samples at county extension offices, and a $10 fee is all it takes to get a detailed report in a week or two. The report shows the soil pH and recommends actions to take. Information on the process is available online at https://extension.okstate. edu/. Wallace said that deep watering is more than just the typical watering of a lawn or flowerbed for a few minutes each morning.
Sometimes people with lawns on an auto-mated sprinkler system and a beautiful green lawn don’t understand how their big shade trees could possibly be stressed, she said.
“Turf can get 15 minutes a day in the morning on an irrigation schedule, but, especially if there is turf under the tree, the turf just sucks all that up,” she said.
Most people are careful with saplings and smaller trees as they grow, but only some give much thought to watering trees once they mature, she said.
Deep watering means getting water to the tree’s roots, which typically involves soaking the ground thoroughly with a trickle from a hose, even if it’s just once or twice a month.
Wallace said that people often envision trees as having deep tap roots, but most of a tree’s root system spreads horizontally away from the trunk and is 6 to 24 inches deep.
She said the area around the tree, away from the trunk, is where to do the watering. Wallace described the critical area as “what would be in the shade if the sun was directly overhead.”
“Leave the hose on at a slow pace, half-pressure or quarter-pressure, for 30 minutes or an hour and then move it to another spot,” she said.
Younger trees need more water more frequently, she said. Soil type makes a difference as well. Trees in sandy soil will need water more often than those in clay soils.
The needs apply to both evergreens and deciduous trees–and the rules apply year-round, in winter drought, summer drought, and summer’s extreme heat, she said.
The Oklahoma Ecology Project is a nonprofit dedicated to in-depth reporting on Oklahoma’s conservation and environmental issues. Learn more at okecology. org.
