Water helps dried tree leaves recover from dry spring, cold weather

Are you seeing brown, dry leaves on trees this spring? They may have been damaged by cold weather.

“We didn’t get a hard freeze this spring, but we have had nights that got cold enough for frost,” said Sharon Yiesla, plant knowledge specialist at The Morton Arboretum in Lisle. Several times in April, it was cold enough to damage new leaves that had just opened from their buds.

“The good news is that the trees can recover,” Yiesla said. “Just be patient, and the trees will develop new leaves to replace the dried-up ones.”

Frost damage is especially obvious on young trees, but it also can be seen on older trees, such as the ginkgos in The Grand Garden at the Arboretum. It may affect some or all of the tree’s leaves.

If you see brown leaves all over an oak tree all through the winter, though, you probably aren’t seeing frost damage. Those are last year’s leaves, which normally cling to an oak’s branches until new leaves open in spring.

New leaves are the ones vulnerable to frost damage. “It happens if cold hits just when the leaves are new and tender,” Yiesla said. Although there were spells of 80-degree days in April and May, there also were nights below the 32-degree freezing mark.

When the water in plant cells freezes, ice crystals slice the cell walls so water drains out. Without water in the cells, the leaves dry up and die. Freezing is a special danger for new leaves because they are thin and flimsy, with little protection against the cold.

To help your tree recover, make sure it has enough water. “A plant needs water to build new leaves,” Yiesla said. “In spring, when leaves are unfurling all over the place, plants use up a lot of the water that is in the ground.” Grass around trees also competes with the tree’s roots for water.

Rain helps, but rainfall has been short in much of the Chicago region. According to the Illinois State Climatologist, most of northeastern Illinois received only a half to a quarter of normal rainfall during April and May. “In a dry spring, it’s a good idea to water a frost-damaged tree, or any tree,” Yiesla said.

The best way to water a tree is slowly and deeply, with a barely trickling hose or sprinkler. For a recently planted tree, make sure to place the water source right on the root ball, near the trunk. Older trees will have extended their roots farther, so you will need to move the hose around a few times.

The time and amount of water needed will depend on the particular conditions in your yard, but as a general guideline, trees planted within the last two years need 10 to 15 gallons of water every 10 days or so.

“The easiest way to tell whether a tree, or any plant, needs watering is to check for moisture in the soil,” Yiesla said. Regardless of how much it has rained, what matters to a plant is whether the soil actually contains water for its roots to absorb.

With a trowel, dig down about 2 inches near the tree, and touch the soil to see if it feels nicely moist. If not, water.

For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.