2005 Year in Review

Drought Causes Stress on Garden, Landscape Plants

Hot, dry weather affects plants differently. Plants wilt, trees and shrubs show symptoms of leaf scorch, and lawns go dormant.

“Wilt occurs when water loss from the leaves is greater than uptake by roots,” explains David Robson, University of Illinois Extension horticulture educator. “Even with adequate soil moisture, leaves may wilt during the hot part of the day. Hydrangeas are a good example. But, when the sun goes down and temperatures cool, they usually recover. On the other hand, wilting plants in pots or barrels probably do need a good watering.”

It’s easy to diagnose wilting in flowers and many vegetables. Leaves collapse, droop and don’t appear turgid or stiff. Blossoms fade and die soon after opening.

Tomatoes and corn exhibit symptoms seldom seen in other vegetables. Tomato leaves roll under while corn leaves roll up. Unfortunately, once tomato leaves roll, they seldom straighten out with additional moisture. Corn can recover if water is applied soon after.

Robson says garden crops may abort flowers if the weather is too hot and dry. Tomatoes, eggplants, peppers, squashes, melons and pumpkins are notorious for this condition.

Established trees and shrubs are less likely to show wilt symptoms. Instead, they exhibit “scorch” characteristics. Scorch shows up as browning of leaf margins and the tissue between the veins. Leaves feel crisp or leathery. The contrast between the normal green color and brown of scorch is obvious. Scorch usually starts along the margins and progressively gets worse as the plant continues to suffer. If the soil is extremely dry, entire leaves and branches may die. Certain trees and shrubs are willing to sacrifice entire limbs to reduce the stress on the entire plant. Lower and older limbs usually die before younger ones. Smaller branches are forfeited before larger ones.

Most lawns tend to go dormant and turn brown when water is at a premium. Robson says dormancy is an ideal stage for cool-season grasses such as bluegrass, fescue and ryegrass to survive summer’s conditions. However, green lawns can wilt. The walking test is the best indicator.

If footprints remain in the grass 15 to 30 minutes after walking, the lawn is wilting and should be deeply watered. Avoid mowing the lawn in this state as the added stress can kill plants and thin the turf.

As a rule of thumb, most plants need 1 inch of water per week during the active growing season. When temperatures climb above 90 degrees, plants may need at least 2 inches of water each week.

Water early in the morning to decrease the chance of diseases and lessen evaporation. Irrigate slowly so the water percolates into the soil instead of running off. Also, water where the roots are located. The entire flower or vegetable garden may not need to be watered if the roots haven’t spread all over the garden. A tree’s water-absorbing roots are at the drip-line of the plant, not congregated around the trunk.

Robson also says mulch can limit water loss from the soil. Apply 2 to 4 inches of wood chips, straw or other mulching material to garden and landscape plants.

For more information about helping garden and landscape plants endure the dry weather, request the Dealing with the Drought fact sheets from the Whiteside County University of Illinois Extension Office, 815/772-4075, or download them at U of I Extension. .

by  Editor, theCity1.com
July 11, 2005