In the Heat, Plants May Need Extra Water

While you sip ice water to refresh yourself from the triple-digit heat, The Morton Arboretum recommends you also "refresh" your trees and shrubs to prevent them from becoming stressed or weakened. Their survival may depend upon the care you provide now.

Container plants, newly-planted trees and other plants, and drought-susceptible species are most at risk during these sweltering temperatures, says Doris Taylor, Arboretum plant information specialist.

"These high temperatures are like a double-edged sword," Taylor says, explaining that scorching temperatures make plants transpire (exhale moisture) more quickly, and therefore use the soil moisture more rapidly than on cooler days. Also, moisture is evaporating straight out of the soil more quickly, she says.

Drought-sensitive trees and plants likely showing the effects of blistering temperatures may include magnolias, Japanese maples, dogwoods, beeches, larches, tulip trees, and birches. Also, hydrangeas are likely suffering a bit because they're shallow-rooted and therefore drought-sensitive.

Taylor has seen "leaf scorch" - a browning of the leaf edges - on several trees, including katsura trees, which are also drought-sensitive.

Container plants can dry out and wilt fairly easily; they should be watered quite a bit, Taylor says. If plants are in full sun, they likely require more water.

Newly-planted trees, shrubs and perennials are still establishing their root systems and should receive one-inch of water weekly.

To check the soil's moisture, either use a soil probe or place your finger in the soil. If it is dry and hard, watering is appropriate. If there is some moisture, continue to monitor the soil's moisture level. Containers in full sun likely need watering more frequently than containers in shade, which can retain water more easily.

The Arboretum recommends watering within the dripline of a tree, from the trunk out to the end of the branches, to reach the roots most effectively. The objective is to keep roots moist but not wet. Constantly saturated conditions can also damage roots.

So-called "Gator Bags" - plastic, water-filled vessels that envelope a tree trunk - provide a slow drip to the root system and are a good way to keep your tree well watered.

Remember to keep two to four inches organic mulch layered around a tree to moderate soil temperature and retain moisture.

Taylor reminds us to keep trees and plants healthy throughout the year.

"We went through a major drought last year, from which some plants are already weakened, Taylor says. "Weakened plants are more susceptible to pests and diseases." 

Grasses are not so much at risk from the hot, dry conditions at this time, because they require minimal amounts of water to keep them actively growing, she says.

The Morton Arboretum is an internationally recognized 1,700-acre outdoor museum with collections of more than 3,700 kinds of trees, shrubs, and other plants from around the world. The Arboretum's natural landscapes, gardens, research and education programs, and year-round family activities support its mission - the planting and conservation of trees and other plants for a greener, healthier, and more beautiful world.

Visit www.mortonarb.org or call 630/968-0074 to learn more.