The drought is likely coming for your garden. You may notice it first when lawn grass turns brown, but other plants are in the line of fire. “Drought can do long-term damage to trees, shrubs and other plants,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. “They all need your help to get enough water to survive this.”
Most of Northern Illinois is in moderate or severe drought, according to the U.S. Drought Monitor website. At the Arboretum, only about half as much rain was recorded this spring as in the drought year of 2012. In fact, it was the driest spring since 1936 — a year when nationwide drought created the Dust Bowl in the Great Plains.
Although early July brought 2 to 3 inches of rain to some parts of the Chicago region, it was not enough to end the drought and plants are still under threat.
“Understanding how drought affects each kind of plant can help you make good choices about where to put your watering efforts,” Yiesla said. Here’s what you should know.
Lawns: Without regular watering, lawn grasses will go dormant. The grass blades die back, becoming brown and dry, but the roots will usually survive. “This is a normal process,” Yiesla said. “In the wild, grasses go dormant every year in the dry months of summer. We keep turf grass abnormally green in our lawns by watering.”
To conserve water in a drought year, let the lawn do what comes naturally and go dormant. Give it just about 1/2 inch of water every 2 to 3 weeks — enough to keep the root system alive without causing the lawn to stay green. If the drought becomes even more severe and the grassroots die, it will be easier to replace a lawn than to replace other plants such as trees and shrubs.
Trees: Drought damage can affect trees for years to come. “We saw trees dying six or seven years later from the effects of the 2012 drought,” Yiesla said. It’s hard to see the impact at first because the damage is happening underground: As soil dries out, the fine feeder roots that collect all water for the tree begin to die. If a tree loses much of its root system, it will no longer be able to absorb enough water even when the rain returns. A shortage of water flowing from the roots up to the leaves and stems will affect every life process of the tree.
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“Trees need water in summer to form their leaf and flower buds for next year,” she said. “Drought-stressed trees may have fewer leaves and flowers next year.” Trees will struggle to form fruit later in the summer, and they will also be more vulnerable to pests and diseases.
Since mature trees improve property values and provide shade, make watering them a priority. “To keep the feeder roots alive, concentrate on watering out to the drip line — in other words, water the ground area covered by the tree’s branches,” Yiesla said. Pay particular attention to watering newly planted trees.
Water trees and all plants thoroughly, so that water soaks down 5 to 6 inches into the soil. That will encourage feeder roots to grow longer and deeper, increasing the plant’s water-holding capacity. Mulch can help by preventing water from evaporating from the soil surface. Water well, and then spread a 3-to-4-inch-deep mulch layer over a wide area around the tree. The mulched area should extend at least 3 feet from the trunk. “The more root area you can cover, the better,” Yiesla said.
One drought effect in trees is highly visible. “They are likely to change color early, and let their leaves dry out and fall,” she said. “They go dormant early to try and save themselves from the drought.”
Shrubs: Although some shrubs, such as yews, are generally tough enough to survive most droughts, others, such as hydrangeas, have shallow roots and are vulnerable. Flowering shrubs that are stressed by drought this summer will struggle to bloom next spring. Make sure all your shrubs’ roots are covered with a layer of mulch and water them regularly. Prioritize plants installed in the last two years.
Perennials: Even plants labeled as “drought tolerant” will need some watering. Some plants may have brown, scorched leaves, and some may die. Native prairie plants are often described as drought tolerant, but that’s only after they have matured and grown a large enough root system to store water. Those planted within the last couple of years will still need watering. If the drought continues all summer, even prairie plants may be stunted, with few flowers.
Vegetables: Many vegetable plants, such as tomatoes and peppers, evolved in rainy, subtropical regions and need their soil to be steadily and evenly moist. “Make sure your beds are mulched to keep in water,” Yiesla said. “Check the soil often and water enough to keep it moist in the top 6 inches.” Plants will draw more water from the soil as they grow larger.
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.