After shivering and sloshing through a cold, wet spring, that might be hard to imagine — but it’s time to think about watering the garden.
“Trees and other plants in the Midwest go through a kind of mini-drought every July and August,” said Sharon Yiesla, a plant science specialist at Morton Arboretum in Lisle. “That’s only a few months away, so homeowners should start preparing now.”
By thinking ahead, you can help your plants avoid water stress, which can weaken them and make them more susceptible to pests and diseases. The mass of a mature tree is about 35 percent water, and a tomato plant is at least 90 percent water.
“All types of plants need adequate water to stay healthy throughout the summer,” Yiesla said. By July, they have long since used up the water that the rains in April and May brought to the ground.
But if we’re not careful, it’s also easy to overwater. “Not only is it wasteful, it’s harmful,” Yiesla said. “Too much water can affect plant growth and lead to some types of diseases and pest problems.”
For example, overwatered lawns provide a perfect habitat for grubs, many of which hatch into Japanese beetles.
Here are some suggestions from Yiesla to prepare for this summer’s watering.
“Watering on a set schedule is a recipe for over- or under-watering,” Yiesla said. “If the system kicks in when there is already moisture in the soil, it encourages maggots and root rot. Turning it on briefly two to three times a week will barely wet the soil surface. This keeps the grass and other plants submerged while the water bill still goes up.”
Instead, turn off the timer. Only turn on the sprinklers manually to water deep once you have determined that the soil is actually dry.
“We have to be more careful these days because our climate has changed and made the weather more volatile and unpredictable,” she said. “We can’t make assumptions from 20 or 30 years ago.”
Many gardeners have a habit of watering every morning or Saturday. Instead, make a habit of checking the soil to see if it needs watering or not. The easiest way is to dig a few inches deep with a trowel, touch the soil to see if it’s moist, and look at the plants growing in the spot.
“For lettuce seedlings, you need moisture in the top inches of soil, but for established trees, shrubs, perennials, and lawns, as little as 2 inches of moisture in the soil is sufficient,” Yiesla said.
Your goal should be to moisten the top 6 inches of soil. Then allow enough time—more time in cool weather, less time in hot weather—for the water to seep deeper and the top few inches of soil to dry out. Water again after checking the soil for moisture.
When these hoses are laid on the ground in garden beds, their tiny perforation allows water to slowly seep out their entire length. Soak hoses deliver water directly into the soil where the roots are.
“They reduce the risk of plant diseases because they don’t wet the foliage,” Yiesla said.
Because the water seeps in so gradually, the roots have time to absorb it. Drip lines are less wasteful than sprinklers because they don’t throw water through the air that is lost through evaporation. Establish hoses early, then cover them with mulch and leave them in place throughout the season.
Since their root systems are not yet mature, trees and shrubs need additional watering for the first two to three years. You can water them with a drip hose, a sprinkler, special watering bags tied around a tree trunk, or even a bucket.
“Water deep, right near the base of the trunk where the roots are,” Yiesla said. “As a rough rule of thumb, plan on taking 10 to 15 gallons every week or 10 days, depending on the weather.”
Among many other benefits, a layer of mulch prevents water from evaporating from the soil. In perennial beds, an even layer 1 to 2 inches deep will do. Around trees and shrubs, spread mulch evenly over a wide area about 3 to 4 inches deep. “Just be careful not to mulch the trunk,” Yiesla said.
For tree and plant advice, contact the Plant Clinic at Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or firstname.lastname@example.org). Beth Botts is a staff writer at the Arboretum.