Rx for landscape woes: Water trees and shrubs, not lawn

The combination of record-setting temperatures, an intense heat wave in early July and less than half the normal rainfall in some areas scorched many Northeast landscapes this summer. So, according to Cornell scientists, what's your best bet to save your grass, trees and shrubs?

Water your trees and shrubs, but not the lawn.

"Overwatering during hot weather does far more damage to a lawn than drought," said Frank Rossi, turf specialist in Cornell's Department of Horticulture. Watering -- particularly frequent, light watering -- encourages lawn diseases and weeds, he explained.

The cool-season lawn grasses commonly grown in the region naturally slow down as temperatures rise and soil moisture decreases, even in normal summers, noted Rossi. In hot, dry years like this, he suggests just letting the lawn go completely dormant. In most cases, they'll green up again in late summer or early fall when the rain returns and temperatures moderate.

But that's not the case with trees and shrubs, said Nina Bassuk, director of the Urban Horticulture Institute. "When it's really hot and dry, many trees and shrubs will shed their leaves -- and some will just dry up. Drought is very stressful and can sometimes kill them outright," she said.

Newly planted trees and shrubs are particularly vulnerable because their root systems aren't fully developed. Depending on the species and site, that might mean keeping two- to five-year-old plantings carefully watered during dry periods to prevent drought-caused leaf damage or loss.

But don't give up on trees and shrubs that have shed their leaves, says Bassuk. "Go ahead and water them," she suggested. "It's better late than never. If they're still alive, they'll grow new leaves."

The key to watering trees and shrubs is to water them slowly and allow the water to soak deep into the soil with no runoff. One solution is to use plastic drip irrigation bags that encircle the trunk of the tree. They can be quickly filled with a hose and slowly release the water (typically 20 gallons) over 8 to 12 hours. Special soaker hoses can also deliver water at a slow rate.

If you have a few trees and shrubs to water, you can use a hose turned on to a slow trickle. Another low-tech solution is to drill small holes in the bottom of plastic buckets or trash cans, place them around the trees and shrubs, and fill them with water.

See the Cornell Horticulture blog for watering tips for trees, shrubs and lawns.

Craig Cramer is a communications specialist in the Department of Horticulture.

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