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Sizzling Summer Stresses Plants, Lawns

Experts say proper watering can save precious landscaping.

As temperatures have “cooled” in during the past couple of days from triple digits to the high 80s and lower 90s, we may all feel a little more comfortable physically.

But what about our flowers, plants, trees and lawns?

Statistics from the National Weather Service (via Chicago Weather Center) show O’Hare Airport has reported that with only 1.18 inches of rain falling from June 1 to July 7 this year, the Chicagoland area has received 28 percent less precipitation than normal.

Coupled with higher than normal temperatures, the lack of rainfall has caused the area to be rated as “abnormally dry” or in a “moderate drought” on an index created by the U.S. Drought Monitor. And with no significant rainfall predicted for the next week or beyond, residents may be wondering what they can do to protect their parched perennials and shriveled shrubs.

“Water,” answers Dan Gombac, director of municipal services for the . 

But before they get out the hoses and sprinklers, Gombac cautions residents to be sure to follow the city’s watering restrictions, which are in place from May 15 through September 15 each year. According to the restrictions, Darien residents may water trees, gardens, lawns, shrubs and other outdoor plants before 11 a.m. and after 7 p.m.

Horticulturists at the Morton Arboretum in Lisle also recommend watering, and, in keeping with Darien’s timetable, the arboretum recommends that residents give their plants and trees a drink early in the morning, before the sun causes the nourishing water to evaporate.

And Richard Hentschel, extension horticulture educator for the University of Illinois Extension Service, worries that the current drought and hot temperatures are putting plants in a stressful state, signaling the need to – you guessed it – water.

What needs water – and how much?

Hentschel said plants manage drought conditions in a variety of ways – from failure to produce fruits or vegetables to loss of foliage. And, he added, plants under stress are more likely to contract diseases and attract damaging insects.

Newly planted trees, shrubs or evergreens need to be watered at the base of the plant toward the edge of the planting hole for at least two growing seasons, Hentschel said. And large, established shade and ornamental trees should be generously watered during extended dry periods, starting several feet from the trunk and extending past the drip line, where roots can absorb the water.

As for lawn care during drought-like conditions, homeowners can choose to keep their grass actively growing though generous watering or allow it to go dormant, Hentschel said. Actively growing means the lawn will need to be watered – and mowed – on a regular basis, keeping the blades green and healthy looking, while in dormancy, the grass will naturally turn a straw color and stop growing, making mowing unnecessary.

In dormancy, the lawn's roots and crown will still need about one-half inch of water per month, Hentschel said. Then, as the weather moderates, the grass will return to an actively growing state, which usually takes about two weeks.

Slow, steady watering is the key to healthy plants

Horticulturists at the Morton Arboretum remind homeowners that trees, shrubs, and other landscape plants absorb water and nutrients through their roots, most of which are in the upper one to two feet of soil, so the goal is to keep plant roots moist, but not wet.

The arboretum offers the following tips for keeping plants and trees healthy during a drought:

  • Depending on air temperatures, trees and shrubs need at least one inch of water applied every week to 10 days to cope with lack of rain. Larger, established trees have a wide-spreading root system and need not be watered as frequently, perhaps every two to three weeks. Let the top few inches of soil dry out between watering to avoid saturation and to allow roots and soil organisms to breathe.
  • Water slowly and deeply so water percolates down into the soil, electing one or two deep waterings as opposed to several light ones.
  • Use soaker hoses and drip irrigation -- effective watering tools because they discharge even streams of slow, trickling water directly to the root zone beneath trees and shrubs. When combined with a three- or four-inch layer of organic mulch, plants can use nearly all of the water that's provided with little evaporation loss.
  • Another effective means of watering a small tree is letting a hose run slowly at its base until the ground is moist. For large trees, let the hose run at various points around the tree's drip line —  the imaginary line on the ground that encircles a tree's extended branches.
  • Water shrubs at the plant base and under the spread of branches until soil is moistened to a depth of six to eight inches.
  • When using a sprinkler system, place a container nearby to measure when you have distributed one inch of water to the soil.
  • Plants vary in their ability to tolerate water stress. Prioritize watering, caring for newly transplanted trees and shrubs first, then those that have been in the ground from two to five years. Next, water "specimen" trees or important trees, then all other plants.
  • Water strategically. Plants absorb more water in the early morning, before the warming sun causes evaporation.
  • Avoid using fertilizer during drought conditions. Fertilizer salts can cause root injury when soil moisture is limited.

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