Cool gardening tips for a hot summer yard
July 14, 2011
  • /Crop Sciences
Heat, humidity, storms, bugs, weeds and mosquitoes all add to the drama in yards and gardens during the hot summer months, said University of Illinois Extension horticulture educator Ron Wolford. He shared a few tips for coping.


Lawns need about 1 to 1 1/2 inches of water per week to maintain their green color, so first decide whether or not to let your lawn go dormant during hot, dry summer weather.

"Do not let the lawn go dormant and then start watering it again to green it up," he said. "This practice uses large amounts of the grass's food reserves. Water lawns early in the day and avoid watering between 10 a.m. and 3 p.m. This is the hottest part of the day, and you will lose 50 percent of the water you apply. Watering in the evening will increase the chances of disease problems. If watering with a sprinkler, place coffee cans in the area to measure water application rates."

During the summer when grass growth slows, mow the lawn at the 3-inch height. Lawns mowed at a higher height during the summer will have fewer weed problems and deeper roots.

"Mowing too close just invites weeds," Wolford noted. "Don't mow the grass when it is wet and never remove more than one-third of the grass leaf in any one cutting. If you mow your lawn on a regular basis, you do not need to collect the clippings. Clippings are 75 to 80 percent water and will decompose down into the lawn. Clippings have some nitrogen content, so less fertilizer is necessary."

Late summer is the best time to repair lawns. Seeding bare spots in the lawn during this time period will allow the new growth to have enough time to germinate, grow and harden off before cold temperatures arrive. There is less competition from weeds in the fall because a lot of the annual weeds die out. And the cooler temperatures in the fall are great for growing grass.

Ideally, dig the soil to at least 6 to 8 inches deep, spread grass seed over the area and tamp down. Keep the soil moist until germination. Cover with weed-free straw to conserve moisture. If you are laying down sod, water the new sod several times a day for one to two weeks until it begins to knit or take hold. Be sure that water goes down through the thick sod and moistens the soil underneath for good root development. Do not let sod dry out.


"Reduce favorable breeding sites for mosquitoes that cause West Nile virus," he said. "Keep your gutters free of debris because clogged roof gutters make great breeding sites. Clean and freshen water in pet dishes, wading pools and birdbaths. Cut back tall weeds and grass because they can be hiding places for mosquitoes during the day."

For more information, go to the University of Illinois Extension web site: Preventing West Nile Virus (

Watch for the emerald ash borer. The adult borer is a 1/3- to 1/2-half inch-long emerald green bullet-shaped beetle.

"Look for the adult beetle on leaves and trunks of ash trees," he said. "Look for 1/8-inch wide D-shaped emergence holes in the bark of ash trees. Female beetles will lay eggs and after the eggs hatch, larvae will bore through the bark into the cambium.

"The larvae will feed, making winding tunnels under the bark, disabling the tree's ability to take up food and water. Initial symptoms will include dieback at the top of the tree. The tree will usually die within two to three years."

For more information, go to the University of Illinois Extension web site, Emerald Ash Borer Central at (

Watch for yellowjackets in August. Yellowjackets are ½-inch long, yellow and black-banded wasps. Yellowjackets are attracted to open cans of pop, open garbage cans, perfumes and bright clothing. Keep garbage and pop covered with lids. Keep rotting fruit under trees cleaned up and avoid wearing brightly colored clothes. Above all, do not try to swat yellowjackets away with your hands and arms. Be aware that a yellowjacket can sting repeatedly. They will only sting if they are disturbed.

"Check your roses and other ornamentals for Japanese beetles," he said. "Adults are copper colored with shiny metallic green heads. They will skeletonize leaves during the day from 9 a.m. to 3 p.m. The beetles may be active well into August. Control them by picking the beetles off by hand. Japanese beetle traps may attract more beetles than they control."

Trees and Shrubs

Apply a 2- to 4-inch layer of organic mulch around trees and shrubs. Mulch the area under the tree to its drip line. The drip line is the circle that could be drawn on the soil around a tree directly under the tips of its outermost branches. Keep the mulch 4 to 6 inches away from the base of the tree or shrub to prevent rot. Organic mulches will reduce weeds and conserve moisture. As the mulch decomposes, it can be dug into the soil, thereby adding nutrients to the soil and improving soil structure.

Water trees and shrubs during hot, dry periods. It is especially important to water trees planted this growing season. Established trees will also need water if conditions remain dry. Water the entire root zone. The root zone area extends beyond the drip line or outermost branches of the tree.

Avoid overwatering trees, especially those growing in clay soils. Trees have died because of roots sitting in very wet soils.

Edible plants

"Watch for blossom-end rot on tomatoes," said Wolford. "The blossom ends of tomatoes turn brown to black. Peppers and summer squash can also have this problem. This is not a disease. The condition results from a calcium deficiency caused by wide fluctuations in soil moisture. Maintain even levels of soil moisture to control blossom-end rot. Applying mulch around tomato plants will help."

During hot weather, pick your tomatoes every couple days. Temperatures of 90 degrees F and higher can speed up the softening process, slow down color development and reduce quality. Picking your ripening tomatoes will also keep the squirrels from snacking on them.


Powdery mildew is a very common problem, especially during wet summers and at the end of the growing season. Powdery mildew leaves white spots on leaves, shoots, buds and stems. It really doesn't harm the plant, but it doesn't look good.

"To avoid mildew, space plants properly for good air circulation," he said. "Try to avoid wetting the foliage when watering because that can help to spread the disease. Buy varieties of plants that are resistant to mildew."