A heat wave challenges a lawn on two fronts. When the mercury rises above 90°F, the turf’s food production is slowed significantly. A lawn struggles to create enough essential carbohydrates during a heat wave. At the same time, the high temperatures cause excessive water loss from the leaves. Soon stress builds within the lawn and damage begins to show up. To limit heat stress and help your grass maximize its available resources, follow these 9 expert tips during a heat wave.
- <strong>Dr. Kevin Frank</strong> is a professor and turf exension specialist at Michigan State University.
- <strong>Dr. Aaron Patton</strong> is the executive director of the Midwest Regional Turf Foundation and a professor of horticulture at Purdue University.
- <strong>Aaron Steil</strong> is the statewide consumer horticulture specialist at Iowa State University.
1. Mow High
Move the mower deck up to a cutting height of 3.5 or 4 inches for cool-season grasses, such as Kentucky bluegrass. Most warm-season grasses can be cut at 2.5 inches or so during a heat wave.
Mowing high provides for the greatest amount of leaf area possible so plants can harvest light for photosynthesis, explains Dr. Kevin Frank, a turf specialist at Michigan State University. Cut the grass low and you’ll instantly reduce the plant’s ability to generate energy, plus the plant will throw all its resources toward producing new leaf tissue.
2. Mow During Coolest Time of Day
During an afternoon of high heat, turf grass wilts to preserve leaf moisture. If you put heavy equipment, such as a lawn mower, on wilted grass or grass nearing the point of wilting, it can damage leaf blades. The damaged leaf tissue often dies, creating tracks of dead turf across a lawn from the mower wheels. Frank recommends mowing in the early morning or late evening to reduce the risk of damaging turf.
3. Sharpen Mower Blades
Dull blades create a ragged leaf edge, which is the ideal entry point for diseases. Heat-stressed grass has limited energy to combat disease. A small infection can grow quickly in high heat. Keep mower blades sharp.
It is common for mower blades to begin to dull after weeks of spring and early summer mowing. Sharpen them mid-season, even if a heat wave is not in sight, to avoid issues later.
4. Water Smart
The amount of water your lawn needs to stay green during high heat depends on the type of grass, soil makeup, and sun exposure. At least 1 inch of water a week is recommended to keep a cool-season lawn green. If a green lawn isn’t critical, “with far less water you can keep your lawn alive,” says Aaron Patton, turf specialist at Purdue University. “Water once every 2 to 4 weeks with a half inch of water to keep turf plant crowns hydrated during drought,” he says. The grass will go dormant and the leaf blades will turn brown, but the crown and roots will remain alive, and the lawn will green up 1 to 2 weeks after significant rain.
Warm-season grasses use water more efficiently and don’t require as much irrigation to remain healthy during high heat. Provide about a half-inch of water a week, adjusting the amount as needed based on the health of the turf.
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5. Water in the Morning
If you need to water your lawn, do so between 5 and 9 a.m. According to Aaron Steil, extension specialist at Iowa State University, that’s when you’ll lose the least water to evaporation. Plus, watering early in the day gives the turf grass time to fully hydrate before the heat of the day sets in. Well-hydrated turf can survive heat stress much better than wilted turf.
6. Water Deeply
When watering the lawn, apply the weekly recommended amount in a single application or 2 applications 3 or 4 days apart. This helps encourage grass roots to grow deeper into the soil, which boosts its drought-tolerance. If you water more frequently and and apply less than the recommended amount each time, you’ll encourage shallow rooting and lush growth, which will struggle more in heat and drought. Plus, this will make your lawn more susceptible to pests and diseases.
7. Don’t Fertilize
Fertilizer spurs grass to grow quickly and growth demands carbohydrates which are in short supply during a heat wave. Wait to fertilize until after the heat wave passes. Generally, cool-season grasses are best fertilized in fall, and warm-season grasses are fertilized in early summer.
8. Give New Lawns Extra TLC
New seed or sod demands even more attention during a heat wave. Twice-daily irrigation is essential for newly laid sod during a heat wave. Water in the early morning and again in the early evening, delivering enough water so that the sod and soil remain moist and cool. Sod should be firmly rooted in 10 to 14 days after it is laid. After it is rooted into the native soil, water the sod deeply and less frequently.
Care for new seed in a similar way, keeping the seed bed moist but not saturated until the turf is about 3 inches tall. When possible, avoid establishing a new lawn in the heat of summer.
9. Wait on Weed Control
High heat causes many types of weeds to flourish while turf grass languishes. It might be tempting to apply an herbicide to tame the onslaught of weeds, but don’t waste time and money. High heat significantly limits the effectiveness of herbicide. As always, time your herbicide application for the type of weeds you are aiming to control. For example, crabgrass treatments are most effective when applied in spring, and fall is ideal for controlling broadleaf weeds.
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