Summer Mowing Heights: To Raise Or To Lower?

Do you raise the mowing height during summer, causing grass to slow down its growth cycle and provide shade for the roots and soil? Or, do you lower the height to stunt its growth and let it brown out naturally when irrigation is not an option? Opinions vary on the proper practices, but correct mowing heights depend on the variety of grass, the area of the country and, especially, the contractor doing the work.

RAISE THE HEIGHT. In Memphis, Tenn., Jerry Rochelle, maintenance department division manager for Michael Hatcher & Associates (www.memphislandscaper.com), maintains properties with zoysiagrass, Bermudagrass and a variety of fescues. Typically in the summertime, Rochelle will raise mowing heights to reduce heat stress. He said, "If we can’t keep enough water on the grass, we stress out really bad. So we try to get the height up and let the roots get some relief."

The majority of the company’s properties have zoysiagrass, which Rochelle typically keeps at about 2.5 inches high in spring and early summer. He then bumps the height up to about 3 or 3.25 inches during the summer stress period. That increase occurs as the summer heat peaks in Memphis, which Rochelle expects to happen in early July this year as it did last year. That is about half a month earlier than typical Tennessee summers, but he plans to adjust accordingly to protect his properties.

For Bermudagrass, Rochelle keeps it at about 2.5 inches most of the year and increases the height to 3 inches or, at the most, 3.5 inches during summer. Rochelle mows the fescues at 3 to 3.5 inches most of the year, and increases them slightly to 4 inches in the summer. Approaching fall, he slowly works all of the varieties back down to the typical springtime heights through the fall and winter dormant seasons.

The Ohio State University extension, department of horticulture and crop science agrees with raising mowing heights in the summer. The department says to raise cool-season varieties, such as Kentucky bluegrass and perennial ryegrass, as well as fine fescues, from their typical spring and fall heights of 2 to 2.5 inches up to 2.5 to 3 inches during summer stress. For tall fescue, the department suggests keeping its height at the normal 2.5- to 3-inch range.

Turfgrass Producers International (www.turfgrasssod.org) Executive Director Doug Fender also concurs with raising mowing heights during summer stress. His reasoning is not only to protect the turf, but also to conserve water. The organization is developing a program named Water Right, which is intended to educate people on proper turf watering practices such that instead of watering bans, people would have the right to water their lawns as long as they water them right. Part of proper watering practices is related to the height of grass.

For both warm- and cool-season grasses, Fender suggests raising the mowing height such that it peaks with peak temperatures. "You should then maintain it at that height during the peak temperatures – which could last 2-3 months – and then you can start bringing them back down again," he said.

Fender explained that the increased amount of leaf blade on taller grass, although it will transpire more water, acts as a coolant for the grass and soil. Cutting grass lower reduces the amount of evaporative loss, but also reduces the ability of the plant to cool itself and to shade the roots and soil. "It helps the plant maintain itself at a cooler temperature so it doesn’t reach that critical or fatal temperature as fast as it would with a shorter blade," he explained.

LOWER THE HEIGHT. Lowering the height of grass in the summer goes against most of the literature and studies one can find about mowing turf. It is also a different practice than what the above sources follow. However, at least two companies actually lower mowing heights during summer stress periods and have healthy turf to prove that the practice works.

One of those companies is Roswell, Ga.-based Ed Castro Landscape Inc., an irrigation, maintenance, lawn care, design/build and erosion control provider. Scott Foster, the company’s landscape manager in its maintenance division, said he lowers the mowing heights of warm-season grasses, such as Bermudagrass, zoysiagrass and centepedegrass, in the summertime compared to fall. For the first spring mowing around late February and early March, the company typically scalps these varieties of turf as low as possible to about 0.5 inches to remove old thatch and dried clippings. Then Foster lets the grass get to a springtime height of 2 to 2.5 inches.

As summer rolls around, Foster then cuts the grass back to between 1 and 1.5 inches until fall. "The more you cut it low, generally, the more you going to make it thicken up," he explained. "Actually, letting the grasses get stressed a little will make them grow the roots deeper. It will stimulate them to look for water and grow down looking for it. You don’t want to let the lawn dry up, but if you wait until it shows signs that it needs water, you’re better off than just automatically watering it."

For the fall and into winter, Foster said he lets the warm-season varieties get a little taller to avoid potential winter kill from a hard freeze. "When it starts to go into dormancy, if you let it get a little bit higher, it will go into the winter better," he said. Conversely, Foster raises the mowing height of fescue varieties from 3 inches in spring to about 4 inches during summer stress periods. Then in the fall, he low cuts the fescues to about 1 to 1.5 inches before aerating and overseeding to give the seed a chance to germinate before the grass grows and shades out the seed.

Hilton, N.Y.-based R.M. Landscape Industries Inc. services mostly unirrigated properties consisting of Kentucky bluegrass mixed with perennial rye and some fescue varieties, according to Todd Meyer, salesman and designer. Therefore, crews for the maintenance, erosion control and design/build company usually mow those properties every other week. Although Meyer said the company has not had any major stress situations on its properties this season due to a large amount of rainfall, the company has in the past intentionally cut the grass low to put it into a stress situation so it stops growing completely. "That happens when the grass has already browned out some," he explained. "So we let it brown out completely by cutting it short. We do this because we have no way of bringing it back to healthy on an unirrigated property."

A customer may wonder if the company has destroyed his lawn by letting it brown. However, Meyer said, "We’ve never had a problem with the grass not coming back." By letting the grass brown out and stay short, the company’s mowing schedule on such properties can sometimes increase to every three weeks. Although Meyer was unsure of the exact mowing heights the company uses, he did know that the first few cuts in spring are about 3.5 to 4 inches because the grass is growing so rapidly. As the summer approaches, the company gradually steps the height down and then raises it again by fall.

OTHER PRACTICES. Besides changing mowing heights in the summer, the above contractors also cite other ways to help grass make it through the summer stress period.

Rochelle from Michael Hatcher & Associates has used Primo plant growth regulator to thicken the turf while stunting its growth. He has used this product effectively on zoysiagrass and has been able to increase the time between mowings up to two or three weeks following use of the product. "I’ve still got the look for the turf, and I’ve still got the stability," he said. "I’ve just stunted its growth."

Foster from Ed Castro Landscape looks to proper watering practices to keep turf healthy. "We’re watering deeply rather than frequent shallow waterings," he said. "By giving them one really good watering as opposed to two light waterings, you get the roots growing deep." In the Atlanta area, he tries to give properties a deep watering twice a week and sometimes three days a week depending on the temperatures. That practice may become less of a possibility if the Georgia government bans watering due to the state’s current drought watch. If that happens, Foster is not too worried about losing his customers’ lawns. "Generally plants are going to recover a lot better from being too dry than from being too wet," he said.

Whether raising or lowering mowing heights, the key to success is to plan ahead because grass takes time to adjust to changes in care. Fender from Turfgrass Producers International said, "Grass is relatively slow to respond. You’re not going to get deeper roots in a week just because you want them." He says the key is to look at historical data and recent weather trends to determine the typical weather patterns in an area. As far as making future determinations based on the weather today, Fender said, "Looking at the same season is always going to put you behind the eight-ball." He suggests placing more stock in the historical data. This will help in deciding when to start raising or lowering the deck to reach the desired grass height when the summer stress period is in full swing.