Sooner or later, just about any lawn or turf area accumulates excess thatch, that layer of dead stems, roots and runners that builds up on the soil surface.
A thin layer of thatch (up to ½ inch) is usually okay. In fact, it can act as an insulator to keep down soil temperatures, help retain moisture, reduce compaction and help protect the crown of the grass plant.
Once thatch builds up beyond ½ inch, though, it can spell trouble. Excessive thatch can keep water and fertilizer from reaching the soil as it should, and it may create a favorable medium for fungal growth and insect pests. In short, it's not good for healthy turf!
Aeration can help prevent thatch build-up. Some specialists say aeration may be all that's needed for thatch layers up to ¾- or 1-inch thick. Aeration can't remove heavier thatch, though, and that's where dethatchers come in. They come in a variety of designs; all are designed to slice through and pull up accumulated thatch. Some are designed to dethatch and overseed in the same operation, cleaning up existing turf and putting down new seed for a thicker stand.
One of the most popular methods of dethatching is with a vertical mower. Let's look at some of the models available to turf managers.
Different designs for the same purpose
Larger units for golf course and sports-field use are typically towed or tractor-mounted. Jacobsen offers verticut reels for several of their fairway mowers. Bush Hog sells PTO-driven verticut mowers in 3- and 5-gang models that cut up to 138 inches per swath. Ransomes' 214 verticut mower is tractor-mounted with three 30-inch cutting reels.
National Mower offers vertical mowing heads for its 84 Van, 8400 and Hydro Triplex trim mowers. While these units are most often found on golf courses, Stan Kinkead at National says the Hydro 70 especially is a favorite for maintaining high-end sports fields with warm-season grasses. The 8400 triplex units are used for parks, cemeteries and other large turf areas as well. National's vertical-mower blades are shaft-mounted in spiral fashion and have two points per blade instead of the usual five or six points. Kinkead says the mechanical-drive design takes less horsepower to operate than hydraulic-drive systems.
Several companies offer dethatchers for home-lawn use, including rental machines for homeowners who want to do the job themselves. Most machines offer one or more blade options for versatile application in different turf types and varying conditions.
Bluebird's professional model is the P18 Lawn Comber Series, which is available with seeder and bagger options. The seed hopper holds 30 pounds of grass seed. The bagger option attaches behind the unit to collect thatch. The P18 covers an 18-inch swath and is available with a flail-blade reel with 52 free-swinging blades (⅛-inch cutting edge on ⅝-inch spacing) or an optional Delta blade reel with 20 blades on 2-inch spacing. The Delta reel blades feature a 28-degree swept-back cutting angle and beveled cutting edge designed especially for vertical mowing in warm-season grasses.
Bluebird offers a lightweight model, the C18, designed especially for the rental market. The C18 comes with the same reel and blade options as the P18, plus a spring-tine reel option with 52 tines set for ¼-inch operating depth. A folding handle is standard.
Bluebird also offers a tow-behind 38-inch dethatcher that can be hooked to most lawn and garden tractors. The D110 is equipped with a 100-tine spring-tine reel, preset for ¼-inch operating depth.
“Turf managers and lawn-care operators shouldn't hesitate to advocate and promote dethatching services,” says Carla Herron, director of marketing and business development for Bluebird. “Aeration is important for healthy grass and helping control thatch, but aeration doesn't eliminate thatch. Once a lawn has excess thatch, the only way to get it corrected is with a lawn comber or dethatcher.”
Textron offers two units for the lawn and landscape market, both under the Ryan name. The Ryan Ren-O-Thin power rake is available with two reel options, both cutting an 18-inch swath. A flail type reel has ⅛-inch thick blades spaced 1 inch apart. Three fixed blade reels are available:
Ryan's Mataway Overseeder/Dethatcher can be used for dethatching only or combined with overseeding. With an 11-hp engine, the Mataway is designed for major lawn-renovation work. Vertical slicer/dethatcher reels available include a flail blade reel with ⅛-inch wide blades on 1-inch spacing. Fixed-blade reels are available with
Bill Potter, product manager for Textron Golf, Turf & Specialty Products, says dethatching warm-season grasses two or three times a year is not a bad idea. “You can mow grass at normal height and use a fairly thin dethatching blade, not too deep, to cut through some of the runners and stimulate new growth,” Potter says.
“Typically, though, most managers or landscape professionals are lucky to get the job done once. Then, I would recommend a little heavier blade, cut the grass a little shorter before dethatching, and be a little more aggressive.”
Turfco's LS-20 Lawn Overseeder/Dethatcher traces its lineage to the early days of power-rake development. An Illinois company started making power rakes in 1951 and, in 1968, John Kinkead purchased the company and moved the manufacturing operation to Minneapolis. The company later became Turfco, and the LS-20 is now marketed through Turfco Direct, along with the company's other lawn-care products.
The LS-20 is designed for commercial lawn-care use, and as a rental overseeder/dethatcher for professional lawn-care operators. As a dethatcher, the LS-20 covers a 20-inch swath with 28 heavy-duty blades spaced at 1.5 inches. Blades can be set to cut from 1.5 inches above ground level to 1.5 inches deep for use as a “slit seeder.” The seed box holds up to 30 pounds.
Bob Brophy, lawn products manager for Turfco, says the LS-20 can seed “over 30,000 square feet per hour,” whether seeding new ground or overseeding existing turf. “The adjustable depth setting of the blades lets the operator cut a deep enough groove for good seed to soil contact. That results in a better stand of new grass seedlings.”
Tips on timing and operation
Most specialists say cool-season grasses should be dethatched in late summer or early fall — or in early spring. The key is to give the grass some time to recover before winter cold or summer heat sets in.
The best time to dethatch warm-season grasses is early to mid-summer, again with time for plants to recover before seasonal changes slow grass growth. Dethatching is a shock to growing turf, but done at the right time with the right equipment, grass will recover and fill in relatively quickly.
For lawns with bare spots or poor condition, overseed along with dethatching. Make sure blades cut grooves deep enough for good seed-to-soil contact. Some professionals suggest raking grass after overseeding, then applying a light mulch or top dressing and raking again. Water as for new grass.
If you don't overseed but are concerned about weeds filling in before the grass does, apply a pre-emergent after dethatching.
For heavier turf such as bermudagrass or zoysiagrass, a vertical mower is almost a necessity. For fescue or bluegrass lawns, a light dethatching can be accomplished with a wire-tine unit. A more aggressive dethatching job where thatch is heavy will require cutting blades.
Don't replace aeration with dethatching. The two go hand-in-hand for good turf maintenance. Aerate once or twice a year to maintain healthy turf. Power rake as necessary to open up grass and get rid of excessive thatch layers.
Gary Burchfield is a freelance writer specializing in equipement topics, based in Lincoln, Neb.
50 YEARS OF DEVELOPMENT
Dethatchers got their start on the golf course. Superintendents needed a machine to cut through and pull up thatch, especially with warm-season grasses that put out excessive runners when heavily fertilized and intensively maintained. Turf managers liked the look and quickly adopted the dethatching idea for home and commercial lawns.
Tom Fiske, general manager of Kinco Manufacturing in St. Paul, Minn., says the original power rake concept was started in 1951 by the Henderson Company in Fisher, Ill. “As far as I know, that was the first design. John Kinkead bought that line in 1968 and moved it to Minnesota and began improving on the power rake design. We experimented with different blade combinations, straight or offset, fixed or flail type. Landscapers really liked the units because they were light and easy to maneuver and haul around.”
Kinkead, now retired, also founded Turfco Manufacturing in Minneapolis, and Fiske says manufacture and marketing of the Kinco power rakes were turned over to Turfco in the early 1990s. Turfco further developed the line and still offers the LS-20 Lawn Overseeder, a combination dethatcher and overseeder, to lawn-care firms today.
Vern Worrell remembers working on power rake development with the Ryan Company (now part of Textron) in St. Paul. “When I went to work for Ryan in 1969, it was a small company with about 70 employees, and we were building sod cutters. Management was looking to add other turf equipment, so we began working on a power rake.”
Worrell says the engineers determined that blade shape was important for removing thatch without excessive turf damage. Speed and rotation of the dethatching reel were researched as well. “We soon discovered that dirt and sand caused rapid wear of the dethatching blades, so we experimented with several types of steel, different steel-hardening processes, even coating the blade cutting edges to make a hardened surface.”
He says blades tended to last longer on golf greens than on regular turf because of the greens' more uniform soil structure. “We also discovered that greens needed to be dethatched at least once a month or power raking wasn't very effective.” They ended up reducing blade spacing to about ½ inch instead of the 1-inch spacing they had been using.
“You had to be more careful doing the dethatching, though, or it would tear up the green too much. We eventually came to the conclusion that core aerification is a better way to control thatch on golf greens. You can go deeper with the coring tines and take out more of the soil profile/thatch layer.”
Worrell says, however, for home lawns, sports fields and regular turf areas, power raking or vertical mowing is still a viable dethatching option. “It depends on what you need to do. A spring-tine power rake will pull up lots of dead grass and clippings to open up the turf. But thatch layers are mostly below the soil line and that takes a blade-type dethatcher to cut through the matted layer.”
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