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Thursday, June 6, 2013

Bermudagrass Lawn Requires Dethatching to Look Good

Q. I cant get my bermudagrass lawn to look good. I would like it to look more like a golf course grass. I think one of my problems has be mowing too low, believing it would still green up if I did this. Over the last two weeks I've raised the height of my cut and fertilized. It is looking much better but probably need another week for it all to get up to the same height. I'm getting small patches of darker green grass with a wider leaf. I think this is what they call Poa. Probably little I can do to stop this Poa weed.

Poa annua or Poa as the turfgrass professionals like to call it (or annual bluegrass as some call it) in dormant bermudagrass in December
A. Depending on the kind of bermudagrass it could be mowed up to one inch in height. However, most bermudagrasses perform very well cut at about 1/2 inch in height. Lower than this is for the professionals, in my opinion, and requires very frequent mowing, a grass catcher and fertilizing frequently to look good.
Mowing should be done so that you remove no more than 1/4 to 1/3 of the leaf blade. If
you mow when the grass is too long, like in this picture, you leave behind clumps of grass
clippings. I like to call this hay mowing, not cutting the lawn. This also means that when you mow
your lawn short it will reach this 1/4 to 1/3 threshold that much faster and you must mow very
often. Golf Course Superintendents have some bragging rights when they mow their greens and
tees at 3/16ths. Can you imagine mowing to remove only 1/4 to 1/3 of the leaf blade? This means
mowing daily or in some cases twice a day! Homeowners should not be mowing less than 1/2 inch on
bermudagrass unless you want it to own you!

            The lower you cut the grass, the more often it needs to be mowed. When you have a thatch problem, mowing low will make it look worse. You really have to address the thatch problem this fall. If you don't overseed, the best time to do it would be in late summer (August) so that the grass has time to mend before winter sets in. After dethatching, fertilize and water heavily to speed up the repair process.
Thatch comes from dying roots, rhizomes and stolons of bermudagrass. Once it starts to accumulate, then clippings from mowing will also contribute. This must be removed in heavy thatch producers like most bermudagrasses.

            There are fewer weed problems when the grass is opened up from dethatching in the fall than the spring. When you open up a lawn in the spring there are lots of spring weeds that can invade. Yes, the small dark green patches with seedheads on many of them now is Poa. Poa is tough to control. The seed is everywhere and tracks with shoes. If your bermudagrass is an improved type you can green it up more with nitrogen and iron and this way the Poa is not as noticeable. But it will always grow a bit faster and is wider bladed than the fine bladed improved bermudagrasses. Poa is a cool season grass so if you don't overseed the Bermuda you could spray it out in December or January with Roundup when the Bermuda is dormant. The problem will be the Poa seed that is everywhere in your lawn. It WILL come back.
Dethatchers or vertical mowers (the blades spin vertically rather than horizontally as they do in rotary mowers) or even sometimes called verticutters lift the thatch debris from lawns where it can be gathered together for compost. Dethatch in the fall months when weed invasiont after dethatching is less than in the spring months.

I was just looking again at your response to my email. One benefit of overseeding is that it helps to eliminate some of the thatch because you must dethatch the lawn sufficiently for the seed used in overseeding can make good contact with the soil for germination.

May years ago common bermudagrass would be burned in the winter to get rid of the dead surface grass and in the process any thatch accumulation. It is still recommended that bermudagrass hayfields be burned for numerous reasons including thatch removal and reduction of insects and diseases. Years ago bermudagrass lawns were also burned in the rural areas. We didn't have a thatch problem when bermudagrass was burned in the winter. Because we cannot burn dead grass any more due to local ordinances, this dead grass remains and adds to the thatch layer.
Its a proven fact. Mowing affects the rooting depth of grasses. Close mowing
results in shallow rooted lawns. Shallow rooted grasses are more
prone to drought problems than lawns mowed higher

We now substitute a gasoline-driven machine (called a dethatcher, vertical mower or verticutter) instead of burning the dead grass. This of course uses petroleum, adds pollutants to the air and leaves this bermudagrass thatch that we have harvested for dumping somewhere.

A  tool I have used in the past is the Red Dragon propane torch to burn debris. The model with higher BTU's will burn grass even if it is wet. This is an advantage because you can wet down the bermudagrass dead lawn and still burn it which makes it more safe to use. There are lots of advantages to burning bermudagrass thatch but local ordinances may prevent you from using it. The burning is done just before spring growth.