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Saturday, June 15, 2013

Removing Thatch from Bermudagrass and Poa Invasion

Q. I cant get my bermudagrass to look good, like the golf courses do. I think one of my problems has be mowing too low, believing it would still green up if I did that. I dont overseed it for a winter lawn. I just let it turn brown. Over the last two weeks I've raised the height and fertilized. 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 wider leafs, presumably poa.  Probably little I can do to stop the poa.

A. Depending on the bermudagrass it could be mowed up to one inch tall. However most bermudagrass would like to be at about 1/2 inch in height. Lower than this is for the professionals in my opinion and requires very frequent mowing to look good. The lower you mow, the more often  you have to mow to look good. 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.
Poa will leave dark green spots when it invades bermudagrass like it has in the right side of this picture. It grows more
upright than bermuda, soft and usually a darker green unless the bermuda is young and succulent.

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.
This is a poa seedhead or inflorescence. Poa seeds heavily and can be seen
as a discoloration or graininess to the poa.

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. 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.

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