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Question of the Week © 2017 Mike McGrath

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Grass Wars: Bermuda vs Fescue in Virginia

Q. Is there any sure way to kill the Bermuda grass that has taken over about 70 percent of my tall fescue lawn?

---Dennis in Vienna, Virginia

A. Of course it can be killed! But then you'd have less than one-third of a lawn left. Not a good plan. Now—the devil is always in the details, so we asked Dennis the basic 'cultural questions' whose answers could explain such a takeover: who cuts the lawn; how high is it after cutting; who feeds the lawn; and with what?

Dennis responds: "I cut the lawn myself and keep it around three or four inches tall."

Okay—that's close to perfect. Cool-season grasses like fescue thrive with a three-inch cut, while scalping lower than that would favor intrusion by a warm-season grass like Bermuda, which can tolerate a much shorter cutting height. No help there.

Dennis continues: "For fertilizing and weed control, I use a service that applies {"Gulp!"} six feedings a year" (!). Yikes!

OK—ding. ding, ding! Six feedings a year is four feedings too many. Cool-season grasses like Dennis' dearly-departed fescue do best with two feedings a season; a light 'meal' in the Spring, and a bigger feeding in the late summer/early Fall. The Spring feeding gets the grass ready for the stress of summer to come and the 'Fall' feeding helps the grass recover from that summer stress. Feed a cool-season grass like fescue in the heat of summer and it will burn up, especially if that 'food' is the 'conventional' high-powered, salt-based chemical nitrogen.

And; you know; come to think of it, that many feedings has to be illegal in Virginia…

Yes; illegal. Several years ago, both Maryland and Virginia enacted legally binding restrictions on the amount of fertilizer that can be applied to a lawn and the timing of those applications. Basically, fertilizers can only deliver around nine pounds of nitrogen per thousand square feet, can only be applied twice a year, and can't be applied between November and March, when the grass wouldn't be able to utilize it and all of the fertilizer would wash into the Bay.

These laws are designed specifically to protect the Chesapeake Bay. That's why they also prohibit the use of any phosphorus unless a soil test shows that it's absolutely necessary. Phosphorus is the fertilizer most devastating to waterways.

Now: Do people obey the laws? Probably not. Heck, many homeowners don't even know about them. But they should know and obey—because following the guidelines these laws establish will both protect the Bay and deliver a much better-looking lawn.

Overfeeding grass is as bad as overfeeding people and pets. In the case of turfgrass, overfeeding leads to massive build-ups of thatch, as well as increased pest and disease problems. And again, if you feed a cool-season lawn like bluegrass or fescue in the summer, it'll severely stress the grass—and fuel the growth of warm-season grasses like Bermuda and warm-season weeds like crabgrass.

So: what can Dennis do now?

Bermuda IS a widely-used (by choice) perennial lawn grass. It's also a very aggressive spreading grass. So if Dennis does nothing (often my favorite option when gardening choices must be made), it'll take over the remaining 30 percent of his lawn by August of next year. Then Dennis will have a one-grass lawn that's relatively easy care, as Bermuda loves DC-area summers and grows sideways to fill in its own bare spots.

(Oh, and because it is a warm-season grass, that care will be very different. Dennis should reduce the cutting height a bit and only feed in the late Spring and mid-summer. You don't feed warm season grasses like Bermuda in the Fall.)

And if he instead wants his fescue back? A lot of work lies ahead. Any herbicide that can kill Bermuda would also prevent any success with new grass, so Dennis will need to have the old turf removed with a big, noisy, and highly effective machine called a sod cutter. If he does this in the Spring, he could then install a turf-type tall fescue sod right away. Sod is more expensive than seed, but you get an instant lawn.

If he's going to sow a new fescue lawn by seed he would remove the old turf in July and August, have a truckload of compost spread over the bare surface and then spread the new fescue seed between mid-August and mid-September.

And how do we prevent the return of the Bermuda?

Eternal vigilance and proper lawn care. Fescue is a great grass—it grows slowly, handles lots of foot traffic and doesn't require as much food or water as bluegrass. But, as we have been stressing, it can't spread to fill in the inevitable bare spots, and you must overseed it every few years in mid-August to mid-September—so be sure you can get matching seed!

Start with a branded seed or sod that has a specific variety name, and use that exact same 'named' seed when you make your repairs. Otherwise, you could wind up with a patchwork quilt instead of a unified turf.


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