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Pennywort, Dollar Weed and Other Woes of Wetness

Q. My gardens and lawn are being taken over by pennywort. How can I get rid of it? Our yard has a lot of toads, lizards, tree frogs, butterflies, and hummingbirds, so I don't want to use anything toxic. I have tried to control it with Roundup, but nothing kills this stuff! Help!

----Mary in Beaufort, North Carolina

A. Well unfortunately, that Roundup may have been the most toxic option for this specific situation. Research by Dr. Rick Relyea of the University of Pittsburg has shown Roundup to be deadly to amphibians, like those frogs and toads.

But it's no surprise that our listener has both a yard full of amphibians and "pennywort" (a plant that's perhaps better known as dollarweed.) A Clemson University Extension Service Bulletin describes it "as a water-loving plant that can float" and explains that it's mere presence "indicates excessive moisture in the area." Heck--the prefix of its scientific name is even 'Hydro'!

Now, most people know that too much water can kill plants, but many are surprised to hear that wetness can actually encourage a weed. In fact, those two points can combine to create the worst-case scenario in these situations; the extreme moisture levels that encourage plants like dollarweed are also going to weaken just about every desirable plant in the area, especially lawn grasses.

Now, let's be clear—reducing the moisture will not get rid of this weed completely. Nothing can. Millie Davenport, the Clemson Extension Agent who wrote the Bulletin, wisely states that complete eradication is essentially impossible, even with toxic herbicides. The achievable goal, she notes, is to knock it back to a tolerable level.

And better drainage is absolutely the first step in that direction. Research performed at the University of Florida demonstrated a reduction in dollarweed just by reducing the frequency of watering. {Quote}: "Monitoring moisture levels and evaluating irrigation frequency are the first steps to controlling dollarweed."

In English, that means turn off your sprinklers! Don't water if it rained recently. And it especially means to follow the rules of wise watering we've been harping on for the past 16 years: "Don't water if you've had an inch of rain within the week. Only water deeply but infrequently. Always let your plants dry out between waterings."

Now, most sources—including Clemson—agree that the best control in lawns is to start taking care of the lawn correctly…

"Gee—where have I heard that before?"

"I think that loud guy on the radio with the funny accent keeps saying it."

So, in a Northern lawn, that means never cutting below three inches, feeding only in the Spring and Fall, always returning the clippings to the lawn and—when water-loving weeds like this are present—core aerating in late summer/early fall to improve the drainage.

Ah, but our listener is in North Carolina--where she could still have a cool-season lawn, but more likely it's a warm-season variety like St. Augustine or Bermuda grass. In that case (warm season), she should cut at the recommended height for her specific variety—generally around two to two and a half inches—only feed during the warm months and aerate in the Spring or early summer.

And in flower beds? Again, first thing is to cut back on the watering. Then pull, whack, and mulch, working small sections at a time to try and regain control. And because our listener's area sounds really wet, she might want to look at modifying her layout to a rain garden design, where the beds and lawn will become less waterlogged but there will still be nice wet spots for her aquatic wildlife.

Q. Our property is marsh on two sides; it's my parent's old house, so I know for certain that the water is rising (or the rest of the town is sinking)--we get fiddler crabs in the yard! We used to have a beautiful St Augustine lawn, but the dollar weed is taking over; it even grows where it gets a saltwater bath twice a day. The only good thing is that our Chesapeake Bay retriever eats the roots I pull out. She holds the plant between her paws and eats it like spaghetti. Very funny to see! Anyway—how does someone with very little time and money to spend get the dang dollar weed out? Or is there a commercial market for the stuff? Is it edible?

---Mary in Morehead City, NC

A. Actually, it is said to be edible. Just be sure you've made a correct identification, and don't harvest it from potentially polluted waters. But more to the point in this soggy situation, St. Augustine is out; it's a plant of the past. Dollar weed is in; and it's one of the few things that these rising water levels will allow to grow there.

And for many people it's a first choice for wet areas. To quote Timber Press' "Encyclopedia of Water Garden Plants, "there is something cheerful about a plant that remains green from spring through fall and whose serrated leaves look like smiles connected at the corners."



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