Dollarweed: The Weed That Tells You About Your Water

The weed is the reading

Most weed guides treat the plant as the problem. UF/IFAS publishes an entire guide on the opposite premise — that certain weeds are instruments — and dollarweed is one of its clearest examples:

“Dollarweed (Hydrocotyle spp.) is a reliable indicator of wet environments.”

The general principle behind it:

“Certain weeds can indicate that an underlying issue is causing stress to turf or in poorly maintained planting beds.”

Clemson says the same thing from the plant’s side:

“Dollarweed is a water-loving plant that can float. The presence of dollarweed indicates that there is excessive moisture in the area.”

“Can float” is not a curiosity, it is the diagnosis. This is a plant with an aquatic habit growing in your lawn, which means the lawn is offering something close to an aquatic habitat — either because the ground holds water or because the irrigation is putting more on than the grass uses.

So the useful first question is not which herbicide. It is why is this corner wet, and the answer is nearly always one of three things: irrigation frequency, a low spot that does not drain, or a soil that holds water at the surface.

The stem is in the middle

Before anything else, make sure it is dollarweed. Clemson’s description:

“The leaves of dollarweed are round, bright green, fleshy, and look like miniature lily pads measuring 1-2” in diameter with a scalloped edge.”

And the field mark that settles it against its common look-alike:

“Dollarweed has a stem located in the center of the leaf, while dichondra’s stem is located at the edge.”

Turn one leaf over. If the stalk joins the middle of the disc, like a tiny umbrella, it is dollarweed. If it joins at a notch on the edge, so the leaf is kidney-shaped rather than round, it is dichondra — a plant some people grow deliberately as a ground cover, and one that will not tell you anything about your irrigation.

That thirty seconds decides whether the rest of this page applies to you.

The first step is not a herbicide

Clemson puts the order plainly, and it is unusual for an extension factsheet to lead with something you cannot buy:

“Monitoring moisture levels and evaluating irrigation frequency are the first steps to controlling dollarweed.”

Mississippi State goes one further, and this is the sentence worth sitting with before you buy anything: “periodic hand removal of dollarweed is often the most effective control measure.” Not a herbicide, and not from a page that avoids naming chemistry — from a publication whose whole subject is dollarweed control. On a small patch, pulling it repeatedly beats spraying it once.

They also put the irrigation advice into a number rather than a principle. Dollarweed “is most often associated with moist to wet sites”, and “previous research conducted in Florida indicates that reducing irrigation frequency may decrease dollarweed densities” — with the target being “an inch applied weekly”, which “ensures deep rooting and more drought-tolerant turf.” Frequency, not volume: the same inch delivered in one soaking rather than four sprinkles is the change that matters.

And where that is not enough, they name the structural answer instead of a stronger product: “make sure that soil drainage is adequate. Renovation of areas in order to improve surface drainage may be required.” Which is the same conclusion waterlogged lawn reaches from the drainage side.

UF’s list of fixes for wet-area weeds is almost entirely cultural:

“One can control weeds in wet areas by hand-pulling them; watering less often or with less water per irrigation event; improving drainage in low lying areas; and/or planting alternatives to turf that will thrive in moist soils.”

Three things to actually do, in order of how cheap they are.

Count your irrigation, in depth rather than minutes. Most dollarweed in a maintained lawn is an irrigation habit rather than a drainage fault. Our how often to water your lawn guide has the depths, and best lawn sprinkler covers the gauge that turns your minutes into inches — which is the only way to know whether “twenty minutes on Tuesday” is half an inch or two.

Find out whether the corner drains at all. If an area stays wet without help from you, no irrigation change reaches it — waterlogged lawn covers the test that separates a drainage problem from a watering one.

And accept the last option when it applies. UF’s final suggestion is planting something other than turf where turf does not want to be. A permanently wet low corner is a bed, not a lawn, and treating it annually is the more expensive way to reach the same conclusion.

What Alabama's own data points at

Our Alabama research records this weed as “Dollarweed (pennywort) on wet coastal ground” — and note that the state entries do not all name the same cause, which is the useful part. Some states record it on wet coastal ground, some on over-watered turf, some wherever drainage is poor. Yours names one of those, and it is the one to check first.

The soil under it: Alabama is Sandy Coastal Plain across the south, the chalky Black Belt prairie through the middle of the state, and red clay over the Appalachian foothills in the north, draining Coastal sand drains almost too fast and leaches nutrients away; Black Belt chalk clay holds water and turns to grease after a storm. On fast-draining ground dollarweed is a strong signal that the water is coming from you rather than from the soil, because this profile does not hold it. That is good news: an irrigation change should be enough, and it costs nothing.

And the water that is not yours to control: rainfall in Alabama runs One of the wettest states in the country (~55–58 in/year), with a Gulf storm season on top and a dry snap most Augusts. Humidity: Relentless from May to September — the disease pressure here is a function of nights that never dry out. On that much rain the irrigation lever is smaller than it looks — you can stop adding water and the ground will still be wet on its own schedule, which moves drainage from the optional column to the necessary one.

These are Alabama's own summer tasks from our state research — read the watering items against everything above, because the same calendar that keeps the lawn alive in August is the one that can be feeding this weed:

• Feed bermuda and zoysia monthly; give centipede iron for colour instead of more nitrogen
• Mow centipede at 1.5–2 inches, St. Augustine at 3–4 — the same deck setting cannot serve both
• Scout for mole cricket tunnelling on coastal lawns after evening rain

Local timing: the post-emergent window in Alabama is April–May and September, and check every label against centipede before it leaves the shelf, and the dominant lawn grass is Centipede — which decides which of the herbicides below you can actually use. Alabama Extension Lawn & Garden at Alabama Cooperative Extension System (Auburn University and Alabama A&M) publishes the local version, which matters on atrazine specifically because its restrictions are not uniform.

Then the herbicide, by grass

Clemson’s selection is by turf species, not by weed, and getting it backwards is how people damage the lawn they were treating:

And the timing:

“Herbicides should be chosen according to turf species and applied in late spring (after full spring green-up of the lawn) when weeds are small.”

Both halves of that sentence matter. After full green-up, because a warm-season lawn still coming out of dormancy is spending stored reserves and cannot metabolise the stress — the same rule that governs the first nitrogen application in zoysia grass care. And while weeds are small, because a young dollarweed plant has less stored energy underground than an established colony, so the identical application does more work.

We do not stock an imazaquin product. Clemson names it for bermuda and zoysia and we have nothing to card — the three-way covers the same two grasses on the same list, so this is a gap in our catalogue rather than a gap in your options.

And on the weed-and-feed route: the atrazine-based southern weed and feed products do list dollarweed, and they are two jobs on one calendar. The herbicide wants late spring after green-up while the plants are small; the nitrogen wants a lawn already growing. Those dates are close on St. Augustine and easy to get wrong. Our when to weed and feed guide works through the compromise; the short version is that separating them costs one extra trip and removes the whole problem.

It rarely arrives alone

UF’s wet-indicator list does not stop at dollarweed. Also named as species commonly found in moist or wet soils: sedges, doveweed, spreading dayflower, Virginia buttonweed and Asiatic pennywort.

So a corner with dollarweed and nutsedge in it is not two weed problems. It is one water problem with two symptoms — and worth knowing that fixing the water removes the invitation but not the plants already there. Sedge in particular needs its own chemistry, because nothing in the table above touches it.

That is also the argument for treating the cause first. Every one of those species would otherwise need its own herbicide, its own timing and its own label check, and they all germinate into the same wet ground.

The neighbouring decisions

How often to water your lawn is the irrigation side and the first thing to change, waterlogged lawn separates a drainage fault from a watering habit, how to get rid of nutsedge covers the companion weed that needs different chemistry, st augustine grass care is the grass most affected by this one, and best weed killer for lawns covers how the three-way chemistry works on broadleaves generally.

Among the other broadleaves, the useful comparison is which condition each one is reading. Broadleaf plantain reads compaction and clover reads low nitrogen, the way this one reads water — while chickweed and henbit and oxalis are mostly reading thin turf and open ground. Creeping charlie and wild violet are the two that share this weed’s real problem — a waxy or shaded leaf that shrugs off a single application — and dandelions are the easy case that makes all the others look harder than they are. If you would rather not spray at all, the weed pullers work on taprooted broadleaves but not on a creeping mat like this one.

The honest summary

Dollarweed is telling you the ground is too wet, and it is a reliable enough instrument that UF publishes it as one. Confirm it by the stem joining the centre of the leaf rather than the edge. Then fix the water before you buy anything: count irrigation in inches, find out whether the low corner drains, and accept that a permanently wet spot is a bed rather than a lawn. Only then choose the herbicide by your grass, in late spring after full green-up while the plants are small. Do it in that order and you treat this once. Do it backwards and you treat it every year.