Spotted Spurge: The Weed Nobody Knows

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Spotted spurge (Euphorbia maculata). Photo: plantsam.com

In my area, this has been a banner year for spotted spurge (Euphorbia maculata, formerly known as Chamaesyce maculata), also called spotted euphorbia, spotted sandmat and milk purslane, a low-growing, spreading annual weed most often seen in thin lawns, along roadsides, growing from cracks in sidewalks and in waste ground and elsewhere in sunny spots of disturbed soil. 

We’ve had a very hot, dry summer, something lawn grasses detest, and that allowed spotted spurge, normally a fairly discreet weed in my area, to take over, even covering vast stretches of burnt-out lawn. As a result, I’ve been receiving photo after photo of this plant, asking what it is. Although very adaptable, it does seem to do especially well in poor, compacted soil in full sun. Where it thrives, it outcompetes other plants, like lawn grasses.

Spotted spurge can make an attractive, if temporary, groundcover. Photo: plants.ces.ncsu.edu

Spotted spurge is actually quite attractive, making a nice, thick carpet, with creeping stems radiating outwards from a deep taproot up to 2 feet (60 cm) long, leading to some people to wonder if it couldn’t be used as a groundcover or even a lawn substitute. However, its annual nature, that is, dying in the fall and sprouting anew in mid-spring from seeds left in the ground, means it would only successfully cover ground after it has filled in, from midsummer to late fall. In spring and early summer, it would still be too small to make an effective groundcover … and what use is a groundcover that leaves the ground uncovered for 6 or more months of the year?

Close-up showing the leaves, tiny flowers and seed capsules. Photo: http://www.inaturalist.org

The paired leaves, lanceolate oval in shape, about 1/6 to 2/3 of an inch (4–17 mm) and with barely any petiole, are mid-green, usually smooth with a reddish margin and an elongated purple spot in the center. They’re borne on pink to maroon somewhat hairy stems that don’t root at the nodes. The purple spot that gives the plant its name is not always present and, if not, this plant could be confused with other closely related ground-hugging spurges like prostrate spurge (E. prostrata), sprawling spurge (E. humifusa), ridge-seed spurge (E. glyptosperma) and matted sandmat (E. serpens), all are best told apart by their broader leaves. Also, spotted spurge is much more widespread than its relatives.

As for the flowers, they are tiny and insignificant, pink fading to white, and growing in clusters at the leaf axils. Get out your magnifying glass if you want to study them! 

Spotted spurge usually grows perfectly prostrate. Photo: aggie-horticulture.tamu.edu

Spotted spurge usually remains very low-growing (under 1 inch/2.5 cm), so can’t be controlled by mowing, but can reach 4 inches (10 cm) if surrounded by competing plants. It usually spreads to about 18 inches (45 cm) in diameter.

The milky white sap helps identify spotted spurge. Photo: thegreenthumb20.wordpress.com

To distinguish spotted spurge from other small-leaved creeping weeds like knotweed (Polygonum aviculare) or purslane (Portulaca oleracea), just break off a piece of stem. Only the spurge produces white latex from its wounds. As with most euphorbias, the latex is irritating to the skin and poisonous if igested. Some people have fairly serious allergic reactions to the sap, so if you’re doing any hand-pulling, wear gloves.

The tiny flowers produce even tinier brown seeds. Plants only five weeks old already produce viable seed and produce them continuously until the the death of the plants in the fall. Each plant produces thousands of seeds per year and they can remain dormant for years until appropriate conditions appear. They readily stick to shoes and animal fur and can thus be transported over great distances.

Distribution of spotted spurge in North America north of Mexico. Photo: USDA

As a result, this plant, originally thought to be native to the American Midwest, has spread throughout that country and north into Canada and is now found, although sometimes in a still localized fashion, on all continents except Antarctica.

How to Control Spotted Spurge

Knowing what the spotted spurge wants can help guide you in controlling it. 

It needs light to germinate, so won’t germinate under mulch nor in a thick lawn. In flower beds and vegetable gardens, just keeping the plants well mulched is therefore all the control you’ll likely need.

As for lawns, anything that will help yours grow better (appropriate watering, fertilizing, mowing, etc.) will hinder spotted spurge.

Spotted spurge has completely overtaken this drought-weakened lawn. Photo: Jocelyne Gilbert

If your lawn is thin, which would allow spotted spurge seeds to germinate, consider topdressing with 3/4 to 1 inch (2 to 2.5 cm) of quality topsoil (spurge seeds won’t germinate if covered with more than 1/2 inch of soi), then overseeding with quality grass seed or clover. This will help thicken the lawn and make it unattractive to spotted spurge (and indeed, to most lawn weeds). Early fall is the best time to topdress and overseed.

Hand pulling is one way of removing spotted spurge from paving stones. Photo: Harry Rose, Flickr

Hand-pull plants wearing gloves, taking care not to get the sticky sap in your eyes. Weeding a day after a thorough rain or watering will make the plant easier to pull out. You need to extract at least the top part of the root; otherwise it will grow back from the base. Hand weeding, obviously, will be most effective when carried out early in the season, when the plants are small with still-shallow roots, before they start producing seeds.

Avoid purchasing nursery plants with spotted spurge growing in the pot.

Preemergent herbicides like corn gluten meal can be effective, but only if applied just before the seeds germinate (they start to do so at when the soil reaches about 60 ° F [16 ° C]). Carefully follow instructions: these products will have no effect if not applied properly. 

Lawn care companies may still be allowed to spray certain lawn herbicides on home lawns. Photo: http://www.solutionsstores.com

In most areas, lawn herbicides designed to kill broadleaf weeds but not lawn grasses are no longer available to home gardeners, but lawn care companies may still have access to a few of them and most will control spotted spurge.

Spot herbicide treatments with non-selective herbicides, ones that kill a wide range of plants, will usually be effective when applied to spotted spurge and are useful in controlling it in patios and sidewalks. They can be used in lawns as well, but since they also kill most lawn plants, must be used with great care. 

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Spotted spurge: a mystery weed no more!