Weed Watch: What’s that sprawling plant with white, cross-shaped flowers in my summer garden?

By Mary Free, Extension Master Gardener 

Both its Latin name, Diodia virginiana, and common name, Virginia buttonweed, identify this plant as a Virginia native. This mat-forming perennial likes moist to wet soil and in the wild typically grows in marshlands, wet meadows, and muddy waterway shores. It attracts small bees (although not in great quantities), provides habitat to some invertebrates, and, in its decomposed form, supplies food for aquatic life.

Despite its wildlife value, though, Virginia buttonweed is not a welcome addition in a cultivated landscape, such as a lawn or ornamental bed. In addition to its aggressive sprawl, it is the host of flea beetle Strabala rufa, a herbivorous insect that can damage garden and agricultural plants.

Because of its prostrate spreading habit, Virginia buttonweed’s splitting branches can creep virtually unnoticed through turf grasses and ornamental ground covers and, if left unattended, can crowd out other plants. Indeed, from the mid-Atlantic southward, this plant is considered a troublesome weed. It can crop up in poorly drained or low points in a lawn, or in gardens that remain excessively wet, so it is important to correct drainage problems and water lawns and plants only as needed. Frequent, shallow watering will only encourage its growth.

The quadrangular, reddish or green stems of Virginia buttonweed are either glabrous or hirsute on each edge with straight or wavy hairs. They can radiate out from the woody root crown up to two feet. The simple, pinnate leaves are sessile and opposite on the stem with a lanceolate shape, minute teeth along the margins, and sheathing stipules. They may appear mottled yellow due to a virus (Diodia Vein Chlorosis Closterovirus). If you failed to identify the plant as it emerged or its stems spread, the half-inch, cross-shaped, white flowers that appear in leaf axils along the stems in summer and fall might draw your attention. Flowers have four pubescent petals, four stamens, and a two-branched, flattened, filiform style. Fruits are ridged schizocarps.

Unfortunately, by the time its cross-shaped flowers adorn the stems (starting in June), Virginia buttonweed may be firmly established and extremely difficult to remove. Unlike native American burnweed, whose shallow, fibrous root system allows it to be easily removed by hand alone, Virginia buttonweed has a long taproot, which dives down deep into the soil as well as numerous secondary roots that grow out horizontally under the spreading stems. Even with the aid of a hori hori knife or small shovel, you may not be successful and remnants left in the ground could grow new plants. If you decide to try manual removal, it is best to tackle it when the soil is moist. Even young plants can have taproots three-to-four times as long as the stems are high.

In an ornamental bed, a thick layer of mulch can discourage its reestablishment. Better yet, first lay down plain, uncoated cardboard sheet(s) with tape, staples, or labels removed (use layers of newspaper in smaller areas), making sure water can get to the roots of any nearby plants. Soak the cardboard thoroughly, then apply a layer of natural mulch on top. The cardboard will suppress the weeds and decompose in six-to-twelve months, adding organic material to the soil.

For healthy lawns, set the mower blades at the highest height for your particular grass species. Lawn mower blades set at the lowest height do not affect the growth of Virginia buttonweed and may even aid in its spread if stem fragments or seeds root. In areas where it grows, collect clippings and dispose of them in the trash to reduce its spread. If you need to use chemicals to remove Virginia buttonweed, carefully follow the directions on the label and use personal protective equipment. Contact your local or Virginia Cooperative Extension office for herbicide control recommendations for Virginia buttonweed. In Arlington and Alexandria contact the Extension Master Gardener Help Desk at mgarlalex@gmail.com or at 703-228-6414 from 9 a.m. to 12 noon, Monday through Friday.

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References

Diodia virginiana. Last Modified 11/08/2024. Missouriplants.com. Missouri Native Plant Society.

Enroth C. June 25, 2021. The disadvantages of landscape fabric. Good Growing. Illinois Extension. University of Illinois Urbana-Champaign.

Keener BR, Diamond AR, Barger TW, Davenport LJ, Davison PG, Ginzbarg SL, Hansen CJ, Spaulding DD, Triplett JK, Woods M. 2025. Diodia virginiana. Alabama Plant Atlas. [S.M. Landry and K.N. Campbell (original application development), Florida Center for Community Design and Research. University of South Florida]. University of West Alabama, Livingston, Alabama.

Olsen E. 2022. Know A Weed: Virginia Buttonweed. Virginia Cooperative Extension, Henrico Horticulture.

Weakley AS, Ludwig JC, Townsend JF. 2012. Flora of Virginia. Botanical Research Institute of Texas, page 902.