Burclover

What is burclover?

Burclover is a low, cool-season annual in the legume family that turns up in lawns, pastures and along roadsides. burclover identification comes down to two things: clover-style leaves made of three toothed leaflets, and the tightly coiled, prickly seed pods that gave the plant its name. It arrived from southern Europe and became widely naturalized in the United States after farmers grew it for hay and as a cover crop.

In a lawn it is mostly a nuisance, but a persistent one. Its color, texture and growth rate don't match the surrounding grass, its flowers draw bees to places where people walk barefoot, and by late spring the dry burs jab feet and cling to clothes and pets. The seeds have tough coats that survive heat, so a patch that is allowed to seed keeps coming back season after season until that supply in the soil runs out.

Burclover identification: what to look for

Look closely in late winter or spring, when it is flowering and the first burs are forming. Get down to ground level: burclover lies flat, with every stem running out from one central root, and its leaves and pods separate it from true clovers and other look-alikes.

• Leaves: Each leaf has three rounded to oval leaflets with finely toothed edges and noticeable veins. The middle leaflet has a short stalk while the side leaflets are almost stalkless, and the center vein is frequently reddish.
• Stems: Trailing stems branch from the base and spread across the ground, commonly from 6 inches to more than 2 feet long. In thick stands they may grow upward instead.
• Flowers: Small, bright yellow, pea-like flowers sit in little clusters at the ends of the stems. Bloom usually starts around February and can run into June depending on your climate.
• Burs: The pod winds into a tight spiral of two to six coils, about 1/4 inch wide, and dries to light brown. Most carry two or three rows of prickles on the outer edge, and the prickles often end in tiny hooks.
• Seeds: Several yellowish to tan, kidney-shaped seeds sit inside each bur. They are large for such a small legume, a bit over 3/32 inch long, with hard coats.
• Seedlings: Seedlings open with oblong seed leaves, then a single rounded true leaf, and after that the familiar three-part clover-like leaves.

Where it grows in the United States

Burclover does best where winters are mild and wet and summers are hot and dry. USDA describes it as most plentiful west of the Sierra Nevada and Cascade ranges, in valleys and low foothills, and in California it grows nearly statewide up to about 5,000 feet, except in the Great Basin and the deserts. It is also a familiar spring lawn weed in Texas, where it blooms from March into May.

It likes heavier loam soils, 10 to 25 inches of rain a year and a wide soil pH range of roughly 4.7 to 8.0, and it grows in full sun or deep shade. That is why it shows up in thin turf under trees as readily as on roadsides, in pastures, orchards and alfalfa fields. Much of its spread traces back to deliberate planting: it is still used as a self-reseeding, nitrogen-fixing cover crop in orchards and vineyards and as winter forage for livestock.

Burclover look-alikes

A few plants get mixed up with it:

• Black medic (Medicago lupulina): Also a low annual with three-part leaves and small yellow flower clusters, but its pod is a small, smooth, single-seeded pod that turns brown to black. It never forms a spiny, coiled bur.
• White clover (Trifolium repens): A perennial whose creeping stems root at the joints and build spreading clumps. Its flowers are white to pale pink, its leaflets often carry a whitish mark, and it makes no burs.
• Spotted burclover (Medicago arabica): A close cousin with the same yellow flowers and spiny burs, but its leaflets carry purplish markings, while burclover's are usually plain. Extension turf guides control the two the same way.
• Yellow wood sorrel (Oxalis spp.): Oxalis leaflets are heart-shaped with a deeper notch at the tip, there is no stipule where the leaf meets the stem, and its yellow flowers have five open petals rather than a pea shape.

How to get rid of burclover

Pulling, digging and mowing: Burclover is one of the easier lawn weeds to pull because each plant grows from a single taproot. Grab the crown and pull, or slice it out with a hoe, and do it before the flowers turn into burs. Keep checking through winter and spring, because new seedlings keep emerging from seed already in the soil, and repeat wherever you reseed grass. Mowing won't solve it: the plant stays low enough to slip under the blade, and in orchards mowing trims the growth without cutting next year's seed supply. Composting or solarizing infested soil also fails, since the hard seeds tolerate heat.

Cultural control matters most, because the right conditions keep it from coming back.

• Keep turf thick. A dense stand of grass leaves little room for clover seedlings to establish.
• Feed the grass, not the clover. Yellowish grass with green clover patches points to low nitrogen, so follow a nitrogen program for your grass type, and get a soil test, because high phosphorus favors clover.
• In shrub and flower beds, spread about 4 inches of organic mulch before fall germination, or 4 to 6 inches to bury seedlings that are already up, and top it off every year.
• Woven landscape fabric under mulch can keep clovers out of beds for several years.
• Brush burs off clothing, shoes and pets before leaving an infested area so you don't seed a new spot.

Herbicides: In lawns, established burclover is best handled with a broadleaf lawn herbicide labeled for clover. Texas Extension turf guidance lists products containing mecoprop (MCPP), dicamba, or triclopyr plus clopyralid, along with combinations of these with 2,4-D; UC IPM notes that 2,4-D by itself tends to injure clovers rather than kill them. Warm-season grasses such as bermudagrass and zoysiagrass tolerate mecoprop and dicamba but not triclopyr, while cool-season lawns tolerate all of them, so match the product to your grass. Isoxaben is a preemergence option that stops annual clover seedlings when it goes down before the fall flush. In beds or open ground, glyphosate kills small seedlings but harms any plant it touches, and plants past about 3 to 4 inches often regrow after the tops burn back. No lawn clover herbicide is safe to spray over ornamental plantings. Use only products whose label covers your site, whether lawn, bed or pasture, and follow the label exactly; it is the law. If you hire someone to spray, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Keeping it from coming back

Burclover returns from seed, so the long game is draining the seed bank. Pull or treat plants every season before burs form, and expect a few years of follow-up, because the hard-coated seeds can sprout long after they fall.

Keep bare spots seeded and the lawn properly fertilized so grass, not clover, fills the gaps each fall. Mulch beds before fall rains, and brush burs off clothes and pets so you don't move seed around the yard. If you buy pasture or cover crop seed, read the tag, since burclover is sometimes included on purpose.

Questions we get about burclover

Similar weeds

Black MedicMedicago lupulinaWhite CloverTrifolium repensYellow Wood SorrelOxalis stricta