Stepping barefoot on a sharp, dry spike in the lawn is a common and frustrating experience caused by specialized seed pods called burrs. These spiky structures are produced by common turf weeds, and their primary function is to secure the plant’s next generation. Understanding that these are reproductive parts, not random thorns, is the first step toward managing the problem. The sharp points cause discomfort to people and pets, often making the lawn unusable.
Identifying the Spiky Culprits
Identifying the specific weed responsible is necessary because control methods differ significantly between species. One common offender is Lawn Burweed (Soliva sessilis), a winter annual that forms low-growing, fern-like rosettes. This plant germinates in the fall and remains inconspicuous until early spring when it produces small, spine-tipped burrs in the leaf axils. These burrs harden as the plant dies back in late spring or early summer, leaving painful spikes scattered across the turf.
Another widespread nuisance is Sandbur (Cenchrus species), a grass-type weed and a warm-season annual. Sandbur plants often blend into turfgrass, growing in tufted, sprawling mats, particularly favoring sandy or disturbed soils. Its burrs are spherical or oval, thickly set with stiff, sharp spines, and are formed in clusters on a spike-like seed head from mid-summer through fall. Unlike Lawn Burweed, the Sandbur’s entire seed head detaches as a spiky, multi-barbed ball.
A third troublesome plant is Puncture Vine (Tribulus terrestris), sometimes called goathead, a summer annual that grows as a dense, mat-like ground cover. The plant features small, yellow flowers and leaves made up of hairy leaflets. Its fruit is a hard, woody structure that splits into five wedge-shaped burrs, each equipped with two to four stout spikes capable of flattening bicycle tires. These burrs typically begin appearing in late spring and continue throughout the summer months.
The Biological Purpose of Burrs
The existence of these sharp, clinging structures is an evolutionary strategy. Burrs represent a form of seed dispersal known as epizoochory, which is the movement of seeds by external attachment to animals. The hooks and spikes are adapted to catch onto the fur of mammals, the feathers of birds, or the clothing and shoes of humans.
This “hitchhiking” mechanism allows the plant to scatter its seeds over a much wider area than if they simply dropped to the ground. Dispersal away from the parent plant reduces competition for light, water, and soil nutrients, increasing the likelihood that the next generation will thrive. The tough, woody casing of the burr also provides physical protection for the seed.
For annual weeds, the burr is an integral part of their life cycle, serving as a protective vessel until the next growing season. For instance, the Lawn Burweed plant dies after the burrs mature, but the sharp burrs remain on the ground, shielding the seed throughout the summer. Similarly, the seeds of Puncture Vine can remain viable, protected by their armor-like burr, for up to seven years in the soil.
Strategies for Control and Eradication
Eradication requires a two-pronged strategy: immediate removal and long-term prevention. Manual removal is most effective for small infestations, but it must be done before the burrs fully harden. This timing is typically late winter or early spring for Lawn Burweed, and early summer for Sandbur and Puncture Vine. Once the spines are hard, killing the plant will not remove the existing spiky hazard.
For larger areas, chemical control is often necessary, utilizing both pre-emergent and post-emergent herbicides. Pre-emergent herbicides are applied to the soil before seeds germinate, preventing the problem before it starts. Since Sandbur and Puncture Vine are summer annuals, a pre-emergent application in early spring, before soil temperatures rise, is effective.
Lawn Burweed, as a winter annual, requires a pre-emergent application in the fall (late September or October) to stop seeds from sprouting. Post-emergent treatments, which kill actively growing weeds, are best applied during the weed’s most vulnerable, small stage. For Lawn Burweed, this is in the cooler winter months of December through February, before the spines develop.
Maintaining a dense, healthy turf is the most effective long-term cultural control practice, as thick grass crowds out opportunistic weeds. Proper fertilization, correct mowing height, and adequate watering promote a vigorous lawn that naturally outcompetes these low-growing annuals. Bagging grass clippings after burrs have formed is also recommended to prevent the mechanical spreading of the seeds.