This Toxic Weed is a Colorado Gardener’s Worst Enemy

Tending to a garden during the summertime is a rewarding hobby for many Coloradans. Watching fruits, flowers, and vegetables sprout from seeds is both exciting and satisfying. And while it's not always the most fun part of gardening, having one does mean keeping the plot of plants free of weeds.

Puncturevine is arguably one of the most annoying weeds a Colorado gardener may encounter. This noxious weed is sometimes called “goat head” due to its unique appearance. However, unlike the cute and lovable farm animal, this plant is anything but. Noxious plants can destroy entire ecosystems once spreading to an area.

Puncturevines' five-petaled flowers appear in July through October. Although the dainty yellow flowers are pretty, it's the seeds that come afterward that can cause major damage. Each flower node will produce a fruit, at maturity the fruit will break into five seed capsules. The seeds are found in hard spiny burs which develop once the weed is done flowering.

Measuring about one-half inch wide, the seed capsules can cause injury to humans, animals, and bicycle tires. The small spikes hurt when stepped on and are extremely prickly when handled. Goat heads can be also found in hay, which could cause injury to actual farm animals. The stems are trailing and can grow up to six feet long.

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Native to Europe, puncturevine eventually made its way to Colorado. It's most commonly found in the eastern part of the state, at elevations below 6,500 feet. The mat-forming weed thrives in disturbed soils, pastures, orchards, and vacant lots.

As an invasive summer annual, ascending puncturevine is a serious competitor with crops. They can only reproduce from seed, but these seeds can stay viable for 4 to 5 years.

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Puncturevine plants can be controlled by pulling them out of moist soil, just make sure to wear gloves! Another successful way to control goat heads is with a particular seed-feeding weevil, however, pulling them out is much easier. The weevils are used more for larger acreages that have too many puncturevine to pull or treat. Plant experts at Colorado State University explain that laying down thick mulch can also be an effective way of reducing populations of puncturevine. Herbicides can also provide resistance if applied when the plants are young and small.