If you fight against invasive goathead weeds (Tribulus terrestris), you are likely familiar with why they are also called puncturevine crops: The sharp, sticky seedpods easily pierce skin and substances much thicker than the skin, including — possibly — cardboard. Still, cardboard can be a way to kill these plants that are invasive, as long as it’s used.
Goathead grows in every state. The pesky plant dies at the first frost but reseeds prolifically, also in regions which don’t see temperatures, annually, it continues to sprout and grow. Before it sets seedpods the best method to kill goathead is to pull it out by hand. This may not be a sensible option, because it spreads so quickly. One option is to smother the weeds if you do not need to resort to chemical weedkillers.
Weeds require air, water and light to develop, and goathead is no exception. Block its accessibility to those things, and it will fail to grow — depending on how well access is obstructed. Mulch alone will leave holes which will still allow light and water to work their way through, and gently laying a single sheet of cardboard atop a goathead plant won’t work well, if at allNot only will lighting, water and air continue to be able to get inside, but the cardboard will likely dismiss when the wind picks up. The cardboard has to be implemented in this manner that the goathead plants are smothered.
To kill and interrogate goathead several sheets of overlapping cardboard across the crops, then cover that with a thick layer organic material, such as bark or straw, to weigh down it. The mulch, including the cardboard, ought to be a minimum of three inches thick. As time passes, rain will make the cardboard decompose, but with this technique can still kill up to 75 percent of the weeds at the first year, advises Birds & Blooms magazine.
Control Over Time
Leave the cardboard a year — longer if you do not need to use the area for whatever else. Since seeds are viable in the soil for five decades, you will most likely have to reapply the cardboard after it’s decomposed, and mulch. The seeds are gone or dead, till the ground, once you’re certain — cardboard provides nutrients to the ground, and you’ll have a nice, rich patch of dirt in which to develop plants that are new.