Horsetails (Equisetum species) are among the oldest plants on earth. Tree-size horsetail fossils have been found in coal beds which date back to the Paleozoic Era. Although they've become considerably smaller, with some now only a few inches tall, they have not changed significantly in shape over the centuries.
Horsetail plants have a high concentration of silica in their tissue. Sixteenth century Europeans used these scouring reeds to scrub pots and polish furniture. Native Americans and pioneers used horsetails to clean cooking utensils; some campers still use them for that purpose.
There are about 25 species of horsetails, including both annuals and perennials. The most common one in our area, field horsetail (Equisetum arvense), is a perennial. It ranges in size from 4 inches to 2 feet tall.
Horsetails are usually considered weeds when they encroach on cultivated gardens and landscapes. They're unwelcome in pastures as they can be poisonous to ruminant animals such as cows and sheep. Some people do grow horsetails deliberately though, beside water gardens or for use in flower arranging.
Horsetails reproduce both by means of spores and spreading rhizomes. Short, thick, flesh- colored stems appear in spring. The strobilus, a cone-like structure, emerges from the top of each thick stem. The strobilus bursts open when it matures, releasing spores which germinate in the soil and form new plants. Those fertile stems then die, and are replaced by hollow, wiry, sterile stems that persist until frost. Horsetails also spread by means of branching, underground rhizomes which can be found as deep as 3 feet below the soil surface. These are difficult to remove as they are brittle and break apart easily. Each part can sprout and produce a new plant.
Horsetails are difficult to eradicate without the use of herbicides. They favor damp, sandy or gravelly, shady places. Depending on where they're growing, improving drainage and fertility and increasing the organic material in the soil along with regular mowing or clean cultivation may make the site less hospitable. Digging the plants out, in all but the smallest sites, could be prohibitively difficult due to the depth and spread of the underground rhizomes.
The most efficient way to eliminate horsetails is by using a systemic herbicide such as triclopyr, the active ingredient found in some woody brush killers. Triclopyr may be used near wetlands, but it is not labeled for use in water. You must follow label directions explicitly and be sure to read the label each and every time you use the product. If you have questions about wetland use, contact your local DNR office.