Q. What is the most efficient way to eradicate horsetail?
Equisetum arvense, commonly called field horsetail, looks like a prehistoric survivor. This perennial can be one of the toughest weeds to manage. The ancient genus Equisetum was the dominant plant group during the Carboniferous Period, 359-299 million years ago.
The plant has fleshy tubers that grow along the underground rhizomes singly or in pairs, positioned from a few inches to six feet deep in the soil. The tubers store carbohydrates produced by photosynthesis, allowing field horsetail to have amazing regenerative capability and making it difficult to control.
Two types of stems grow from the rhizome annually. Tan-to-white fertile stems, resembling short asparagus sprouts, grow up to a foot tall in early spring. These stems are unbranched and leafless, topped by a spore-bearing cone up to four inches long. Since they lack chlorophyll, these fertile stems die shortly after releasing their spores. After the fertile stems die back, sterile stems arise and grow about two feet tall. These stems are grooved and hollow, covered with whorls of feathery leaves that make the plant look like a green bottle brush or a miniature conifer.
Controlling Field Horsetail
Control options include repeated mowing or mechanical removal. Although it can take years, dedicated removal of the sterile stems depletes the carbohydrate reserves and will eventually exhaust the rhizome. Field horsetail grows best in full sun and so can also be controlled by shading. Mechanical removal of the stems followed by mulching with black plastic can also be effective. But one reference says that smothering the plants with black plastic or other mulch is not effective, as horsetail thrives when conditions are wet, dark and low in oxygen. Sprouts emerge when the plastic or mulch is removed no matter how long the plant has been covered. Tillage can make the problem worse by spreading the rhizomes and/or tubers.
Although it is not a quick solution, horsetail can be controlled by eliminating top growth repeatedly, preventing spores from germinating. Cut off the green growth above ground whenever it appears; the plant will eventually die out.
If you are purposely cultivating a patch of horsetail, you can control its spread both by repeatedly removing shoots in areas where you don't want them and by removing the shoots that produce the spore-filled cones.
The most effective, though uncommon, approach to eliminating horsetail is to alter the conditions in which the plant is growing, making the site inhospitable to horsetail. Horsetail thrives in wet conditions, so improve drainage by filling in low spots that hold water and installing drainage ditches, small swales, or dry streambeds to divert water. The plant prefers poor, infertile soil, so boost soil nutrient content with chemical fertilizer or (preferably) organic compost, aged manure, or fish emulsion. Raising the soil's pH is a key element in a horsetail-control plan as well, since the plant prefers acidic soil. Add agricultural lime to the soil two weeks before or after the fertilizer for best results. Though it may take up to five years, the plants will go away on their own using this tactic. Keeping the greenery and spore cones cut hastens success.
Hope this helps.
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- Courtesy of NYBG Plant Information Service