How do I get rid of horsetails?

A frequent question to the Gardening Advice Line written by the Vancouver  Island Master Gardeners Association volunteers.

Question:  How do I get rid of horsetails?

Equisetum arvense (Horsetails) is an herbaceous perennial plant in the Equisetidae (horsetails) sub-class, native throughout the arctic and temperate regions of the Northern Hemisphere. It has separate sterile non-reproductive and fertile spore-bearing stems growing from a perennial underground rhizomatous stem system. The fertile stems are produced in early spring and are non-photosynthetic, while the green sterile stems start to grow after the fertile stems have wilted and persist through the summer until the first autumn frosts.  Rhizomes can pierce through the soil up to 6 feet (1.8 m) in depth. This allows this species to tolerate many conditions and is hard to get rid of even with the help of herbicides.

Answer:

Cut back as much of the weed as you can in early spring, before the pinkish-yellow domes that contain the spores ripen. Work carefully to avoid spreading the spores, and place all debris into a sealed plastic bag to dispose of it.

Another way to eliminate horsetail is by preventing it from carrying out photosynthesis. In other words, by cutting off its only supply of energy: sunlight. If you keep its leaves from being exposed to the sun, the plant will quickly stop spreading and will eventually exhaust itself and die.  If you ever decide you do want to try to control horsetail by cultivating the soil, at least make sure you clean your tools before using them in another area, otherwise you risk spreading sections of rhizomes or tubers by accident. The rototiller can be the horsetail-haters worst enemy on this level: not only does it slice the rhizomes into numerous small pieces and spread them hither and yon, but some almost always stick to the blades, transporting them to the next section of garden. A rototiller really needs a good cleaning after each use.  Another reason that cultivating doesn’t work is that horsetail tubers tend to be produced deep in the ground, up to 5 feet (150 cm) down, well out of range of cultivation tools.

Do note that horsetail is less likely to become established in dry soils. You see, its wind-blown spores will only germinate under moist conditions. However, once the plant is established, it will readily tolerate dry conditions, although it will grow more slowly under dry conditions than in moist ones. Typically the home gardener accidentally carries a section of rhizome from a moister setting to a drier one, sometimes in soil purchased from a nursery, leading to a new infestation.

In a garden watered regularly for the benefit of other plants, horsetail will be very much at ease and will spread rapidly.

Horsetail is resistant to Roundup, can survive with very little light or oxygen and has deep roots, so it's extremely hard to kill. Some herbicide, or a sedge and nutgrass product such as Sedgehammer, can eliminate horsetail completely however these products are not recommended or approved for usage in British Columbia.

References:

• Laidback Gardener 'How to Really Control Horsetail', and
• Gardening Channel 'How to Grow (or Get Rid of) Horsetail Plant'