Horsetail (Equisetum hyemale), also called rough horsetail or scouring rush, is a non-flowering evergreen perennial. It has vertical green stems with horizontal bands, similar to bamboo, but the stems are skinny, like tall grass. Like ferns, horsetail reproduces through spores rather than seeds, as well as underground rhizomes. However, horsetail is not related to bamboo or grass or ferns. Its species dates back to Paleozoic times, some 350 million years ago.
Horsetail grows in wet conditions and can even grow in standing water. For this reason, it is commonly used to decorate water gardens or swampy areas where few other plants can survive. It's also commonly grown as an accent along borders or in large patio pots, similarly to how ornamental grasses are used.
Horsetail spreads via rhizomes and spores and is such an aggressive spreader it would likely be considered invasive if it weren't native to North America (as well as Europe and Asia). It is more accurate (in a North American context) to describe horsetail plants as very aggressive spreaders. This is an important consideration when planting horsetail anywhere outside of a pot. To prevent it from taking over your garden or other planted ground, it's advisable to use soil barriers or another form of containment.
Botanists point out that Equisetum hyemale has tiny leaves fused onto its stems. But the untrained eye notices only the attractive stems, which grow anywhere from 2 to 6 feet tall, depending on conditions. These stems are dark green at times (picking up some bronze color in winter) and hollow. Tiny ridges run vertically along the stems and contain silica, giving them the rough feel that earns the plant the common name, rough horsetail. Early Americans used this plant for scouring pots and pans.
Horsetail is usually planted in early spring, though it will survive planting at almost any time. This is an extremely fast-growing plant that achieves full height within a matter of weeks. Under ideal circumstances (constantly moist soil), a clump of horsetail can spread more than 100 feet within a year.
|Botanical Name||Equisetum hyemale|
|Common Name||Horsetail, rough horsetail, scouring rush|
|Plant Type||Evergreen perennial|
|Mature Size||2–6 feet tall, 1–6 feet wide|
|Sun Exposure||Full sun to part shade|
|Soil Type||Moist, well-drained|
|Soil pH||6.5 to 7.5 (slightly acidic to slightly alkaline)|
|Bloom Time||Non-flowering plant|
|Flower Color||Non-flowering plant|
|Hardiness Zones||4–9 (USDA)|
|Native Area||North America, Eurasia|
|Toxicity||Non-toxic to humans, toxic to grazing animals|
Far from being fussy plants, often the challenge with horsetails isn't in growing them but in containing them and keeping them from spreading to places where you don't want them to grow. They are born colonizers with a strong tendency to spread and form a monoculture. On the other hand, if you'd like the plants to fill an area that is unfavorable to most other plants, such as in a swale, the spreading ability of horsetail is desirable.
To contain horsetail planted in the ground, you can install plastic barriers in the soil, the same method you can use to contain invasive bamboo. Another option is to plant the horsetail in a deep pot buried in the ground. However, because horsetail spreads not only by underground rhizomes but also spores, containment is challenging.
Horsetail is extremely adaptable to various light levels, growing in full sun to part shade, but preferring filtered shade, such as found on forest floors beneath tall trees.
Horsetail prefers poor, sandy, gravely soil that is frequently wet. The more fertile the soil, the slower it grows. When growing horsetail in a container, consider adding gravel or sand to potting mix to give it the perfect medium it enjoy
In terms of moisture level in the soil, horsetail prefers a soil that is at least moderately wet. It can even grow in standing water up to a depth of about 4 inches. It's well-suited for rain gardens and other areas that may periodically flood.
Temperature and Humidity
Horsetail plants prefer high humidity for several hours a day and thrives in low light. Winter care is not a concern, as it is hardy to USDA zones 3 to 11, although the bright green of the stems may fade during cold winters.
In general, horsetail plants do not like particularly rich or fertile soil, so fertilizing should not be necessary.
Is Horsetail Toxic?
Horsetail is not toxic to humans; in fact, it has been used in a variety of folk remedies and has been studied as a source of modern medicines. However, all varieities of horsetail contain thiaminase, a compound that can break down vitamin B1 and cause convulsions and death in horses and other grazing animals. There are no reports of this plant causing problems in dogs and cats, however.
Although there are no cultivars of Equisetum hyemalis, there are several related species also known as horsetail.
- Equisetum arvense is commonly known as field horsetail or corn horsetail. This is generally categorized as a weed because it is every bit as aggressive as Equisetum hyemale but lacks its redeeming aesthetic qualities. Field horsetail can grow up to 20 inches tall, but it's often stunted by the dryness of the earth in which it grows, so that it reaches only about 8 inches tall or less. It is usually a shade of green lighter than that of E. hyemalis. Many landscapes become overrun with field horsetail; it will spread even under dry conditions.
- Giant horsetail (E. giganteum) is a Central- and South-American native hardy only to zone 8. Grow it in full sun to part shade. Its selling point is that it can become 10 feet tall or more.
- Variegated horsetail (E. variegatum), by contrast, is a shorter (6 to 18 inches), hardier plant, being native mainly to the wetlands of the northern U.S. and Canada. It's termed "variegated" because its black-and-white sheaths (on otherwise green stems) show up better than those on E. hyemalis. Grow it in full sun to part shade.
It's rare that a homeowner wants to propagate horsetail, since containing or eradicating this fast-spreading plant is more often the challenge. However, if you do want to share plants, it is an easy matter to cut away portions of the rhizomatous root clumps and replant them wherever you want. Spring is the best time to perform this action.
Horsetail produces naturally through spores rather than seeds, and the tiny volunteer plants can also be dug up and replanted elsewhere.
Common Pests/ Diseases
As befits a plant with a reputation for invasiveness, horsetail has no serious threats from pests and diseases. The main challenge is to keep this plant under control or eradicated it where it is not wanted. Horsetail can even extend its roots under sidewalks, garden walls, and driveways, so elimination requires that you carefully dig up and remove all root pieces.
It may also be possible to eradicate horsetail gradually by cutting the reed-like stems back to ground level as they appear. This can take several seasons before the plants surrender and die completely.
Finally, you can use a systemic herbicide containing triclopyr, which will kill horsetail. It may, however, take multiple applications before you completely eradicate the plant.
Horsetail and Scouringrush. University of California Weed Research & Information Center.
Riet-Correa, Franklin, Medeiros, Rosane MT., Pfister, James A., Mendonca, Fabio S. Toxic Plants Affecting the Nervous System of Ruminants and Horses in Brazil. Brazilian Journal of Veterinary Research, 37,12,2017, doi:10.1590/S0100-736X2017001200001