What Is Horsetail?
This article is primarily about a plant whose botanical name is Equisetum hyemale and which is also referred to commonly as "rough horsetail" or "scouring rush." But there are, in fact, other plants in the Equisetum genus that are also named "horsetail"; one of them is discussed separately below in the section, What Is Field Horsetail?
According to the University of Maryland Medical Center (UMM), "Horsetail is descended from huge, tree like plants that thrived 400 million years ago during the Paleozoic era." It is a perennial that is evergreen (although the green color will fade some during the course of a rough winter), but this ancient plant is more closely related to ferns than to the perennials which we are most accustomed to growing in our gardens.
A non-flowering plant, it propagates itself via spores and rhizomes. Tall and skinny, you may occasionally hear people call it "joint grass" (because of the horizontal bands that run across its stems) or "snake grass," but it is not a grass. In fact, the plant is not even related to the grasses. It can, however, serve some of the landscaping functions served by ornamental grasses.
Botanists point out that, technically, Equisetum hyemale has tiny leaves fused onto its stems. But the untrained eye will notice only the attractive stems, which grow anywhere from 2-6 feet tall, depending on conditions. These stems are dark green in color at times (picking up some bronze color in the wintertime) 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." The stems, which are punctuated by nodes, largely owe their beauty to their striking black and cream-colored bands.
Native Origin, Zones, Growing Conditions
Indigenous to North America (as well as Europe and Asia), the wild habitat for horsetail plants extends from planting zones 4 to 9. They are extremely adaptable in terms of light levels, growing in full sun, deep shade, and everything in between. In terms of moisture levels in the soil, they prefer but do not depend on a soil that is at least moderately wet; they can even grow in shallow standing water.
"Aggressive," Not "Invasive," but Tenacious Either Way
Far from being fussy plants, you will probably find that your challenge with horsetails is not in growing them, but in containing them and keeping them from spreading to places where you do not want them to grow in your yard. Born colonizers, they have a strong proclivity to spread and form a monoculture. Warning: horsetail is not a plant for the feint of heart.
Such talk often evokes the term, "invasive," but, technically, a species native to North America cannot be considered invasive in North America; that label is reserved for exotic (that is, alien, foreign) species that escape into the wild and begin to displace flora native to the region in question. It is more accurate -- in a North American context -- to describe horsetail plants as aggressive spreaders.
Should You Use Horsetail as a Water-Garden Plant?
Either way, unwanted horsetail colonies are very difficult to get rid of, so be careful before you decide to grow this plant. Eradication is difficult due to its ability to regenerate from the tiniest of rhizome fragments left behind in the ground -- not unlike the dreaded invasive, Japanese knotweed.
The main uses in landscaping for Equisetum hyemale are:
- As a plant to grow on wet ground, where most ornamental plants would not survive (for example, in a swale)
- As a vertical accent for a water feature
When using them in the latter capacity, consider growing horsetail plants in containers, to minimize the chance that they will spread (unless that is what you desire). If you will be using them as a ground cover and wish to confine them to a particular spot, you can try to contain them using the sort of barrier that you would employ for bamboo. Note, however, that such practices are not guaranteed to be successful in preventing the spread of horsetails.
That is why you should ask yourself, before buying this plant, if you would be comfortable having it pop up in places on your property where you had not planned on growing it -- because that is what might well happen, despite your best efforts to restrict its spread.
It is a moderately pretty plant, but you might end up resenting it as a weed unless you have come to grips with the reality that horsetail is designed to conquer.
What Is Field Horsetail?
Speaking of weeds, the other kind of Equisetum that will be mentioned in this piece is field horsetail, also commonly called "corn horsetail" (Equisetum arvense). We can be comfortable categorizing this plant as a weed simply because it is every bit as aggressive a spreader as Equisetum hyemale, while lacking the redeeming aesthetic qualities of the latter (although it does have other uses: see below under Traditional Uses).
There are two subgenera of Equisetum, namely, the Scouring Rushes (an example of which is the E. hyemalis that we have been discussing) and the true Horsetails (an example of which is E. arvense). UMM observes that it is simple to distinguish between the two, remarking that the true horsetails "have branches, in regular whorls, giving them a somewhat bushy look. Scouring Rushes lack branches." Indeed, the branches of field horsetail give this weed the bushy appearance that invited comparisons to a horse's tail. But it is also reminiscent of the undersea denizen, maiden's hair plant (Chlorodesmis).
The landscaping at the author's childhood home is overrun with this rhizomatous perennial. It is quite possible that a rhizome of field horsetail was hidden in some loam or fill that had been brought onto the property decades ago, and that this was all the opening field horsetail needed to establish itself as a menace on the land.
Field horsetails will spread even under dry conditions (the land in the case just cited is quite dry). They lack the grace of rough horsetails, being shorter: At most, they will reach 20 inches in height, but you will often encounter specimens (stunted, perhaps, by the dryness of the earth in which they grow) that stand about 8 inches tall or less. Their color is also usually a shade of green lighter than that on E. hyemalis.
Traditional Uses for Horsetail Plants
Because of the rough texture that gives it one of its common names, rough horsetail has traditionally been used for scouring pots and pans -- thus another of its common names, "scouring rush." Meanwhile, according to UMM, field horsetail has been used medicinally going back to the ancient Romans and Greeks.
Alternative medicine experts suggest that horsetail can serve as an antioxidant and that it can fight inflammation (an extract is commercially available, which you can take as a dietary supplement).
Origin of the Names
Equisetum breaks down into two Latin words, meaning "horse" and "bristle." Flora of North America explains this derivation as "referring to the coarse black roots of E. fluviatile" (which is one of the other kinds of horsetail).
The species name, hyemale means "pertaining to winter" in Latin. The word sometimes takes other forms; for example, you will often see it spelled as hiemalis. Apparently, this species name pays tribute to the evergreen nature of the plant and the consequent interest it can lend to the winter landscape. Finally, the species name, arvense translates as "field" in Latin and perhaps refers to the fact that this weed is a common problem in farmer's fields.