Growing Concerns: Dont horse around with aggressive Equisetum
July 3, 2008 · Updated 8:15 PM
Imagine forging a path through a rain forest so deep that the very air is a humid, green haze. Theres a dense canopy of fern overhead, but it doesnt keep the constant mist from drenching hair and skin. In the distance, you hear the roar of some monstrous amphibian. You quicken your pace through a thicket of towering trees that jut stiffly from the forest floor. They resemble giant asparagus stalks topped with conical appendages. Interspersed among them are equally curious trees with graceful whorls of angled, needle-like branches.
Its the Paleozoic era, and youre in a forest of gigantic Equisetum (horsetail). They and their cousins, the ferns, are among the oldest plants on the planet. Tree-sized horsetail has been found in dinosaur-era fossil beds. The dinosaurs are long gone, but horsetail, unfortunately, is still with us.
There are many species of horsetail, but Equisitum arvense is that persistent, perennial invader of pastures, hayfields, orchards, gardens and landscapes. Known as field horsetail, it is usually considered a weed. In fact, it ranks right up there with Canada thistle, Himalayan blackberry and dandelion as the weeds gardeners most despise.
Horsetails high silica content makes it mildly abrasive. In the old days, it was nicknamed scouring rush, and was used to scrub cooking utensils, polish pewter and smooth wooden surfaces. Herbalists used it as a poultice to stop bleeding and to cure disorders of the urinary tract.
But as livestock owners know, it is also toxic, especially to horses. Most horses will avoid it, but when it occurs in hayfields, it may be accidentally mown and dried and later consumed in hay by unsuspecting animals. Children are often attracted to horsetails hollow stems, the segments of which can be pulled apart and fitted back together like a puzzle. Kids (and adults) should wash their hands after handling the plant and the stems should never be put in the mouth.
Field horsetail reproduces by both spores and rhizomes. In early spring, deep, creeping, rootstocks produce two types of hollow-stemmed plants. The first to appear is a thick, light-colored fertile stem, topped by a cone-like organ called a strobulus. When the plant reaches maturity at about a foot tall, the strobulus releases a cloud of powdery spores that germinate and form new colonies. Mission accomplished, these stems die back, and are replaced by wiry, sterile, vegetative stems. They can grow to about three feet tall, and resemble small, spindly pine trees. This plant remains until frost.
The rhizome from which both plants emerged does not die back in winter. In fact, its very much alive, exuberantly expanding in all directions. It may reside just a few inches underground, or it can penetrate pure clay up to six feet deep. The rhizomes brittle nature defies those who would dig it out. It breaks easily and every little piece can produce a new plant. It has no respect for property lines, and has caused many an unneighborly dispute.
Horsetail thrives in a moist environment, but will tolerate dry areas. It isnt particularly fussy about soil, and as the photo accompanying this article demonstrates, it will even poke up through asphalt! It prefers full sun, but youll still find it growing in shady environments. Equisitum is a survivor, and an aggressive one, at that.
Is there anything good about this plant? Well, it is bizarrely beautiful, and the short-lived fertile stems add a certain drama to floral arrangements. I have also seen them planted in containers in entryways and around water features. Although I find them attractive, Im apprehensive that the mature stems would spread spores, turning the garden into horsetail heaven.
In doing research for this article, I learned that Equisitum absorbs heavy metals from the soil. This means that horsetail may be useful in identifying and even removing toxins from contaminated land.
But as a gardener, youre probably most interested in getting rid of horsetail. Master Gardeners, myself included, will recommend the use of chemicals only when all other options are exhausted. Unfortunately, horsetail is one of the most difficult weeds to eradicate by non-chemical means.
To protect non-food crop areas from horsetail, you may choose to apply dichlobenil (Casoron) as a pre-emergent. It must be used before stems emerge in early spring, or after any existing stems have been removed.
If it comes up in your flowerbeds or shrubs where putting down plastic mulch isnt an option, you may carefully apply the herbicide triclopyr (Brush-B-Gon) to each and every horsetail stem with a small paintbrush. You must take care not to get it on desirable plants, as it is a non-selective herbicide. In driveways or other areas where ornamental plants are not an issue, the product can be applied with a sprayer. It may take several applications to kill the root systems. As always, follow label directions exactly.
Horsetail that grows in lawns should be repeatedly mowed. Eventually, it will weaken, and in theory, at least, give up.
In the vegetable garden, your efforts are limited to hoeing it out on a regular basis or using heavyweight black plastic mulch. When hoeing or grubbing, remember that new plants can grow from even tiny pieces of that immensely vital rhizome! Some gardeners cut or burn the fertile stems prior to spore formation to reduce reproduction. In the long term, good drainage and the addition of organic mulches can make the soil less desirable to horsetail.
A publication entitled Field Horsetail (PNW 105) is available for 75 cents from the Island County WSU Extension office, located in the new Law and Justice building in Coupeville (679-7327). You may also download it from www.island.wsu.edu. The direct link is wwwagcomm.ads.orst.edu/AgComWebFile/EdMat/pnw105.pdf.
Island County Master Gardener Mariana Graham invites your input at firstname.lastname@example.org.