Common Horsetail (Credit: B. Klinkenberg)
The truth is, weeds are not always invasive species, despite their ability to cause many issues of their own. The two terms are often used interchangeably because of their many shared characteristics, when in fact, weeds are just plants growing where they are not wanted – including native species! Certainly, the ancient, native, and (sometimes) weedy Horsetail illustrates this circumstance best.
Horsetails are living fossils and among the oldest surviving vascular plants on earth, with their existence dating back at least 300 million years. During the late Devonian (~416 – 359 million years ago) and Carboniferous periods (~359 – 299 million years ago), large horsetail trees, called Calamites, grew 18 m tall, creating a dense, forested landscape. As the climate changed, these plants shrunk to appear as they do today.
Most of us are familiar with these green vegetative shoots. Distinctly, Horsetails have hollow, grooved, and jointed stems. At each joint, it grows tiny leaves and whorls of green, thin branches. Additionally, its siliceous ridges create a distinctly rough outer texture. They are commonly found in groups, as Horsetails grow from an extensive rhizome (root) system.
Giant Horsetail (Credit: V. Skilton)
Several Horsetail species, such as Common Horsetail, produce both sterile and fertile shoots. Fertile plants appear before the sterile ones and are easily identifiable by their pale, unbranched stem and cone-like structure (strobilus) at the tip. The cone contains many small hexagons that each produce thousands of tiny spores. When spores are released, they grow new plants with extensive rhizomes.
While gardeners may feel exasperated by the presence of Horsetails in their garden beds, the oft-unwanted native Horsetail was not always considered a weed. Its rough texture was used by many as an abrasive for polishing a variety of tools and wooden objects. In addition, Horsetail was harvested by many Indigenous groups and used for both medicinal and edible purposes. For instance, Saanich people believed that the shoots were good for the blood, while Squamish people used the hollow stems of Giant Horsetail to drink water.
However, now, Horsetails are generally regarded as weeds since populations have become unwieldy, as the species can tolerate disturbance, withstand a wide range of soil conditions, and form deep rhizomes. Indeed, colonies often form in ditches, swamps, banks of creeks and rivers, abandoned fields, backyards, and sandy areas. In addition, ingesting large quantities of Horsetail can be toxic to wildlife, livestock and humans, causing weakness and death.
Scouring Rush (Credit: Curtis Bjork)
Unfortunately, Horsetail’s extensive root system makes it futile to pull stems or dig out roots, and chemical treatment seems to be relatively ineffective. To temporarily reduce growth, you can cut fertile stems before spore formation; if bylaws in your area allow it, some herbicides can also be effective. For long-term control, treat infested areas by improving drainage, raising pH, increasing soil fertility, and seeding with native and competitive, perennial grass species.
Undoubtedly, this plant can be a nuisance. But, its rich history reminds us that wonders are all around – in ordinary places too! Who knows what other treasures are right around the corner…
References
- Biodiversity of the Central Coast, Common Horsetail, https://www.centralcoastbiodiversity.org/common-horsetail-bull-equisetum-arvense.html
- Comox Valley Naturalist, Horsetail and Scouring Rush, https://comoxvalleynaturalist.bc.ca/featured-plant-horsetail-and-scouring-rush/
- Electronic Atlas of the Flora of BC, Equisetum arvense, http://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Equisetum%20arvense
- Government of British Columbia, Field Guide to Noxious and Other Selected Weeds of BC, https://bcinvasives.ca/wp-content/uploads/2021/02/Field_guide_to_Noxious_Weeds_11th_2021.pdf
- Government of Maine, Controlling Horsetails, https://www.maine.gov/dacf/php/gotpests/weeds/factsheets/horsetail-swanson.pdf
- Government of Ontario, Ontario Weeds:Field Horsetail, https://www.ontario.ca/document/weed-identification-guide-ontario-crops/field-horsetail
- Island Nature, Ancient Horsetails, https://islandnature.ca/2010/04/ancient-horsetails/
- Purdue University, The Ancient Horsetail, https://ag.purdue.edu/btny/purdueweedscience/wp-content/uploads/2021/01/WS-29-W.pdf
- Sierra Club BC, Horsetail, https://sierraclub.bc.ca/horsetail/
- Squamish Chief, The horrors of Horsetail, https://www.squamishchief.com/opinion/the-horrors-of-horsetail-3332392
- Terralink Horticulture, Horsetail, https://www.tlhort.com/images/files/docs/ta_81_weed_bulletin_horsetail.pdf
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