Horsetail (Equisetum arvense) in a garden - undeterred by mulch
The title of this post is taken from the title of an article in the Squamish Chief newspaper that details the difficulties of living with the plant known as horsetails. "A weed is a plant whose virtues haven't been discovered yet." says Ralph Waldo Emerson. In a reactionary New York Times Magazine piece, entitled Weeds Are Us (http://michaelpollan.com/articles-archive/weeds-are-us/), Michael Pollan humorously describes his conversion from an Emersonian view to weed whacker. Pollan makes the point that not only are weeds plants that interfere with human plans, but they are also plants that have flourished as a result of human activities. Weeds are denizens of disturbed sites like vacant lots, roadsides, gardens, and lawns. As such, weeds are creatures of the Anthropocene, the epoch in which human changes to the earth have become more significant than natural change and an underlying theme of this blog. It is an irony that the subject of this post, horsetails, a weedy success in the Anthropocene, is an ancient plant, often referred to as a living fossil.
Horsetails (Equisetum arvense) climb steps up Queen Anne Hill in Seattle.
The ancestors of horsetails were dominant plants in the Paleozoic Era, more than three hundred million years ago. These plants ranged from understory shrubs to trees that grew up to one hundred feet in height. Today, only a few species of this group survive. But, they're still making an impact. A Google search on horsetails as weeds finds that: "getting rid of horsetail weed is a nightmare"; it is the weed challenge that "will make you feel like throwing away the trowel"; "I'm thinking about giving up gardening"; "this weed is the worst I've ever seen." The BBC even provides a video to assist gardeners in removing this pernicious pest. The success of horsetails in the Anthropocene involves a fascinating, and unusual, life history that reflects its ancient evolution. The horsetails we see above ground arise from nodes along a shoot growing deep underground called a rhizome. This is part of why it's so difficult to eliminate horsetails. Cut down or pull the horsetail plants and the rhizome, which produces tubers where the plant stores energy supplies, will simply send up new shoots in their place. As the rhizome extends underground, it forms a clump of horsetails above it. The general consensus is that horsetails aren't well controlled by the usual weeding techniques such as mulching, black plastic, chemicals, mowing, or pulling. The best solution for gardeners seems to be changing the soil chemistry and drainage. Horsetails prefer more acidic and moist soils.
Horsetail spore-producing strobili (yellowish, no leaves) present in the spring. Notice leaves that are just beginning to appear on adjacent stems.
Rhizomes also produce specialized shoots without leaves in the spring called strobili. The strobili are essentially reproductive organs, producing spores that will scatter to the wind. Strobili of the field horsetail (pictured above) have no leaves and do not carry out photosynthesis. They are produced solely for reproduction and soon die back. The spores themselves are also remarkable. There is a wonderful YouTube video called "The Walk and Jump of Equisetum Spores" (https://www.youtube.com/watch?v=RvC4pOb7MhE) that captures the movement of horsetail spores. In it, you can see that the tiny spores have four "arms" that, in reaction to changes in humidity, spring from a clenched to an extended position. The result is that the spores may jump out of the strobilus, or may walk or jump along on the soil surface. Jumping in the air may also increase the chances of being caught in the breeze and thus further transport. Jumping and walking are quite an adaptation for spreading the spores of this ancient plant!
Despite their interference with garden plans, there is a lot to like about horsetails. They outlasted the dinosaurs, can grown in poor soils, and have been used medically and even to polish metal and wood. The polishing is best accomplished with a particular species of horsetail that is known as rough horsetail or scouring rush. Horsetails in general tend to accumulate silica and rough horsetail stems have silicone-containing ridges that work well for polishing. We have rough horsetails growing in a pot outside (picture below). I find these and other horsetails to be quite attractive. In this case, a weed for one person is a decorative plant for another. And, knowing a little more about the plant may also affect how we see it. There is much to appreciate about the nature we find underfoot - tread lightly.
Stems of rough horsetail (Equisetum hyemale) rising above another plant in a pot. Small greenish-blackish leaves are formed at each node.