The correct common name for it is ‘horsetail’, although it is often wrongly called ‘marestail’. Either might seem to be appropriate, for equisetum comes from two Latin words, equus … meaning ‘horse’ … and saeta … ‘bristle’; and arvense is another Latin word, meaning ‘in the fields’, from which you will gather that equisetum arvense is a plant which likes open ground, rather than woodland, and thrives in cultivated ground. If it would confine itself to the fields then gardeners would be truly grateful. But equisetum arvense is always happy to accept an invitation to enter gardens even though it is not welcome there.
Let’s first of all deal with the matter of whether its common name is properly horsetail or marestail. Many people, including myself, use either name indiscriminately: but there is an entirely different plant … Hippuris vulgaris … which is also known by the common name of marestail, a freshwater plant, no less; and equisetum arvense really should be called horsetail. So what is it about horsetail which makes it a particularly unwelcome intruder in any garden and makes it doubly unwelcome in a lawn or a rock garden?
I am never averse to quoting definitions which sum up a plant better than any words of mine can; and so I turn to Lawns, Weeds and Ground Cover, by David Pyecraft, first published by the Royal Horticultural Society in 1980, for this succinct description: “Field horsetail is a perennial leafless plant with dark, wide-spreading rhizomes which may penetrate 6 feet or more into the soil.” And, given that a rhizome is a continuously growing horizontal underground stem which puts out side shoots and random roots at intervals, the gardener’s problem with horsetail is easily understood; it is very difficult to eradicate the plant from any area which it decides to colonise.
Trying to pull the roots out by grasping the shoots that appear above the ground is usually futile; the shoots break off, leaving much of the root system intact. Trying to dig the roots out is usually equally futile; while enthusiastic digging and careful riddling of the dug soil will remove much of the root system, the deepest, hardest-to-reach roots all-too-often survive the process, allowing the plant to re-establish itself. Covering over the entire area where the plant has thrown up surface shoots … a successful tactic with many weeds … is a waste of time, for horsetail simply spreads underground (even under concrete!) pretty much as far as it needs to go; and it is a perennial, non-flowering plant which does not need to be pollenated and so produce seed in order to thrive, surviving by virtue of its ever-extending root system. Its transfer from an established area to new territory is most often achieved by the gardener, who inadvertently imports stem fragments in composts or manures.
Infestations of horsetail can be treated with a systemic weedkiller … that is, one which is ingested by a plant’s foliage and then moves through the stems and roots. The best are those that contain a chemical called glysophate; but do remember that, although systemic weedkillers are harmless if the spray falls on soil, they are absorbed by the foliage of most plants, so careful application is necessary and they cannot be used on areas like lawns. When I moved into my house many years ago, it was possible to buy ‘neat’ glysophate and I killed off an infestation of horsetail by injecting a concentrated solution of the chemical into every shoot I could find. It was time-consuming work … but it certainly was effective!