Laidback Gardener Tip of the Day

How to Really Control Horsetail

20150803BIf I had an easy solution for controlling common horsetail (Equisetum arvense), I’d be a rich man But unfortunately this plant is very difficult to eradicate. And to make things worse, it will grow in just about any kind of soil, be it rich or poor, loam, clay or sand, wet or dry.

Do note that horsetail is less likely to become established in dry soils. You see, its wind-blown spores will only germinate under moist conditions. However, once the plant is established, it will readily tolerate dry conditions, although it will grow more slowly under dry conditions than in moist ones. Typically the home gardener accidentally carries a section of rhizome from a moister setting to a drier one, sometimes in soil purchased from a nursery, leading to a new infestation.

In a garden watered regularly for the benefit of other plants, horsetail will be very much at ease and will spread rapidly.

Cultivating Makes Things Worse

20150803CCultivating or hoeing to control horsetail simply doesn’t work. The more you cultivate, the more it spreads, because cultivating slices the plant’s rhizomes into sections and each tiny section of cut rhizome left in the ground will produce a new plant. And cultivation also spreads horsetail tubers, the little “bulbs” produced on its rhizomes, tubers that only produce new plants when they are detached from the rhizome… which is exactly what cultivating does.

Another reason that cultivating doesn’t work is that horsetail tubers tend to be produced deep in the ground, up to 5 feet (150 cm) down, well out of range of cultivation tools!

If you ever decide you do want to try to control horsetail by cultivating the soil, at least make sure you clean your tools before using them in another area, otherwise you risk spreading sections of rhizomes or tubers by accident. The rototiller can be the horsetail-haters worst enemy on this level: not only does it slice the rhizomes into numerous small pieces and spread them hither and yon, but some almost always stick to the blades, transporting them to the next section of garden. A rototiller really needs a good cleaning after each use!

Herbicides

20150803DMost non-selective chemical herbicides available to home gardeners (Roundup is the best known) are simply not effective against horsetail: it just doesn’t absorb them. Lawn herbicides (selective herbicides) are  no better: they’re designed to kill broad-leaved weeds… and few weeds have narrower leaves than horsetail!

One type of biological herbicide, though, is fairly efficient. Vinegar-based herbicides such as Ecoclear or Weed B Gone will effectively kill horsetail foliage, but not its rhizomes. You therefore have reapply them when the plant regenerates from underground, so they will require a bit of followup.

Note that It is difficult to use herbicides, even biological ones, in a  flower or vegetable garden without also accidentally killing desirable plants nearby.

Liming the Soil

The belief that you can control horsetail by adding lime to the soil to render it more alkaline is simply a horticultural myth. Horsetail grows just fine in alkaline soils. Look here for more info.

No Sun, No Horsetail!

You can however eliminate horsetail by preventing it from carrying out photosynthesis. In other words, by cutting off its only supply of energy: sunlight. If you keep its leaves from being exposed to the sun, the plant will quickly stop spreading and will eventually exhaust itself and die.

20150803EOne method of cutting off the sunlight is to cover the infested section with a black tarp. (You can find this kind of tarp in any hardware store.) You have to leave it in place for 24 months to completely exhaust horsetail: it you remove it after only 12 months, there is usually a bit of regrowth. This method is only really practical when you’ve decided to start from scratch. It’s very difficult to use in an established garden with living plants (perennials, shrubs, etc.).

20150803FOne method you can use in an established garden is to simply cut the sterile stems (green stems) to the ground whenever you seen them. Unlike cultivating, which spreads the rhizomes, this causes them to weaken, as you’ll be preventing the plant from carrying out photosynthesis. Start early in the season and re-cut each time the plant regrows… and it will. By repeating each time a new shoot surfaces, the plant will eventually die. However, this method takes some effort: you may need to cut horsetail back 5 or 6 times the first year… and some stalks may still come back in year 2 and should be cut as well.

Or try densely planting with taller plants: tall ferns, big perennials or thick shrubs, anything that will cut off the sun. Horsetail does best in full sun to partial shade. It weakens in deep shade. By creating dense shade, you’ll be ensuring that it will eventually disappear. It may take 2 or 3 years to get total control… but right from the start, taller plants will pretty much hide the horsetail from view.

The Dig and Sift Method

20150803GIn this technique, dig up all the horsetail plants in the sector, putting their rhizomes in the trash (the foliage can go into the compost). Now, empty the bed of soil to a depth to 1 foot (30 cm) and run it through a soil sifter (easily made from a wooden frame covered with ¼ inch (6.4 mm) wire mesh) before putting it back, removing all the rhizomes you find. Of course, some tubers may be left in the soil and manage to sprout, forming young plants. However, if you pull these out within a few weeks, they won’t have time to produce rhizomes and you’ll be able to stop a new colony from forming.

Obviously, this method is most practical for localized infestations. It will be hard to carry out on a large scale.

The Laidback Gardener Method

20150803H
Horsetail mingling with forest plants in the Reford Gardens: just beautiful!

I decided years ago I was no longer going to fight horsetail. I reasoned it was not stealing minerals from my plants (horsetail is not a heavy feeder) and, with its sparse foliage, it lets most of the sunlight through, so my plants still get their share of sun. And unlike dense growing weedy plants such as goutweed (Aegopodium podagraria), it rarely seems to crowd out desirable plants, just to blend in among them. To be honest, I find horsetail attractive. With its beautiful feathery foliage, it can give an attractive misty look to your landscape. If you can learn to accept horsetail as an ornamental, that will save you all the effort of trying to get rid of it.

Oddly enough, once I had decided to accept horsetail as a friend, it began to slowly disappear from my gardens. As they matured and became fuller, denser and shadier, there was no longer any room for horsetail.

Sometimes (and even often), tolerance is simply the easiest way to go… and it’s certainly the most laidback!

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

14 comments on “How to Really Control Horsetail

  1. Pingback: Another Garden Myth to Explode: Lime Won’t Control Horsetail | Laidback Gardener

  2. My horsetail my mom has looks different and by no means is it pretty! Do different varieties work different and or can your method work for all horsetail varieties?

    • Yes, there are several species of horsetail, but they all grow in essentially the same way, just in slightly different environments. As a result, the same treatment will work.

  3. Judith Sterling

    I found your article enlightening to accept the horse tail weed as an ornamental addition to my garden. All the other methods are intense labor or highly toxic or both. What companion plants would you suggest planting that will tame the horse tail?

    • Any taller plant that creates dense shade will eventually push horsetails out: shrubs, taller perennials, etc. Hostas, geranium macrorhiza and others that have really thick foliage are good choices.

  4. Thank you so very much for this informative article.
    I think I’m going to go with your final suggestion and just consider this weed to be an ornamental and a dear friend.

    Been trying to kill the crap for last 5 years and haven’t had any luck.

  5. You can use horsetail as a pesticide because it’s very high in silica. You need to process it in water, boil for 20-30 minutes and strain. The boiling kills the parts that will reseed. But you can make a spray from it and safely use it on plants. I first looked it up after researching diatomaceous earth but didn’t trust that mining it would do a lot of environmental damage to extract it. Then I remembered it was eaten by First Nations people and is high in silica. This is brilliant! So instead I’ll use horsetail to protect my plants!

  6. lesperance1Kim

    I read in one of the links that WD-40 kills Horse Tail, so I tried it. I sprayed the weed really good and made sure it was covered completely with a good coat of WD-40….and IT WORKED!
    I kept an eye on it for a few days and noticed it was starting to wither. After about 4 days it was dead…that was about 4 weeks ago and still no horse tail.
    We were fighting with this weed for 3 years by covering it with a very thick black poly, double layered. If there is a slight opening where light could get in than that’s were the weed would come through and between landscape blocks.
    So yes, please try WD-40 it worked for me and no more horse tail this summer!

    • Just a word of warning: WD-40 is essentially petroleum oil, a serious environmental contaminant, so if it ends up in the soil, it will be like creating your own localized oil spill. It’s harmful to both plants and soil microbes and can create a zone where nothing will grow. Note too that the manufacturer of WD-40 does not recommend this use. Also, it won’t kill the roots, so the the plant will grow back.

      • lesperance1

        Thanks for the feedback.
        It’s been about 2 months now and no horsetail.
        I’m not concerned about the oil contamination because you don’t use that much spray….just enough to coat the plant.
        I’ll have to wait until next year to see if it comes back.

  7. Langdon Plank

    After the gardener, my wife, passed away I have removed all growth in the back yard, and discovered we had about 60
    plants of Horsetail, that had started around 2011. Forty hours of research showed no chemical available in the U.S.
    kills Horsetail with one application. In Mar 2021, a neighbor sprayed a 10′ X 12′ area of Horsetail with a mixture of chemicals made in a prison around 1978. Two weeks later the weeds went from green to brown. In early August 2021,
    I broke the stems of the rest of the Horsetails and gave a good spray. Two weeks later all the Horsetails are brown and
    flat on the ground. You think those 40 year old chemicals could kill those 10 year old Horsetails with one application?
    The backyard was completely covered with 6 Mil black tarp in April 2021 keeping out the early spring rains. Seamed
    areas allowed the Horsetail to grow through. The large 10′ by 12′ area is still all dead. except 3 small growths at the
    edge of the shed’s concrete base. They were resprayed. I’m ready to recover the whole back yard with new 6 Mil black
    plastic–double layers over the Horsetail area–with no seams and will tape the plastic on every wall a foot above the ground, to make it as waterproof and sun proof as possible. Then will cover the entire backyard with 2″ med red lava
    rocks. Do you have any suggestions to this plan?

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