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Monday - July 27, 2009

From: Etna , NH
Region: Northeast
Topic: Invasive Plants
Title: Invasive horsetail in Etna NH
Answered by: Barbara Medford

QUESTION:

I seem to have an increasingly "healthy" supply of Equisetum in ALL of my many gardens over the years .. it is not easy to get all the rhizomes (what is?) is it possible to control it some other way? Could pH have something to do with it?

ANSWER:

There are 10 species of the genus Equisetum native to New Hampshire; we have chosen Equisetum hyemale (scouringrush horsetail) as a representative species to use as an example. It and the rest of the Equisetum genus are very much wetland plants-they tolerate shade, poor drainage, occur in wet places and even standing in water. They are considered very aggressive, which you have already found out.

We felt your question about the pH having something to do with the too-healthy growth of the horsetails was thought-provoking, but we could find no research to support that one way or the other. What we did learn was that it did best in marshy, poor drainage soils, and even standing in water. We don't know what kind of garden you have; if you have a water garden, and started the Equisetum in that water garden without confining it in pots without holes, that is no doubt the source of your problem. If it is growing in your soil, the soil must be very poorly drained, and we are wondering what other plants you have been able to grow there.

Everyone wants a special spray that will just kill the one plant they are interested in eliminating. The Lady Bird Johnson Wildflower Center recommends neither for nor against the use of herbicides. We found two articles that dealt with elimination of this plant. The first is from University of Minnesota Extension Horsetail by Beth Jarvis. Here is an excerpt from that article:

"Horsetails are difficult to eradicate without the use of herbicides. They favor damp, sandy or gravelly, shady places. Depending on where they're growing, improving drainage and fertility and increasing the organic material in the soil along with regular mowing or clean cultivation may make the site less hospitable. Digging the plants out, in all but the smallest sites, could be prohibitively difficult due to the depth and spread of the underground rhizomes."

Another article, from a UK newsgroup, has more herbicide information to add: Re: Horsetail Roots.

Our conclusion from all of this is that you may need to modify the environment in which your garden is growing. In other words, improved drainage, drier, richer, maybe with taller plants to shade out the Equisetum. Cut off the spore-bearing cones before they ripen and spread more spores, but with all those rhizomes under ground, it will be difficult to starve out the plant.