Although common or field horsetail is not included on lists as an invasive species, it is a problem species. Pacific Northwest Invasive Plant Council does list giant horsetail, Equisetum telmateia, as invasive in Oregon. Horsetail is of concern because of its aggressive root system, which consists of rhizomes and tubers, that can spread 2-3 feet wide and 6 feet down into the soil. It also produces spores which are carried in the air. For these reasons, horsetail is one of the most difficult plants to get rid of and should be prevented from becoming established.

Although native, it is native to most of North America and Europe. When found in pastures, it is toxic to livestock and other animals, and when it finds its way to waterways, it can impede waterflow.

If you choose to try and control horsetail, there are several things you can do.

Hand remove horsetail about 2 weeks after it emerges from the soil. The helps to deplete food reserves in the rhizomes. Unfortunately, it will take several years of pulling, but will provide effective control.

Make sure the soil is well-draining. Add organic matter or compost and do not use a mulch or other groundcovers to encourage retention of water.

Horsetail is less likely to establish in the shade. You might want to think about plants to make the area shady. Closely spaced shrubs and trees will not allow as much direct light to penetrate and help to decrease the likelihood of horsetail.

Research shows that making the soil less acidic by adding lime may help to decrease horsetail from reappearing.

A combination of well-draining soil, shade, and lime can help to reduce the prevalence of horsetail. And be sure to continually survey your yard and make sure to take care of any horsetail that might have sprouted.

If you decide not to try and control horsetail, it will continue to spread and threaten to overwhelm your yard and surrounding areas.

For more information on horsetail:

OSU - Department of Horticulture - Field Horsetail

Equisetum - Horsetail