Keep Horsetails in Containers and Do This

Q. I have numerous horsetails planted in pots in a dry riverbed to keep them from spreading into my landscape. One of these plants appears to be dying and I’m thinking that others will in the future. Is it because they are becoming root bound in the pots? Can they be contained if I plant them in the ground instead?

A.  Horsetails, or Equisetum as it might be called, can become root bound the same as any plant grown in a container. All plants grown in containers must be replanted every few years when they become large. Plants that grow in clumps, like horsetail, are reduced in size through “plant division”. But I doubt this is the problem.

Loves Wet Soil

            Horsetail, unlike most landscape plants, loves wet soils that drain poorly. They grow best when planted near a pond and keeping the soil wet rather than along a dry riverbed. Their native habitat is in marshes and wetlands that are constantly wet. I think the problem is most likely dry soil so look closely at your irrigation practices. In any case, keeping the soil wet should be your first consideration if they are not growing well.

Double Potting

            Do not plant horsetail directly in the landscape. These plants are notorious, aggressive invaders. They will take over a landscape if it’s wet and controlling their spread is very difficult once they are turned loose.Sometimes this is called pot in pot container growing.

            Growing them in containers placed in the landscape requires double potting them; the container with the plant is placed inside a second container permanently installed in the ground. This second container has a 2 to 3 inch layer of rock at the bottom to prevent the containers from lodging.

            You must, must, must twist the inside container in a circle every two or three months to prevent roots or rhizomes from entering landscape through the outside container. If you don’t, the roots will grow through both containers and the plants will establish themselves in the landscape and spread.

            When dividing a bunching perennial like horsetail, remove it from the container and cut the rhizomes that connect bunches together into a single clump. This results in two or three smaller clumps. Replant one of the smaller bunches in the container with fresh soil and reestablish the irrigation. It will become a bunch again, that needs to be divided, in 3 to 4 years.