Field horsetail

About

Field horsetail is an ancient, flowerless native plant that spreads by spores and very deep rhizomes. It is hard to eradicate from wet garden soil and is poisonous to horses and other livestock.

Also called common horsetail, horsetail, western horsetail

How to identify it

Look for

In early spring, pale tan, unbranched fertile stems 4 to 12 inches tall appear, each topped with a cone that sheds spores. Soon after, green sterile stems up to about 2 feet grow, with rings of thin needle-like branches at each joint, making them look like little bottle brushes. Stems are hollow, jointed and gritty with silica, with small dark teeth at each joint.

Look-alikes

Scouring rush (Equisetum hyemale) has taller, stiff green stems with no whorled branches.

Where it grows

Wet, poorly drained or sandy and gravelly soils in gardens, landscapes, ditches, roadsides and pastures; common in the Pacific Northwest.

When

Fertile stems come up in mid-spring and die after shedding spores; green stems follow in late spring and last until frost.

How it spreads

By spores and by creeping rhizomes and small tubers that can run 6 feet deep or more and regrow from fragments.

Most common in

What to do, gentlest first

Start at the top. Weed killers are a last step; always read and follow the label.

1. Improve drainage Prevent

   Fix leaks, cut back on watering and improve drainage; horsetail dislikes well-drained, shady spots, and raising acidic soil pH also discourages it.

2. Pull tops again and again By hand

   Pull or cut off all stems about 2 weeks after each flush comes up and dig out rhizomes and tubers where you can. It can take several years of steady pulling.

3. Plastic or fabric, not bark Barrier

   Use black plastic, landscape fabric or roofing paper covered with soil or mulch; organic mulch alone does not stop it.

   Shoots may push up again when the cover comes off.

4. Fatty-acid (soap) burndown Organic spray

   Ammonium salts of fatty acids can burn back top growth, but the waxy stems shed sprays and the rhizomes survive, so repeat often.

   Read and follow the label.

5. Selective or pre-emergent herbicide Conventional spray

   Lawn products with 2,4-D, dicamba, MCPP, triclopyr or sulfentrazone give partial control; dichlobenil granules applied in winter or early spring are used in landscape beds.

   Read and follow the label; many lawn and brush herbicides also kill garden plants. Never spray near water unless the product is labeled for it.

Uses, wildlife and pets

For wildlife

It gives cover and some food to small mammals.

Pets

Toxic to horses (ASPCA lists field horsetail as toxic to horses); it breaks down vitamin B1 and can cause weakness, staggering and even death in livestock. Not listed by the ASPCA for dogs or cats.