Jurassic Park weeds-Horsetail in the garden
by Mary Robson
WSU Extension Agent
Field horsetails, Equisetum arvense, named for their upright brushy shape, are among the most troublesome, invasive, and downright maddening of weeds in the Pacific Northwest.
These are ancient plants, originating millions of years ago when they, with ferns, dominated the landscape. Horsetails once grew to tree-size, a scary thought indeed for people trying now to keep them out of rockeries, vegetable gardens, and shrub plantings.
Their prominence in the landscape is now reduced, but the shrunken remainders of former plants present enough problems!
The toughness of this plant can't be overstated. Horsetail was the first vascular plant to return after the Mt. St. Helens eruption, and it covers the ground near the site of the old Asarco plant in Tacoma. Bad soil and poor growing conditions just don't bother it.
The high percentage of silica-actually silicon dioxide-in the plant made it useful as a pot-scrubber. They were also used as an abrasive for polishing wooden tools.
One type, the Giant horsetail (Equistetum telmatiea) was a favored spring vegetable for native dwellers along the Coast, though they can be poisonous to livestock and humans if eaten in large quantities.
Horsetails, like ferns, reproduce from spores rather than from seeds. The earliest spring growth is the "fertile stems," which produce no foliage, only orange-colored spores that blow around and start new horsetail plants.
Also, the horsetail root system creeps underground, sending dark woolly-brown roots for long distances. Tubers borne on the roots help establish new plants and provide horsetails with perennial vigor.
They spread from garden to garden, suddenly popping up from underground, from a few inches below the surface to six feet down and deeper. After the spore-bearing stems in very early spring, the plant will send up the familiar green shoots with jointed branches and slender needlelike leaves.
All members of the Equisetum family grow well in damp or poorly-drained areas, but they will also colonize drier soil.
So what's a gardener to do? The toughness of the plant and the fact that it moves into gardens from other infested areas makes this one of the most difficult weeds to deal with. Digging it out and pulling it will help, but a plant millions of years old is clearly going to outlive all of us.
In a vegetable garden, keep it hoed down constantly. No chemicals are registered for use in vegetable areas. Hoeing and digging will weaken the plant slightly, and will get it out of sight.
However, constant efforts must be used on the plants. Keep pulling to prevent the week from restocking its roots and tubers with strength and gained by photosynthesis from the green growths. There's a certain vicious pleasure to pulling these out, even it's not a total solution.
Horsetails in lawns are generally easy to manage. The constant mowing keeps the plant down. They aren't gone; they are just mowed to be less visible.
Field horsetail won't respond to most common herbicides during the active growth season. Spraying it with glyphosate (Round-up and other brand names), 2, 4-D, or triclopyr just doesn't work. Spreading a weed barrier cloth (various geo-textiles are sold) can reduce the infestation some, but remove all growth before spreading the material. Put a mulch on top.
Winter control, surprisingly, does have some effect. After the plants have died completely down, in late December or January, apply a preemergent herbicide called dichlorbenil (sold as Casoron and under other trade names) can help. Mulch over the herbicide after it's placed.
Be very careful with this product. Dichlorbenil is easy to overapply and can damage valuable plants. It cannot be used around newly-planted shrubs or trees. Woody plants have to be established for at least six months before using dichlorbenil. It's not safe to use over new flower or bulb plantings or over vegetables.
In an established shrub border, dichlorbenil applied before the weed comes up in early spring, and with a mulch laid over the herbicide, can help to reduce the infestation.
In summary, be patient and persistent about horsetail control. If all neighbors in an area, particularly where gardens touch each other with fence separation, will control horsetail simultaneously, the effort is more effective.
These plants are a worldwide weed problem, so we can at least take comfort in having millions of other people attempting to handle a weed that is millions of years old.
Beginner's guide to compost
"Backyard Composting in the 1990s" is the name of a new bulletin that tells you all you could possibly need to know about the art of composting.
The publication covers starting a compost pile, speeding up the process, quality improvement, compost use and answers to health and safety questions.
The cost is $2, which includes shipping and handling. Make checks payable to Cooperative Extension Publication. Request publication #EB1784, Backyard Compost-ing in the 1990s.
Mail orders to: Bulletin Office, Cooper Publications Building, Dept. WD-C, WSU, Pullman, WA 99164-5912.
Washington State University Cooperative Extension Master Gardeners will answer gardening questions from 9-4 -Monday-Thursday, and 10-2 Fridays. Call 338-2400.