Ancient Weeds Don’t Give Up Easily

Dino food is still with us

Out, Out Damned Horsetail

This weekend I visited a wonderful older garden with a magnificent berm overlooking Puget Sound. It was good to have such a satisfying vista to admire because looking at the berm made my heart ache. Lovely as the plants were, the entire bed badly needed enrichment and overhauling, which would be a big job. However, the most discouraging thing about it was that almost every inch was covered with fluffy fronds of emerging horsetail. It made me grateful that the owner’s eyesight is failing; the big picture is still delightful but closer views are seriously daunting.

 As gardeners quickly learn, horsetail is one tough plant: Pull it, spray it, do what you will; back it comes, stronger than ever. That’s because it’s a prehistoric survivor, a lingering remnant from the dinosaur days with roots that can delve six feet or more. Sometimes way more. A little flick of the trowel is not going to set it back for a hot minute. The Northwest has been home to quite a few species of Equisetum for millennia, surviving climatic changes that wiped dinosaurs off the map. Tough, enduring, and incredibly deep rooted, it’s small wonder that horsetails pop up in so many gardens.

A Horsetail For Every Garden

The most common form, field rush (Equisetum arvense) is found from wet lowlands to high alpine meadows. Where shade suppresses common horsetail, the same ecological niche is filled by its cousin, wood horsetail (E. sylvaticum). In wetter places, swamp horsetail (E. fluviatile) takes over, sometimes letting meadow horsetail (E. pratense) have a go in swampy fenlands. Non-flowering scouring rush, Equisetum hyemale, is an elegant creature often grown as an ornamental water plant in other parts of the country. In the Northwest, this slim, long-lined creature doesn’t get much respect. Neither does its slimmer cousin, E. variegatum, most often found at sea level.

Most dramatic of all the the giant horsetail, E. telmatiea, which can stretch close to 10 feet tall in preferred sites. As long as the preferred site isn’t your rose bed, this really is a magnificent plant that would look utterly at home in a big tropicalismo border full of bold foliage. Objectively, horsetail truly is a beautiful plant. I once visited a fancy florist shop in New York City where a stunning bowl held architectural, upright spears of “non-flowering scouring rush” and cost $150 (and this was decades ago, when that was still significant money). I thought I could retire rich, but the staff was not interested in buying horsetail from me. Oh well.

Mow Or Cut; Don’t Pull

Stunning or not, few of us welcome horsetail in our own backyards because it does not share well with others and is damnably difficult to remove. Though weekend warriors love to use chemicals on horsetail, even the strongest toxins only wipe out this season’s stalks. Mulching with plastic creates a lovely nursery bed; horsetail loves dank, dark, acid, anaerobic soil. The good news is that mowing is far more effective and environmentally sound. That’s because the best way to get rid of horsetail is to cut, not pull. Pulling a piece of horsetail actually stimulates new growth. Pull one stalk and you scar the root, causing a hydra-head of three or four or five new shoots to take its place. Cut that stalk at ground level, over and over, and you will slowly deplete the roots.

Sometimes horsetail comes in with a load of top soil or even (horrors!) compost-if so, never buy from that supplier again. That’s never good news, but at least you have a fighting chance of getting rid of it, because the shoots will be coming from broken bits of those deep, deep roots. Dig the stalks out whenever you see one and in time you can truly be free of this implacable beauty. It’s important to keep on the task, since horsetail is most vulnerable before it gets well established. The fresh green tops can be put in the compost, where they supply silica and other trace minerals in unusual abundance. However, don’t put even a tiny scrap of horsetail root in the compost or you will be sorry indeed. Bag or burn the roots, which can re-sprout pretty much all year round.

Now What?

If, however, horsetail is well established in your garden or lawn, the only way to get rid of horsetail permanently is to change the conditions it grows in, no small task. Horsetail often grows vigorously on recently cleared land, on home sites built over hardpan or clay, and around underground seeps that provide moisture deep below the soil surface. Sometimes the topsoil is sandy and loose, yet stands of horsetail persist. If you dig down, you’ll discover a layer of hardpan or heavy clay way down under that sand. Horsetail is an indicator plant, telling us loud and clear that somewhere on the scene, hard, heavy soil is lurking. The favored environment for horsetail is dense, damp soil that’s low in oxygen and high in moisture. 

Here in the maritime Northwest, such acid, airless clay soils abound. To make things worse, our native soils also tend to be very low in humus, the organic material that feed soil dwelling microbes. In order to eliminate horsetail, we need to create oxygen rich, nutrient rich, nearly neutral soil with lots of humus. To achieve this, we must do three things:

* Improve drainage to improve oxygen balance.
* Add humus (compost) to improve organic soil content.
* Neutralize your soil at least somewhat (compost again).

Beds Go Up, Paths Go Down

On heavy, retentive soils, excavate all your paths and fill with crushed gravel. By dropping the internal level of the paths even slightly, we can use them like French drains to direct the water off the garden site. The top surface of the path can remain level to the eye and foot, but the trench beneath the surface should drop about 3-4 inches over every 10 feet of run. At the end of the path, make a rain garden, or plant dwarf willows, redtwig dogwoods, and other moisture lovers that thrive in heavy, damp soils.

On heavy soils, it is critical to mound beds rather than excavate them. Digging out clay beds is like making nice little bathtubs in which to drown your innocent, unsuspecting plants. Resist the impulse to dig and go up instead. Mound any infested beds, giving them a positive soil profile of 8-12 inches above grade. Where possible, remove the plants first and improve the bed soil with a blend of fresh topsoil mixed with half the volume of mature compost. Mulch the whole bed with 2-3 inches of compost as well. Where you can’t dig up everything, add 4-6 inches of compost. To avoid smothering established plants, feather the compost so that there is no more than half an inch at the trunk or main stems of your plants.

Know When To Fold ‘Em

Where mounding is not possible (perhaps because of mature trees), spread dolomite lime at the rate suggested on the back of the bag. Next, mulch deeply with compost (2-4 inches), taking care not to smother the crowns of existing plants. Every spring and fall, spray the entire yard with aerobically brewed compost tea to increase microbial life, which improves oxygen levels in soil. Every spring and fall, mulch again with several inches of mature compost, always taking care not to smother existing plants. Do all these things faithfully and each year, your plants will look better and be healthier, and you’ll have less and less horsetail.

Sometimes, however, we have to suck it up and learn to love the horsetail. As a rule, horsetail or scouring rush should not be eradicated along natural streams or in natural bogs and wetlands where it is an important member of the ecological community. In such situations, it helps to interplant with hardy geraniums, or generously scatter seed of Verbena bonariensis, which make lovely seasonal companions for horsetail. If you can’t beat em…