Nothing marks the passing of eons like fossils, and scouring rushes may be the oldest living land fossils. Scouring rushes and horsetails belong to the botanical plant genus Equisetum. Many readers may recall their personal heroic garden battles with horsetails and for good reason. Plants in the genus Equisetum have survived most of the major global extinction events and are among the toughest organisms on earth.
The naked stalks of tall scouring rush (Equisetum hyemale) stand bamboo-like in masses, often among shrub stems. These evergreen shoots arise from a vigorous underground rhizome (root-stem) system, parts of which occur near the surface and other portions of which may be metres deep in the soil. These firm black structures bear numerous short rootlets at the nodes and sometimes water chestnut–like tubers. The stalks are hollow and unbranched, rising stiffly 20 to 150 cm (8 to 60 in.) tall. They bend easily between the widely separated nodes and you can split the stems open by running your fingernails lengthwise. The stalk surface has rough vertical ridges distributed between the firm nodes. There are leaves at the nodes but you have to squint hard to see them, for they have fused and shrunk into a blackish band, at the top of which are the tiny tooth-like leaf tips.
Scouring rush is a most primitive plant; that is, it has no flowers and does not reproduce by seeds. Like ferns it reproduces by spores formed in sacs grouped into tiny soft cones at the tops of the stalks. The spores spread by air and when they land on a moist surface, they develop into inconspicuous filmy plantlets. Male sperm swim from the male reproductive structures to fertilize eggs on the plantlets where a mature plant develops.
Scouring rush occurs throughout B.C., even in the cold northlands. Globally it ranges around the Northern Hemisphere and in North America as far south as California and Florida and eastward into Labrador and Newfoundland.
The habitat includes moist sites such as stream banks, flood plains and wetlands from lowland to mid elevations. The edge of swampy thickets is a good place to look for it. Tall scouring rush often favours partial to full summer shade, though in the Interior of British Columbia it thrives on sandbars in full sun. Scouring rush colonizes roadsides, railway embankments and old fields, too. On the B.C. coast, you may encounter another very tall (to 3 m/9 ft.) evergreen species, giant horsetail (Equisetum telmateia), which bears branches at the nodes. Common horsetail (Equisetum arvense) is also branched and grows just about everywhere. It is the bane of many a gardener as its deep-seated rhizomes are next to impossible to remove. No matter how hard you work at it there seem to be new recruits waiting to take the place of their fallen comrades.
For the garden, tall scouring rush is best propagated from rhizome divisions removed from the soil with at least one stalk attached. It may also be available in pots from nurseries specializing in wetland and aquatic plants. Scouring rush is widely used as a potted accent subject or pond and wetland plant, also contained in a pot. Scouring rush rhizomes have the ability to spread, though not as invasively as those of common horsetail. If you have a large pond, then you can let it roam freely, especially among shrubs. Transplanted clumps may take a year or two to become established. Almost any moist soil will suffice, but a somewhat loose, gritty, moist soil with abundant organic matter is ideal.
As the common name suggests, the ridged stalks are rough, because they contain silica. First Nations people used the stalks to polish (sand) wooden objects such as canoes, dishes and arrow shafts. Some people used the dark rhizomes to decorate woven baskets. You can use the stalks when camping in the bush to scour out your frying pan and pots.
Apparently, the green shoots are used by some people as an asparagus–like vegetable, and medicinally as a diuretic and for many other purposes. HOWEVER CAUTION IS STRONGLY ADVISED!! Scouring rush contains an enzyme that interferes with vitamin B in the body. Use only small quantities or cook or dry the stems and roots in the sun to destroy the enzyme.
Scouring rushes have been around for a long time, since the Paleozoic Era more than 350 million years ago, making them perhaps the oldest living fossil on land. Long before the appearance of dinosaurs in the Mesozoic Era, gigantic woody relatives of our tall scouring rush, called Calamites formed leafy forest stands up to 20 m (66 ft.) tall during the Carboniferous (Coal) Period 300-360 million years ago, and their fossils are well-known the world over. By the end of the Lower Permian Period, (270 million years ago) herbaceous Equisetum species replaced those woody horsetail relatives.
Honour our ancient primitive plants with a pot of tall scouring rush in your garden. It provides a fascinating, simple, structural form to use in moist, dull corners. And as you struggle to eradicate common horsetail remember deep time is on its side; it will undoubtedly outlast the human species and prosper long into the future.