A clump of scouring rush stands out in a bed of dwarf horsetail (Equisetum scirpoides) that stands only about 8 in (20.3 cm) tall.
This is the scouring rush's spore-producing strobilus. Click to download a large version of this image for a closer look.
Common scouring rush is a spreading, reed-like perennial to 3 ft (0.9 m) tall. The evergreen stems are cylindrical, about 1/3 in (0.8 cm) in diameter, jointed, hollow, usually unbranched, and have rough longitudinal ridges. The tiny leaves are joined together around the stem, forming a narrow black-green band or sheath at each joint. Like other Pteridophytes (ferns and their relatives), scouring rush does not produce flowers or seeds. Instead it develops a brown, cone-shaped, spore-producing strobilus at the tip of fertile stems, which are shorter than the infertile stems. The spores themselves are microscopic.
There are about 25 species of horsetails or scouring rushes occurring throughout the world except in Australasia. Common scouring rush occurs in wet places, including pond margins, swamps, floodplains and ditches, in Eurasia and North America. It sometimes forms dense stands along bogs or marshes in northern US and Europe.
Culture Light: Full sun to filtered sun. Moisture: Scouring rush can tolerate prolonged wet conditions, but should not be totally submerged nor allowed to dry out. Hardiness: USDA Zones 3 - 11. Propagation: Scouring rush spreads by shallow rhizomes (underground stems) and is easily propagated by dividing the clumps and immediately replanting the rooted individual plants.
Scouring rush is often grown in Japanese-style gardens, at the edge of ponds and in the margins of ornamental water gardens. It can be invasive if conditions are favorable, so, unless you want a large, spreading stand of it, it is advisable to maintain scouring rush in containers sunk in the ground with the lip just barely above ground level. However, a dense stand of scouring rush along the margin of an ornamental pool can be very attractive and will exclude weeds.
The scouring rushes are ancient plants that were dominant in the latter part of the Paleozoic Era (360-250 million years ago). There were many genera and species, some as large as trees. Scouring rushes and their relatives were especially dominant plants in swampy areas during the Carboniferous Period (360-290 million years ago) of the Paleozoic Era, and were abundant among the deposits of vegetation that later were transformed into coal. Since then they all have gone extinct except for one genus with a couple dozen species, living relics from an age millions of years before the dinosaurs existed! Scouring rush has been used to scour cooking utensils, and is still harvested commercially in northern Mexico for polishing fine furniture.
WARNING Scouring rush contains large amounts of sharp silica crystal making it painful, if not actually life-threatening, if ingested. It has been reported to sicken cattle.