Growing Cotton Grass

Credit: Richard Hebda

Most gardeners know only the familiar show-offs of the wetland and pond gardening world. Brightly hued water lilies and pond lilies grace the pages of many a garden plant book enticing the would-be enthusiast. Pond lilies (Nuphar) and water lilies (Nymphaea) are part of British Columbia’s native flora too. But we also have another attractive and very different group of native wetland and pond plants, the tundra- and bog-dwelling cotton grasses (Eriophorum). Go off the well-trodden dry paths of southern B.C. and enter a boggy wetland or northern mountain pond and you can’t miss the cottony masses waving on thin green stalks. Cotton grasses grow as perennial herbs from tough underground rhizomes. These root-stems proliferate widely just under the surface of the mud, often forming large colonies. Green shoots rise stiffly from the rhizomes and bear narrow leaves at the base and partway along the stem. The upper leaves consist of a sheath that wraps around the stalk and a narrow, grass-like blade that stands away from it. In narrow-leaved cotton grass (Eriophorum angustifolium) several flowerheads erupt among narrow leaf-like bracts from the top of a stem that is 20 to 80 cm (8 to 20 in.) tall. Flower stalk and head may reach a combined length of 8 cm (3 in.). The flower stalks at first are erect, but with age, as the flowerhead develops its cotton-like form, the stalklets droop gracefully. Individual flowers occur at the inside base of brownish scales. Instead of bearing colourful petals or sepals, cotton grasses have long, white- to cinnamon-coloured bristles … the cotton of cotton grass. Florets bear a single ovary with three stigmas and three anthers. The tiny mature fruits, called achenes, are small, brown and somewhat three-angled. They are surrounded by the bristles, which help disperse them on the wind. Several species, such as Chamisso’s cotton grass (Eriophorum chamissonis), have only a single erect flowerhead at the top of the stalk. Its bristles are a delightful tawny brown. Several species of cotton grass occur throughout British Columbia. Of these, narrow-leaved cotton grass is widely encountered in open acidic wetlands, especially in northern muskeg, and at the edge of ponds and slow-flowing streams. It tolerates a range of climatic conditions from lowlands to high elevations and well into the northlands, also ranging across northern Canada and as far south as New Mexico. Chamisso’s cotton grass also occurs widely in B.C., especially along the coast. It favours bogs right around the northern hemisphere. To grow cotton grasses you need a wet and acid site. Obtain plants from a specialist nursery. Alternatively, rooted shoots can be carefully removed in spring through summer with a small amount of enclosing peat from boggy sites and transplanted with little delay into a suitable site. Do so only from places that are going to be destroyed or where disturbance has exposed plant roots. A shallow pool with a peaty substrate makes the best site. Cotton grass will also thrive in a 1-gallon or larger pot, with acid, peat-based soil. Place the pot at the edge of your pond so that the pot surface is about 10 cm (4 in.) below the water surface. Every year or two treat the soil surface with acid-based fertilizer or refresh the peat. For several years I kept a cotton grass plant growing happily in a small bucket of peat, the surface covered in live peat moss (Sphagnum). All I did was make sure the bucket remained full of rainwater or naturally acid water from bog ditches. Cotton grass, despite being obviously visible in the wild, has been little used by First Nations in British Columbia. In the northwest boreal forest, the leaves were eaten, the white base of the shoot being considered especially tender. In Europe the downy bristles were stuffed into pillows and sometimes used as “Arctic wool,” a poor substitute for cotton. Candle and lamp wicks were also fashioned from the bristles. At one time northerners used the leaves and roots as a diarrhea medicine. So, if you are a bit adventurous, go beyond traditional pond plants and try one of our hardy cotton grasses. Once you get a little patch of acid wetland going, you might even be tempted to think about a bog garden, and that may lead to a fascinating set of possibilities. The following plants are hardy to the zone number indicated: • Eriophorum angustifolium (narrow-leaved cotton grass) – zone 0 • Eriophorum chamissonis (Chamisso’s cotton grass) – zone 0 An expert on native plants, Richard Hebda is curator of Botany and Earth History at the Royal British Columbia Museum in Victoria.