781 Arundo donaxCommon Names: giant reed, carrizo Family: Poaceae (grass Family)
Giant reed is a huge and robust bamboo-like grass with large, spreading clumps of thick culms to 20 ft (6.1 m) tall. (A culm is the above-ground stem of a grass or sedge plant.) The numerous leaves are about 2 in (5 cm) wide and 12-24 in (30.5-61 cm) long, and arranged conspicuously in two opposing ranks on the culms. The leaves look like those of a corn plant. Their margins are sharp to the touch and can cut careless hands. The inflorescence, appearing in late summer, is a 1-2 ft (0.3-0.6 m) long purplish (aging to silver) plume that stands above the foliage. Giant reed spreads from thick, knobby rhizomes. The foliage dries to light brown in the winter and rattles in the wind. Striped giant reed (A. donax var. versicolor, also known as cv. 'Variegata', has leaves with bold white stripes, and is a smaller plant, to 8 ft (2.4 m) tall. The cultivar, 'Macrophylla' has larger leaves, to 3 in (7.6 cm) wide, that are grayish or bluish green.
Native to the Mediterranean region, giant reed has been widely introduced and is now common in many parts of the world, including the southern U.S. from California to Florida and northward on the East Coast to Maryland. It can be found growing on river banks and in ditches. Giant reed often is planted to control erosion on wet slopes and canal banks. It can be an invasive weed in tropical climates, clogging irrigation ditches and displacing native species in natural wetlands. Giant reed is not invasive in temperate regions.
CultureLight: Full sun. Moisture: Giant reed grows best and gets largest with lots of water during the growing season. It thrives in soils that stay moist, and can even tolerate occasional standing water. Unlike most reeds, however, giant reed also does well in average garden soils, where it will not get as large nor spread as aggressively. It even tolerates drought. Hardiness: USDA Zones 6 - 11. Giant reed gets largest in frost-free climates where it grows to 20 ft (6.1 m) and stays evergreen. It dies to the ground in frosty areas, and may not flower, but it comes back in spring to get 10-12 ft (3-3.7 m) tall in a single growing season. Var. versicolor and the variegated cultivars are hardy only to zone 8. Propagation: Giant reed can be propagated by rooting sections of the stem in water; pot up when roots have developed and keep moist for a few months before planting out. Giant reed is easy to propagate by dividing off pieces of the rhizome in spring.
Giant reed is grown as an ornamental for the striking appearance of its large two-ranked leaves that arch gracefully from stout, sometimes purplish stems, and for the huge feather-like panicles of purplish flowers. Not counting the bamboos, this is the largest and tallest ornamental grass, and the tallest grass that can be grown outside the tropics. It is best used as a bold and attention-grabbing accent near water or in the background of large gardens. Use giant reed freely in areas with cold winters, but beware of its aggressive invasiveness and large size in zones 9-11. The large, thick and fluffy flower plumes are excellent in dried arrangements. Cut the plants back in late winter and use the old stems as supports in the vegetable garden.
Giant reed is widely planted in wet soils to control erosion. The reeds in woodwind musical instruments are made from the split stems of giant reed, and organ pipes formerly were made from sections of the stem. The durable stems have been woven together to make wattle for use as walls, fences and roofs for thousands of years.
Giant reed is invasive, and can crowd out native wetland plants in tropical and subtropical climates. The California Exotic Pest Plant Council lists giant reed as one of the most invasive wildland pest plants in southern California wetlands. Except in its natural range, gardeners in Zones 9-11 should not plant giant reed.
Steve Christman 8/27/00; updated 10/16/03