The giant fleeceflower (Persicaria polymorpha) is a massive perennial fairly new to the market. It forms a clump so dense that no weed can penetrate it, so it really holds its own in the garden. Its very thick stems are hollow and bamboolike, but its large oval leaves look nothing like the narrow lance-shaped leaves of most bamboos and the two plants are not related. The giant fleece flower blooms all summer, for about 3 months starting in May or June depending on your climate, with large panicles of feathery creamy white flowers. From a distance it looks like a goat’s beard (Aruncus dioicus), but its foliage is very different. By September, blooming will be in decline and the flowers will have taken on a pinkish hue. There is no winter interest and it’s best to cut it back to the ground in late fall.
The flowers of the giant fleeceflower are scented, but their perfume is certainly not flowery. Some people like the smell, others hate it! Fortunately you have to be really close to notice it.
Giant fleeceflower readily reaches 4 feet high by 4 feet in diameter (1.2 m x 1.2 m) in its first year and can eventually reach 8 feet (2.5 m) under good conditions, so it is truly a huge perennial. It tolerates pretty much any kind of soil, but does best rich, fairly moist soil. Well-established plants are fully drought resistant. Flowering is more abundant in sun or partial shade, but it will grow well and flower modestly in the shade. It adapts to most climates, from hardiness zones 3 to 9.
Unlike other knotweeds (genera Persicaria, Polygonum and Fallopia), many of which are highly invasive, giant fleeceflower is not rhizomatous but grows in dense clumps. After several years of culture, however, it may produce an offset or two. Dig them up while they are still young to stop any unwanted expansion. You can use these offsets for propagation purposes, but it is also possible to multiply this plant by cuttings or by division. There appears to be no seed formation on cultivated plants, so no threat it can spread by seed.
Finally, an additional tip: plant lots of spring bulbs at the base of your giant fleeceflower. It’s slow to come up in the spring, so the bulb will have time to flower and begin to turn yellow before big guy’s leaves hide them from view. So you will have lots of flowers in spring and blooms all summer until fall: truly a winning combination!