Giant Knotweed (Polygonum sachalinense)

At a glance

Lifecycle: Perennial (hardy)
Exposure: Full sun
Frost limit: −28.9 °C

Cultivation

Succeeds in ordinary garden soil in sun or shade. Hardy to about -25°c. An extremely invasive plant, capable of sending up new shoots at a considerable distance from the main clump. Considered a pest in many areas, if grown in the garden it should be planted within a barrier to contain its roots. Plants seem to be immune to the predations of rabbits. Dioecious, male and female plants must be grown if seed is required.

Propagation

Seed - sow spring in a cold frame. Germination is usually free and easy. When they are large enough to handle, prick the seedlings out into individual pots and plant them out in the summer if they have reached sufficient size. If not, overwinter them in a cold frame and plant them out the following spring after the last expected frosts. Division in spring or autumn. Very easy, larger divisions can be planted out direct into their permanent positions. We have found that it is better to pot up the smaller divisions and grow them on in light shade in a cold frame until they are well established before planting them out in late spring or early summer.

Edible uses

Young shoots in spring - raw or cooked. They have an acid flavour and we find that they are more like a rhubarb substitute. Older stems and shoot tips - cooked. The stems are best peeled. Tasting like a mild version of rhubarb, they have a superior quality with a hint of lemon in the flavour. Seed - cooked. The seed can be ground into a powder and used as a thickener and flavouring in soups etc, or as an extender in flour. It is rather small and fiddly to utilize.

Material uses

A potential source of biomass. Plants are very vigorous and could be grown as a ground cover.

Giant Knotweed (Polygonum sachalinense)

At a glance

Cultivation

Propagation

Edible uses

Material uses

Habitat

Native range

Same genus