Japanese knotweed

Value to bees

Nectar

Very high

Pollen

Moderate

As a honey crop

Major honey crop — yields a surplus in good years

Which bees, and why

Worked heavily in September by honey bees and late bumblebees. In Britain nearly all plants are female clones of a single introduction and set no viable seed, so the bees gain nectar and the plant gains nothing — it spreads entirely by rhizome fragments.

Worth knowing

An excellent late nectar source, and moderate for pollen.

Flowering

In flower

August to October (northern hemisphere)

Very late, which is the source of both its value and its reputation among beekeepers.

When nectar flows

Heavy from established stands, and at a time of year when colonies would otherwise be consuming their stores rather than building them.

Year-to-year variation

Reliable where stands are large, which they generally are. In the northeastern United States it is a recognised commercial crop sold as bamboo honey.

What it does to the honey

Dark amber, buttery and rich with a distinct mild tang, frequently compared with a light buckwheat honey. It is a genuinely good honey from a genuinely bad plant.

Growing it

Conditions

Almost anything. Sun or shade, wet or dry, and it regenerates from a rhizome fragment the size of a fingernail.

Size

2-3 m tall, spreading by rhizome into dense stands.

Native range

Japan, China and Korea, on volcanic slopes where it is a pioneer species and entirely unremarkable. Introduced to Europe in the nineteenth century as an ornamental.

Suits

Farm scale

What it looks like

Tall hollow bamboo-like stems, often speckled purple, with broad shield-shaped leaves in a distinctive zigzag arrangement, and loose sprays of small creamy-white flowers in late summer. It dies back completely to bare canes in winter.