How deep do Japanese knotweed roots go?

The rhizome (underground stem) can extend to around 2-3 metres deep and spread several metres horizontally. Historically a figure of up to 7 metres of horizontal spread was used, though research and RICS guidance suggest the spread is often less than that in practice.

Can Japanese knotweed grow back from a small piece?

Yes. A rhizome fragment weighing less than a gram - smaller than a fingernail - can regenerate into a whole new plant. That's why cutting, digging or moving soil so easily spreads it.

Does Japanese knotweed grow in winter?

Not above ground. In winter the canes die back to brown, hollow stems and the plant looks dead. The rhizome stays alive underground and sends up fresh red shoots again in spring.

How Fast Does Japanese Knotweed Grow?

Q: How fast does Japanese knotweed grow?

Very fast. In late spring and summer it can grow up to about 10cm a day, reaching 2-3 metres tall in a single season before dying back in winter and regrowing the next year from the same rhizome.

Above ground: astonishingly fast

Once the soil warms in spring, knotweed puts on growth that few garden plants can match. At its peak in late spring and early summer, healthy stands can extend by up to 10 centimetres a day. From bare ground in March, it can form dense stands 2-3 metres tall by mid-summer - which is why a stand that looked like nothing in early spring can dominate a garden by July.

Below ground: the rhizome

The visible canes are only half the story. Underground, knotweed grows a network of woody stems called rhizomes - this is the plant's engine, storing energy and sending up new shoots. Snap a cane and you'll find the inside is dark orange; that's rhizome material.

Depth: commonly cited as reaching around 2-3 metres deep.
Spread: several metres horizontally. The old rule of thumb was up to 7 metres, though modern research and RICS guidance suggest the real spread is often less.
Resilience: a fragment weighing under a gram can grow a brand-new plant.

Why it regrows from nothing

Because any piece of rhizome can regenerate, knotweed spreads most easily when it's disturbed - cut, dug, strimmed, or carried in moved soil. In the UK it rarely spreads by seed; almost all spread is from fragments. This is the single most important thing to understand: disturbing knotweed is how you spread it, which is why cutting or digging is the wrong instinct.

See red shoots in spring? That early, asparagus-like growth is the easiest time to catch knotweed - before it towers overhead. Learn the tell-tale features by season.

Growth through the year

Spring: red-purple shoots emerge and rocket upward.
Summer: tall green bamboo-like canes, dense leaf cover, peak height.
Autumn: creamy-white flowers, then leaves yellow and drop.
Winter: hollow brown canes; dormant but alive underground.

Why the speed matters

That growth rate is why knotweed is treated so seriously: left alone, a small clump becomes a large infestation in a couple of seasons, pushing into cracks in hard surfaces, boundaries and drains, and becoming far costlier to remove. Catching it early - while it's a manageable patch - saves money and stress.

Caught it early? Confirm it fast

The sooner you know, the cheaper it is to deal with. Snap a photo with KnotweediD for a verdict in seconds, plus optional confirmation by a PCA CSJK accredited surveyor.

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Frequently asked questions

How fast does Japanese knotweed grow?

Up to around 10cm a day in summer, reaching 2-3 metres tall in one season.

How deep and far do the roots go?

The rhizome can reach roughly 2-3m deep and spread several metres horizontally; the old "7 metre" figure is now considered a worst case rather than the norm.

Will it come back after winter?

Yes - the top growth dies back but the rhizome survives and regrows each spring until it's properly treated. See how to get rid of it.

Written by Alexander White PCA Certificated Japanese Knotweed Surveyor (CSJK) About our surveyors →

This guide is general information. Figures for rhizome depth and spread vary by site and source; for an assessment of extent, use a PCA-accredited Japanese knotweed specialist.