Spring is the point to catch Japanese knotweed early, because the shoots that appear are distinctive and a stand caught small is simpler to deal with. From around March, red and purple asparagus-like shoots push up fast from the crown where last year's dead canes stand, unrolling into red-speckled stems with rolled-up heart-shaped leaves. These shoots appear before most look-alikes leaf out, so our guide on how to identify it treats them as one of the most useful early signs of the year.
What do the spring shoots look like?
The spring shoots look like red or purple asparagus spears, tightly rolled and pushing straight up through the soil, often clustered around the standing brown canes from the previous year. As they grow they unfurl into green stems flecked with red or purple, carrying young leaves that start heart-shaped and roll open into the mature shovel form. This is the fastest growth of the knotweed year, with a stand climbing at up to around 10 centimetres a day and reaching full height by early summer.
Where do the shoots come from?
The shoots come from the crown and the rhizome, the underground stem system that survives the winter dormant and stores the plant's reserves. New canes emerge from the crown at the centre of the stand and from rhizome that can run several metres out, which is why fresh shoots sometimes appear a distance from the obvious clump. Recognising that the shoots mark a living rhizome system below ground explains why pulling them does not clear the plant.
How do I tell spring shoots from other plants?
The tells are the red or purple asparagus-like spear rising from bare soil near old canes, and the way it unrolls into a red-speckled hollow stem with alternating leaves. Bamboo shoots are woody and round without the red speckle, and most garden perennials leaf out differently and later. Because young knotweed leaves can briefly resemble dock or lilac, a photograph of the shoots and any standing dead canes is the safe way to be sure of a small spring stand.
Why act in spring?
Acting in spring matters because a stand identified early is smaller, cheaper and quicker to bring under control before it reaches its summer size. Stem-injection treatment begins once the canes are established, and knowing the extent early lets a survey map the rhizome before the growing season is well under way. Spring also aligns with the buying and selling season, so an early confirmation gives a mover time to arrange a survey and a plan before it holds up a sale.
Common questions
- Can I dig out the spring shoots?
- Digging rarely clears knotweed and risks spreading it, because any rhizome fragment left behind or moved can regrow. The excavated material is also controlled waste. Treatment or a professional dig-out is the reliable route.
- How quickly do the shoots grow?
- At their spring and early-summer peak the canes can extend by up to around 10 centimetres a day, reaching 2 to 3 metres by early summer. That speed is one reason a small spring stand should not be left.
- Do the shoots appear at the same time every year?
- They usually emerge from around March into April depending on the season and the site, earlier in a mild spring or a sheltered spot. A cold spring can push the first shoots back by a few weeks.