If you’ve spent any time around gardens, allotments, or even property news headlines, you’ll know the name Japanese Knotweed (Fallopia japonica). This notorious plant is one of the most invasive species in the UK, and one of the most destructive.
Why You Shouldn’t Grow Japanese Knotweed
- Highly invasive: Knotweed spreads underground through rhizomes, with fragments as small as 2cm capable of creating a new plant.
- Structural damage: It’s infamous for pushing through tarmac, paving, and even building foundations.
- Costly to remove: Professional treatment is often required, and removal costs in the UK are estimated in the hundreds of millions every year.
- Legal restrictions: It’s an offence to plant or cause Japanese Knotweed to spread in the wild under the Wildlife and Countryside Act 1981.
How to Spot It
- Stems: Bamboo-like, hollow, with purple speckles.
- Leaves: Shield-shaped with a pointed tip, arranged in a zig-zag pattern along the stem.
- Flowers: Creamy-white clusters appear in late summer.
- Height: Can reach up to 3m tall in a single growing season.
Why It’s a Problem for Gardeners and Growers
For allotments and gardens, Japanese Knotweed is more than just a nuisance:
- It spreads aggressively, smothering crops and outcompeting vegetables for light and nutrients.
- Once established, it’s almost impossible to eradicate without expert intervention.
- Its presence can even reduce property values and complicate mortgages.
What to Do if You Find It
- Don’t compost it: Knotweed is a “controlled waste” under the Environmental Protection Act 1990. It must be disposed of at licensed landfill sites.
- Don’t try to dig it out: Any missed fragments can regrow.
- Seek professional help: Specialist contractors can advise on the safest removal or management options.
Final Word
Japanese Knotweed may look like just another ornamental plant, but the damage it causes makes it one of the most dangerous plants you can have in your garden. That’s why it firmly belongs on our No Grow List.
If you want to fill your plot with vigorous, long-lasting growth, we recommend focusing on crops that repay your effort rather than threaten it. Explore our Crop Spotlight series for ideas on what to grow instead.
