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Japanese knotweed, Fallopia japonica, was introduced to the UK by the Victorians as an ornamental plant. But because of its rampant growth, and the fact it aggressively over-runs anything in its path, it's now an offence to plant this in the wild. It spreads by sprouting from thick, woody rhizomes, and can grow 1.2m in one season. Winter is the only time of year that offers a reprieve, but for the rest of the year it's a plant that needs tough handling as soon as it appears.
Solution
Organic
Weaken the plant by cutting off the top growth every two to four weeks. Let the cut stems wither in the sun until dead before digging up and disposing of them. Do not add them to the compost heap. If you dig up any rhizomes, you must take them to a licensed waste site, as they are a 'controlled waste' under the Environment Protection Act 1990.
Chemical
Use a total weedkiller, such as glyphosate. For best results, cut away old stems in winter and spray the plant in late summer when the weed is flowering. You will need to re-apply in midsummer, then check in September and spray again if needed. Check again in spring. It can take 3 or 4 seasons to eradicate using glyphosate. Avoid spraying on a windy day and near other desirable plants.
