Tackling this plant yourself there are several approaches you could take with varying effectiveness and risks attached. Probably the most effective and least risky approach is herbicides, applied either through spraying or through injection. Another option is to try and dig the Japanese knotweed up, this is fairly risky and likely not to produce results unless done professionally, this is because Japanese knotweed will grow back from very small amounts of the rhizome meaning you have to get the whole plant dug up and then find every single piece. Any soil or parts of the plant are then considered controlled waste, which need to be disposed of properly, which can be costly. The third method is to cut the plant down and then cover it with tarps to stop sunlight getting to it. This method will need a huge amount of work, but doesn’t use herbicides. Keep in mind though, that this method also has the issue of producing controlled waste
As for the time to attack; the answer has to be as soon as possible; Japanese knotweed grows at alarming rates and every day it’s left to its own devices, it’s gaining a stronger foothold in your property. The best times to spray it is any time after it’s started to grow, you can expect it to really kick off growing around May time, so be on the lookout from the end of April. Another factor to consider with spraying is that it’s friendlier to bees if you don’t spray it at the end of the summer when it will be flowering.
Always remember as well, once you begin you need to keep the work up, it can take years to fully eradicate a Japanese knotweed, you need to keep at the work and be ready for when it grows back, wherever it may sprout up.
