Aahhh, it's the dreaded himalayan balsam plant! Get it out quick, it'll take over your garden!!

It is himilaian balsam and an invasive self seeding garden escapee. Remove it before it sets seeds or you will have hndreds next year.

Ahh no! The deadly Himalayan Balsam! Please don't compost it...bin it or burn it.

Agree with all. I would add that Himalayan Balsam loves wet conditions whilst acers do not - is your container too wet for the acer.

Thanks to everyone for identifying the Himalayan balsam as not to have in a garden.When I read the comments I went straight out with secateurs cut all the flower heads off along with the stem in two or three pieces and pulled the remainder out roots and all wrapped the lot in newspaper and put it all in the incinerator with a fire lighter and burnt the lot.The acer has probably been wetter than normal because of the weather.It was looking a bit sorry for its self.So I will keep a close eye on it now as its about eight years old and still a fine specimen Thanks again Dave

I would keep an eye out Dave and make sure it hasn't self-seeded into the pot!!

Hopefully I,ve caught it before it set seed in the pot as I guess it forms seeds on the plant itself after the flower stage but I will check often to make sure.Thanks again

I have a wood full of this stuff. and it's not particularly wet but it is shady (obviously) which it also loves. I harvest the seeds, they're edible and taste nutty. But you have to catch them before the pod bursts and seeds the seeds a long way. They are an annual.