I agree with Eric, and now for the bad news, this plant is so very invasive and difficult to remove. Pulling it out is one way, but leave a very tiny bit of root behind and it will be back again. If you don't mind covering the ground this year with a fabric or cardboard, then by doing this it will starve it of light and kill it. But if your neighbours have it, then the seed will get back into your garden and off you go again. So be aware of this. In the UK people buy this and plant it in their gardens due to the pretty purple flowers, only to regret their decision, their neighbours included. It will take over if you don't start a remedy soon.
It is not on the neighbours lawn near mine there was only 1 patch there are 2 more about 10 feet from the first it has never flowered so how did it move
It must he close by somewhere Dave. Thousands of seeds in a strong wind can travel a very long way though. If you don't have many, I would suggest removal ASAP and especially before flowering and seed drop.
