Lemon balm? They selfseed everywhere but a nice herb to have.

thanks i dont know why they are there ? a mystery thanks anyway

If they are lemon balm they make a lovely calming tea. Put a sprig in a teapot or cafetiere and pour boiling water on. Let it stand a few minutes. then smell it - should smell pleasant and a bit lemony. I used to make this tea when I'd had a tough day at work and found it very soothing.

Seeds can lay dormant in the soil for a while before they germinate and birds drop seeds everywhere.