Picture would be useful!

As Owdboggy says, a photo would be of use here - green shoots could be anything at all. Except I'll ask you a question now - have you got sycamore trees anywhere nearby, or other trees overhanging your garden?

my garden is full of sycamore and ash seedligs. I have never seen so many as i have this spring.

That's what I was thinking about, seaburngirl, tree seedlings. But it could be lots of things.

well a weed is a plant in the wrong place so i would get some path clear as you wont get the saplings out.i would imagine this is going to happen again bye the sounds of it.the grass and patio could of bean put over weeds that were cut down and coverd with said patio and grass if you havnt bean there long.mowing or a weed killer thats made for clearing weeds from lawns will sort that out.it mite be worth just grabbing one of the shoots out the edge of your lawn.potting it up and seeing what develops.the thing is nearly all new shoots look very similer.i hope ive helped take care bye for now.
ps as bamboo sais it could be some shrub or tree hanging over or close to your garden.