Green is the most difficult color to come by with natural dyes. With all the greenery that is around us, very few plants will actually yield any kind of usable green dye. It seems that in the 18th century, green was primarily made by double dying, blue and yellow (usually indigo and weld, or maybe "Quercitron" oak bark)
I went out the other day, and couldn't find any nettles at all. I found that Plantain roots are supposed to make a green dye. Well, I got zillions of them growing in the yard, and I pulled up a big mess of them and boiled them up. With that, and some Queen Anne's Lace I threw in, and a ferrous sulphate mordant, I got a very attractive sage green.... but unfortunately, a VERY light sage green, barely darker than the natural color of the linen. I suspect that wool would have dyed more readily, as wool always dyes better than cotton or linen.