Posted: 17/04/2014 at 21:20
Sorry to learn of your problem. There is something about some weeds, that still present a mystery. My eldest daughter lives in the New Forest. Keen gardener like her dad. She has had the fight againt ground elder for yonks. One common factor is. I know of individuals who have had the money etc, to actually go as far as having loads of soil removed and replaced by fresh imported soil. Then blow me down. Next season. There it is again. Firstly. It is difficult to eradicate, even with modern chemicals. Might I suggest. That you take a look over the fence, and your local/immediate area. In some instances, plagued gardeners have practically got rid of it. However it comes back. For some unknown reason. Growths way beyond your garden could house the source. It is as though, similar to slugs and snails. As if in some way, a kind of scent trail is left behind. Honestly. It is one of the mysteries of gardening. I would be inclined to, if possible. Try burning. This is easy on a blank canvas, however in a planted border, not so easy. Basically, one would burn off the surface of the soil, with a flame gun. Then dig the area over, and burn the fresh soil. This helps to destroy bits of roots, which chemical wouldn't reach. Sad to say. Even then. It is likely to return.
I wish all the best. Frequent hoeing will keep it out of sight, but below decks, it will flourish. Good luck.