Yes it is evergreen however how do you propose to contain it from entering your neighbors garden? That is a problem and yes you must prune it in the fall to prevent it from invading your flower garden. You must be careful or suffer the consequences. It loves a mosit soil so amend your soil accordingly. Unfortunatley I have a neighbor similar to you however nothing will grow as high to protect me from their junkyard, except code enforcement.

Here is a link that might be useful: Propagating Perennials

Thanks bullthistle,
Normally I would be very concerned about invading the neighbors domain, I have always tried to treat neighbors as I have wanted to be treated. But I have tried everything with this neighbor. We have reminded them when "free" yard waste removal is in our area, so they could get rid of it free of charge. We have even offered to haul it with ours on those free days. We have tried spraying weed killer on the larger (4ft) tall weeds, even though I try to keep my yard chemical free. we have hacked away at the ones we can reach from our side and asked if we could come on their side of the fence to hack away from there. Nothing seems to get through to them and still the pile grows and now there is a very invasive "wild morning glory" that is growing in this pile that really chokes out anything it touches. I pull it out whenever I see any but it's a constant battle. I'm hoping I can grow something that chokes out their weeds, covers up their yard waste, doesn't loose it's leaves in the winter and looks nice from my yard without messing up the garden I have planted.
I tall order I guess, any other ideas would be greatly appreciated. fencing the area would be my dream, but that would be too expensive.