It depends a bit which weeds, and what their method of spread is. In almost any case, the black plastic edging will probably be a waste of time. Weeds that spread by runners, like daylilies or morning glory, will easily bypass even quite deep edging, and most weeds spread by seed so will come through the fence. As such, if you add some boards to the fence from the ground up you might make the most impact, but even that will be bypassed by seeds to some degree. But for seed-sown weeds, to some extent you can depend on the shade your plants are going to supply to limit the degree to which weed seeds find hospitable ground on your side of the fence. The better your shrubs cover, the less weed growth you will have... "the trick is to cover the ground," as a nursery near me once wrote in their catalogue. As your plants grow in, their root competition will also help to reduce weeds. The real key to ongoing success against weeds is to design into your border the capacity for you to get into that area and pull weeds early, and probably also to put down an annual covering of mulch. Either open areas or stepping stones, in other words, which will not show much among your plants in summer, and can maybe add a nice structural/pattern design element in winter. What you can also do is plant a groundcover that you like that will grow over toward your neighbour and maybe suppress his/her weeds a bit, or a lot. In my climate something like Asarum canadense would do the trick. But you have to want it in your border too! Ongoing vigilance and access, and discreet use of herbicide on weeds that grow by runners, is the nutshell answer that I would offer. That, at least, is how I approach my neighbour's weeds, which include morning glory and buttercups, and so attack via underground runners, surface runners, and seed through a spaced-board privacy fence. Karin L

You could rent a ditch witch and dig a retaining footingÂ..seems a bit extreme. Would it be cheaper to put in some edging? The stuff below is 4Âx1 http://www.lowes.com/pd_27876-304-8848_4294857252+4294961918_4294937087?catalogId=10051&productId=3142289&Ne=4294937087¤tURL=%2Fpl_Easy%2BGardener_4294857252+4294961918_4294937087_&N=4294857252+4294961918&identifier=Easy+Gardener&langId=-1&storeId=10151&ddkey=http:CategoryDisplay At $6 per 4ÂÂfigure three per side, times four sides. $72 plus tax. Might be cheaper than a $40 dollar tool rental plus what ever material you are using to retain them. But I am cheap and have kids "hey, go bury that railroad tie next to the raspberries." ( joking )

Thanks to all for the replies. kato_b: I don't think grass would work. It's kind of an awkward area, which is probably why someone planted ivy there. There's a rock retaining wall at the back of it, cement stairs and sidewalk boardering it on one side, a cement sidewalk with raised cement border at the front and a cement slab boardering on the neighbor's side. It's also sloped. I'm reluctant to plant anything there because we've been battling poison ivy in that area all spring and I think it will continue because the neighbor isn't controlling it on her side. I don't have the patience to keep killing it off while dealing with desirable plants in the area. Is the main problem with landscape rocks dealing with the debris that gathers in there and trying to keep it looking tidy? Does plastic make it worse? Does using larger landscape rocks - like medium sized river rocks - make the problem better or worse? Wood mulch could work but I'm afraid it might tend to wash away because of the slope. Maybe I'll just let whatever the neighbor has on her side take over (except the evil poison ivy) and move on to the multitude of other projects we have to complete this summer. Gotta pick your battles. You know, gardenweb should start a forum with tips on how to live in peace with difficult neighbors who share a property line. This neighbor just cut down 3/4 of an old evergreen shrub that was on the line and left the mutilated remains on my side for me to deal with. Is that passive-aggressive or what! It's going to be a long summer.

I gotta ask...who really cares what the side facing a permanent barrier such as a block wall looks like? Of course it's gonna look sh%##y, but unless you plan on a second life as a fairy or a toad, you aren't going to be spending a lot of time looking at it...which is why you planted something in the first place, to hide that barrier and to have the much more aesthetically pleasing plant facing you, not the wall, look good. And as for width, there are solutions for that. As far as the effect of spacing on root growth, not sure anyone has the answer to that, not sure it has been studied in that way. Every spacing study i've seen is about top development, and most discussions i've had are about practical matters, such as how wide to allow for ease of digging with (brand) spade. Strictly speculating, i'd say that similar to development of crowns, closer spacing may push roots to grow where there is less competition, pushing wide out from the row, but roots also freely form grafts where ever they cross, so it may all be blowing smoke to even try to answer the question.