should I put bark down on a sloped bank until ground cover matures?

Well it won't do any harm, but if the slope is steep enough, it might wash off in the rain!

Thanks, I have no concept of what degree the slope is, but I suppose I could buy a bag of bark and see what happens. Its more for keeping the weeds/grass at bay where I havent totally gotten the roots out, or where it is seeding again.

Shel if you haven't got the roots of your weeds out they will grow up through the bark. Bark will, on the other hand, stop the seeds from getting into the ground and growing. With the couch grass you are going to have an ongoing problem it it is in the field next to you. I'd separate the flower bed from the field about 6 inches in from your boundary using something that you can bury in to a depth of a foot or even more. I'd then keep spraying the sacrificial bit with roundup - making sure it did not get on any other plant!

I know i'm tired, but I'm shocked to realise I didn't read all of your question properly! Moongrower's suggestion re the couch grass is a good one - nothing will smother it, it will smother everything else. And, as MG says, if you haven't got all the roots out, it will grow up through the bark, whatever the weed is - if you see regrowth from something you've not got out properly the first time, have another shot at digging it out completely as it appears.

There are whins(gorse) on the other side of the wire as well, in the field, but the roots (or some of them) are within my bank so I dont think I could dig down a foot into. It really is a nuisance bit of the garden, and I just wanted something low maintenance but tidy looking.

Shell I don't think you are going to have a low maintenance solution unless you can stop the couch grass invading. It will continue to do so no matter how much you weed it out. Just hack away at the roots of the whins as you go down until yet get to a good foot below the surface. It sounds as if it is a farmers field on the other side and he is not going to be interested in keeping the whins under control and, to be honest, I am glad of that they are home to a lot of wildlife. Even sinking in old corrugated metal sheets will help!

what ever you plant ,build etc i would consider about a foot or 2 of your garden wear the couch grass is a loss and build a raised bed,pond etc out of heavy blocks in front of this .it may cost a bit but as moon grower sais anything else just wont be easy or it wont work.