I want to fill in an area with wild flowers and perennials, but I also want walk-upon ground cover (so i can get in and weed if need be)
I'm wondering if the perennials will be able to grow through the ground cover -- i dont mind if the ground cover is invasive, since i have a large area to cover... I"m thinking about using something like Sweet Woodruff or Golden Star, would other plants be able to get through it?
Another nice groundcover that is hardy enough to walk on is Scotch moee or irish moss. It looks like bent grass (golfcourse greens) but it gets small white flowers. Latin name Sagina subulata. It totally hugs the ground and is dense enough to control weeds (somewhat)http://www.epicplants.com/tagView.asp?ProductIDTrunc=420-05
Unfortunately, weeds are generally more aggressive than wildflowers, so if the groundcover keeps them at bay it's unlikely that the wildflowers would get much of a foothold unless you're good about going in and cutting the groundcover away before it grows over your wildflowers and chokes them out (a less aggressive groundcover won't give you as hard a time on this, but it also may not control weeds as effectively)
I wonder if you really want a living groundcover though--it sounds like its purpose is to keep away weeds and give you a surface to walk on. Would you consider a non-living groundcover like mulch instead? That way you can plant whatever wildflowers you want. The mulch will keep them from reseeding, but at least the ones that you plant will be able to grow without getting taken over by the groundcover. And you can walk on it no problem to get to the weeds. It also starts working right away, rather than needing time to grow before it really will have an impact on the weeds.
I have Sweet woodruff growing all over my garden, which is mainly shadow and half-shadow. Most wildflowers love a more sunny spot, so the combination of the two might not be successful.
I know by personal experience that strong perennials like many types of Geraniums can take the concurrence of the Woodruff. It roots very shallow and can easily be held under control if you want to protect more delicate plants.
If your spot is more sunny, you could for example try different low-growing types of Thyme, they are very strong and can occasionally be stepped upon. Surplus is that they are an excellent food supply for example bees.
Wildflowers can usually take the concurrence, like one can observe in nature. The best adviser is still nature, if one take the time to carefully observe it.
In nature one can also observe that wildflowers usually live together with grasses.
But when your soil is too fertile the grasses can take over and only a few wildflowers like Dandelion and buttercups can cope with that.
An easy way to make the soil more poor is to take out the top layer (you could use in another area for the perennials f.ex.) and then sow a wildflower mix with grasses. My brother who is a landscape architect often uses this method. Very beautiful is to mow a path in the wildflower field of about 1 to 1,5 m broad.
this first image is from Google Earth
you can see a small opening in the "bush line" along the big fence, it backs to the highway
that opening (I added the pink arrow) is where I want to do the wildflowers and ground cover
and as you can see my house - my yard, fenced in, is a postage stamp -- that is why i'd working on beautifying State property.
YOU can see a "track" around the field -- my kids ride dirt bikes there -- and the "weeds" grow 4+ feet high or higher in some places
... but from where you see that "gap", there is pretty much a line from that point going east that I maintain, and everything to the south is wild.