You would need to add lots of nitrogen to grow anything well. As the stump rots it uses up nitrogen.

Lee

you might try using annuals in the stups with a pocket of potting mix.
also you might consider using a chain saw to carve a depression in the top of the stump-- make criss cross cuts
about 4-5 inches deep and then use a hammer/chisel to know out the wood-- to make a bird bath-- which would be appreciated.
also you could let a climatis climb over the stump

but like lee said you will need to fertilize a perennial
because of the nitrogen the wood will use to decay.
digger2

Thanks for your responses. I think I'll plant the cotoneasters to the sides of the stumps and train them over to give a knarly green carpet effect--then she can place a series of tall pots with whatever she wants among the cotoneasters to give her height at the back of the border.

I'm out of my element here because she is "blessed" with too much sun and I'm used to working with part sun at best.

When I was at Callaway Gardens in Georgia I saw the prettiest bird bath. They had hollowed out the middle of a tree stump and lined it in cement, bringing up a bit of a lip. They mounted a china bird right on the edge, in the concrete. It was so natural and lovely.

I was also going to suggest using stumps as base of a focal point, pots, statue, bird bath, large decorative rock. I have one at the edge of a bed that I use for rock collected on trips. I can lay them out and not have them disappear into the dirt like edging rocks will. Also nice to set tools on stump, easy to find on next trip thru. I will miss my stump when it finishes decaying.