I do believe I've finally figured out how to handle Lady's Mantle, Alchemilla vulgaris.
This plant looks wonderful in the early spring and Summer, but then you have to cut it right back, leaving you with.... yes, a big hole. And since the Lady looks best when there's lots of it to froth over rocks and paths, you tend to end up with a rather large empty space in your border. It self-seeds for me, maybe a bit too freely, so I have been leaving many seedlings and enjoying it a lot when it blooms. The chartreuse green flowers and the only slightly greener leaves make a wonderful foil for almost any colour of flowers. It sets off white Daisies, blue-violet Geraniums, pink Roses, in fact any pastel colour to perfection. Alas, it only blooms for a couple of weeks, and then it turns really shabby. And it's no good just cutting back the spent flowering stems because the leaves that accompanied them will also turn brown and tired looking and you really need to shear the whole thing to the ground.
It re-grows fairly quickly, but still for a few weeks you have a big gap.
The notion I hit on was to treat it somewhat like a rock garden plant. I mulched all around the plants with some of that lovely pea stone I lucked into last year. The plants spread and covered the gravel and bloomed wonderfully, then today when I cut them right back they went back to looking like small plants surrounded by a large area of beautiful small stones! Perfect!
I'm really liking that idea a lot! And the pea gravel makes weeding much easier. The weeds that do come up, are so easy to pull out it's actually fun!