I managed to find some nice big pots of Dichondra "silver falls". I turned two of these:
Into eight of these:
I really like how they look - the silver is a great contrast to all of that dark green foliage and the wine-red of the autumn hydrangeas. With luck by mid-summer they'll have grown long and thick over the edge of the bed. I'm also thinking of planting some flowers in the beds until the hydrangeas grow up a bit - I'm thinking violas or maybe forget-me-nots. What do you think?