| I would take a look around at the indegenous plants- first of all, is that purple clover, or 'crown vetch' which has a more vining habit, and larger flowers? it's a good erosion control plant, but I like it WITH something, instead of all by itself- and honestly, it's root diversity that will hold a slope together. around here, the local daylilles are free for the digging in the spring along the roadsides everywhere. and they spread fairly quickly, if they like the situation they find themselves in. standing sedums are amazingly easy to propagate- break off a branch (or a leaf) let the end dry, stick it in damp potting soil, and leave it in the shade for a week. it will put out roots. one plant will make 15 babies will be 15 flowering-sized plants the next year. :) and then there's the bully. http://hortiplex.gardenweb.com/plants/p1/gw1021851.html I adore this plant. love it, love it, love it. it speads like bad gossip, lives in the worst soils, and can take full sun (it's a fairly well behaved shade plant, a monster in the sun) and it's a fairly open groundcover, so you can grow tall things (like a row of burning bushes at the base of the slope, about 3' back from the retaining wall, or stands of either daylilies, or the standing 'turk's cap' lilies, or phlox, or sedums...) up through it. and I will gleefully sell you plugs for less than a buck a piece, now that my own bed is established :) | 
