Put down old carpet or thick cardboard or layers of newspaper through the winter (weighted down with bricks or stones if necessary) and in the Spring you'll have warmed, dryish soil in which the weeds have germinated then run out of light to survive. The following grow well in our extremely heavy clay: roses (old HT varieties like Peace and Josephine Bruce), phlox, Japanese anemones, hydrangea, buddleja, chrysanthemum, lysymachia, phlox, tansy, fuchsia, foxglove, sedum, hebe (wouldn't think it should, but it does), olearia.