You also need to consider that annual grasses sown in spring such as oats will flower and produce long tillers and eventually seeds. This is where perennial clovers have there advantage (they seed and flower in the second year). I also add cornflowers, marigold, calendula and some kind of umbelliferae (dill, fennel) to attract insects.

Another technique I use when I have bare ground is to sow Phacelia, Mustard, Summer Vetch, Buckwheat and Peas as early as conditions allow. These are all easily killed by mowing close to the ground. I plant them in 4 rows per bed so that I cab sow/transplant 3 rows of crops (in between the residual roots) directly after mowing.