Feeding

I'm trying to get more disciplined in feeding my plants... the roses I feed with rose food, and the clematis with clematis food, the shrub bed I leave pretty much to its own devices, but what is the best way to keep the mixed herbaceous perennial bed fed? Pellets or liquid feed? How often? I try to mulch it in the Autumn, but it is very full, so it can be a bit tricky. 

It's full of cottage garden staples (geranium, astrantia, aquilegia, roses, echinacea, agapanthus, salvia, alstroemeria, japanese anemones, monarda, penstemons, lupins, delphiniums, echinops, persicaria... so a real mix), and the soil tends to be quite clayey. 

Many thanks.