Karen - we began putting a cup full of meal down every 4 weeks, just as the new shoots poked through the ground. sometime around late feb. I believe...? just worked it into the surrounding soil about two inches (or whatever?) deep. its not really a "fertilizer" perse', its more of a bloom booster of sorts, due to its high concentration of amino acids and growth regulators, so theres no need to continue once its done flowering. it wont hurt to continue using it, but once the flowers all fade and drop off, thats when I switch to liquid fish; until mid august. then I stop with the fish so the plant can prepare for dormancy.
P.S. - alfalfa meal is great for most flowering plants; clematis, day lilies, lily bulbs, peonies, and especially roses, and ESPECIALLY dahlias!! use two full cups of alfalfa meal per dahlia bulb and you'll have blooms coming out your ears!!