Although bulbs have their own food supply to carry them through until next season's blooms, an additional feeding each year with commercial fertilizers can guarantee their performance and good health.
Fertilize established beds in mid to late fall at the time when bulbs are establishing deeper roots and preparing for winter. The best ratio of fertilizer is a 9-6-6 of N.P.K. To understand this ratio, you can get and undertsanding while you link here to Fertilizing Lawns.
Use a slow release formula and sprinkle over the ground about a rate of one pound per 100 square feet.
If you fertilize your beds regularly this additional feeding isn't really necessary but if you don't fertilize at all, this fall fertilizer will produce the best results. It gives your plants a great head start in spring and helps keep them comfortable if you have encouraged deeper roots for over wintering.
Putting down mulch in the fall also creates an environment that's healthier for the root systems. If you already have mulch, double check to see that there is a good thick layer; at least 2 inches thick.