Some bulbs need to be planted in the spring; others do best when you plant them in the fall. When to plant bulbs depends a lot on when your bulbs will bloom.
Bulbs aren't instant-gratification plants. They need some time in the ground before they send forth stem, foliage, and flowers. But they're not inert when they're in the ground, of course. They're generating root growth, which will help nourish the show as well as anchor the plants in place.
The following list provides some general guidelines about when to plant your bulbs:
Planting spring-blooming bulbs: Spring-blooming bulbs require a chilling period. They're dormant when you get them and break dormancy only after the chilling. Winter conveniently supplies this necessary cold period! That's why you put the bulbs in the ground the fall before you want them to bloom.
Planting summer-blooming bulbs: Most summer-bloomers, such as gladioli, calla lilies, dahlias, tuberous begonias, and crocosmias, love warm soil and toasty summer sun. If you garden in a mild climate (Zones 8 to 10), you can plant these bulbs in the early spring and expect flowers by summer. If you garden in a colder area, early spring planting isn't feasible. Instead, wait until late spring or early summer — the same time locals plant tomatoes outside — or start bulbs early indoors in a warm spot and care for them until danger of frost has passed; then you can move the plants outdoors.
In either case, regular doses of all-purpose fertilizer (applied according to label directions) can nudge your plants into faster, more robust growth and more and better flowers.
To get flowers earlier and longer from these summer bloomers, visit a nursery in late spring or early summer (or place your order then with a mail-order house, either via catalog or Web site) and buy a larger, pre-started plant.
Planting fall-blooming bulbs: Spring gets all the attention, to be sure, but some bulbs bloom in fall, and they're gorgeous and easy to grow — and they're a wonderful sight to behold when the gardening year is winding down. Among this group are the autumn crocus (Colchicum autumnale — no relation to true crocuses — or Crocus speciosus), winter daffodil (Sternbergia), Guernsey lily (Nerine bowdenii), saffron crocus (Crocus sativus), and even a species of snowdrops (Galanthus reginae-olgae). If your local garden center doesn't have these, look for them in specialty bulb catalogs or on gardening Web sites.
Fall-blooming bulbs have a dormant period, too: summer. Thus, you ought to plant them in late summer — as soon as they're available — because the plants are ready to wake up. Some bulbs, like the autumn crocus, send up their leaves in spring and flower leaflessly in fall. Usually, these bulbs spring to life soon after planting — within a few weeks — though you'd best mark the spot so you don't forget them and plant something over them. In any event, the flowers will arrive on schedule.