A bulb is a nutritional unit that sustains the plant when it is too cold or hot to flower. It helps the plant to survive by storing food during its dormant period (from late spring when the foliage dies to early fall when roots form for a new growth cycle), and it provides nutrients during the growing and flowering season.
The term “bulb” has become a catchall for the four major types of underground storage units. They all perform the same basic function.
- True Bulb — includes hyacinths, daffodils and tulips.
- Tuberous Root or Tuber — includes dahlias and some begonias. Fleshy rooted daylilies are similar in appearance.
- Corm — includes crocuses and gladioli.
- Rhizome — includes bearded irises and cannas.
Bulbs are further classified as hardy and tender. Hardy bulbs are cold-tolerant and can survive in the ground during the winter. They need the cold, chilling period of winter to perform at their best. In Southern climates where there is little or no frost, it's a good idea to dig these bulbs up every couple of years and store them in the refrigerator during the summer to simulate winter so they will keep blooming year after year. Hardy bulbs are planted in the fall and are typically spring-flowering. Hardy bulb varieties include tulip, crocus, daffodil, hyacinth, anemone and iris.
Most tender bulbs are called summer bulbs, but there are several varieties that bloom in the fall. Tender bulbs are cold-sensitive and may not be able to survive the winter in areas of the U.S. other than the Southern coastal regions, the Southwest or coastal areas of California. Unless you live in these climates, you will need to plant tender bulbs in the spring after the ground has warmed up and dig them up in late fall for winter storage. Some tender bulb varieties are elephant's ear, caladium, gladiolus, canna and dahlia.
When selecting bulbs, choose large firm ones that will produce the most flowers. Select them much like you would choose an onion or piece of fruit. A nick or small blemish is of no great concern, but avoid soft or moldy bulbs. Also, be sure they are free from visible disease and damage.
The bloom cycles listed below are for general reference. The flowering sequence depends a great deal on the weather in your region as well as the variety of bulb you plant. Planting a mix of these varieties will provide color from spring into fall.
- Very early spring — Crocus, snowdrop
- Early spring — Daffodil, crocus, hyacinth
- Mid-spring — Daffodil, fritillary, tulip
- Late spring — Fritillary, bluebell, lily
- Early summer — Allium, lily, iris
- Mid-summer — Lily, gladiolus, dahlia, iris
- Late summer — Lily, dahlia