Hardy vs. Tender Bulbs
By: Julie Day
“I’m confused about bulbs. What’s the difference between hardy bulbs and tender bulbs? And what about spring vs. summer bulbs? How do I know what kind I can grow?” -Scott
Let me start by defining the two most important things you need to know:
- Hardy bulbs require a period of cold in order to bloom. These bulbs are planted in the fall and bloom in spring or summer. You can force hardy bulbs to bloom most any time by chilling them for 2-4 months, which fools them into thinking they’ve had winter.
Examples of hardy bulbs include: tulips, daffodils, grape hyacinths, and crocuses.
- Tender bulbs do not need, and cannot survive, cold temperatures. They respond more to the length of daylight and to warmth, and they are usually planted in the spring to bloom in summer or fall. You can’t force them to bloom unless you have a greenhouse that controls light, temperature, and humidity, but you can give them a head start by potting them indoors in early spring.
Examples of tender bulbs include Canna, Calla, Elephant Ear, Caladium, Ranunculus, Dahlia, Gladiolus, and Tuberous Begonia.
Some bulbs are only semi-tender, meaning that some areas of the U.S. can grow them year-round. Others are tropical and cannot tolerate any cold at all. When buying bulbs, be sure to check the hardiness zone to see if you can leave them in the ground over the winter. If your climate is too cold, you can always dig up and store your tender bulbs over the winter, and replant them in the spring.
As for the question about spring vs. summer bulbs, that’s just an indicator of when they bloom. All spring bulbs are hardy, but summer bulbs may or may not be hardy depending on the type.