Flowering bulbs are not always bulbs…sometimes they are corms, or tubers, but we usually designate plants that grow from an underground food storage unit as a “bulb”. They are grouped as geophytes, herbaceous plants with underground nutrient storage. They all require a period of dormancy.
True bulbs are a food storage unit for the flower and plant, they have a “tunicate” papery sleeve around the outside. Examples are tulips, daffodils, hyacinths, alliums, and grape hyacinths.
Corms are food stored in the base of the stem with a papery tunic covering. They have a bottom, basal plate, and a top, the growing point. Crocus, spring and autumn, are examples of corms.
Rhizomes are food storage swellings that grow horizontally under the soil. Iris, Ginger, and Lily of the Valley are examples.
Tubers do not have the basal plate or the tunic covering- examples are Anemones, Cyclamen, and many of the summer flowering “bulbs” like dahlias and tuberous begonias.
A few notes about “true bulbs”
A true bulb contains a flower bud inside, a miniature though colorless version of the flower. The color develops with light exposure. The energy for the entire plant is stored inside the bulb, which is why tulips, hyacinths and the like can be forced into bloom in the winter time. Changes in temperature cause the bulb plants to grow, putting down roots in the fall, going dormant during cold wintry months, emerging as the temperatures warm in the spring. A time of refrigeration mimics these stages in bulbs prepared for forcing.
A few notes about “corms and tubers”
Corms and tubers need a bit more sustenance from their soil- good soil fertility and more moisture. they also have a dormant period , and that is when they are planted. Some of them can be hard to figure out: which is the bottom and which is the top? Crocus corms are like a flattened chocolate drop, a tiny growing point cues you in to the top of the corm. Many summer flowering bulbs are corms or tubers.
Dutch bulbs are some of the first things I planted when starting out gardening on my own, and no wonder, since they are among the easiest, most satisfactory blooming plants for your landscape. Thanks to the Holland bulb industry! Once started, you soon find out there are lots of innovative designs using them, and following a few tips and techniques will give you a spring landscape bursting with blooms and fragrance. Don’t stop with bulbs, add in spring flowering shrubs, too.