Identifying Bulb Types

Figuring out bulb types means understanding their planting needs.
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Photo By: Image provided by Felder Rushing

©2008, Dorling Kindersley Limited

©2011, Dorling Kindersley Limited

Photo By: Photo by Lynn Coulter

©2008, Dorling Kindersley Limited

©2011, Dorling Kindersley Limited

©2008, Dorling Kindersley Limited

©2011, Dorling Kindersley Limited

©2008, Dorling Kindersley Limited

©2011, Dorling Kindersley Limited

Photo By: Image courtesy of Longfield Gardens

©2011, Dorling Kindersley Limited

Photo By: Photo by Felder Rushing

Understanding Bulbs, Rhizomes, Corms and Tubers

Bulbs are among the easiest plants to grow, and spring-flowering bulbs in particular, such as daffodils and tulips, provide weeks of color at a time when few other plants are in flower, all with little to no fuss. Botanically speaking, bulbs are geophytes, which are herbaceous plants with underground storage organs. Geophytes don't just include true bulbs, but also those that we collectively refer to as bulbs, which are in fact corms, rhizomes and tubers.

True Bulbs

A true bulb, such as an onion, consists of fleshy layers of leaves that store food for the developing plant. The roots at the bulb's base anchor the plant in the soil and absorb nutrients. The central tip at the top of the bulb is the bud from which leaves eventually emerge. Other examples of true bulbs include daffodils, tulips, lilies and garlic.

True Bulb: Onions

True bulbs are made of leaves layered with a papery skin, like onions.

True Bulb: Lily

Lily bulbs are looser in form, and lack a papery skin. They need to be planted in the fall so they have time to develop roots; their flowers will appear the following spring. The bulbs can be divided gently and replanted after the blooms are finished.


Corms, such as gladiolus, contain a solid mass of stem tissue, rather than concentric rings of leaves. Corms are the thickened base of the stem. They have 1-2 buds at their apex. Tiny cormlets may grow around the base.

Corm: Crocus

Crocosmia, crocus, freesia and bananas are corms. On the outside, corms look a lot like bulbs. The difference is they are actually fattened base of stem itself. A corm is a solid textured food supply for stem above. As the plant grows and blooms, it consumes the food in corm, and corm shrivels and dies.


Rhizomes are swollen stems, which usually grow horizontally near the soil surface, and have several buds along them.

Rhizome: Canna

The fleshy portion at the roots of a canna is a rhizome. Some other, best known rhizomes are ginger, bamboo and many irises.


Then there are the tubers, the most well-known of which is the potato. A potato is technically a stem tuber, meaning that it's actually a swollen stem, or more correctly, the swollen tip of a rhizome.

Tuber: Potato

Shoots develop from the buds or eyes on the potato, and much like a rhizome, you can cut the tuber into pieces. Each piece will develop into a mature plant so long as the cut piece has at least one eye. You can do likewise with dahlias; they are examples of root tubers, which develop from the root rather than the stem.

Tuber: Dahlia

Tubers come in two types. Root tubers, as in dahlias, have buds at the stem base. 

Tuber: Cyclamen

Stem tubers, as in cyclamen, have surface buds.

Know Your Bulbs

All geophytes - whether true bulbs, corms, rhizomes or tubers - have one thing in common: They all require a dormant period. Depending on the geophyte, that period will be either summer or winter. Understanding the dormant period of bulbs and other geophytes is the key to growing them successfully. Unless the climate in your area is similar to the bulb's native environment, you'll have to take extra steps to grow them in your garden. That's why, for example, northern gardeners have to dig up and store tender bulbs during the winter, and southern gardeners have to pre-chill bulbs to trick them into blooming.