What Is a Plant Bulb?


A bulb is a plant that stores everything it needs to grow in an underground storage structure. There are five types of storage structures: true bulbs, corms, tubers, tuberous roots and rhizomes.

The tulip grows from a bulb. image by Image by Flickr.com, courtesy of Ruth Douillette

Bulb Life Cycle

Bulbs are usually perennial, requiring a period of dormancy after growth and flowering. They can be hardy (like daffodils and irises) or tender (like dahlias). Hardy spring-flowering bulbs end their growing season by early summer and begin to grow again in the fall, flowering again the next spring. Tender summer-flowering bulbs must be dug up after flowering and stored indoors for the winter.

True Bulbs

True bulbs are either tunicate (having a covering that prevents the bulb from drying out) or imbricate (in which the bulb's fleshy scales have no covering). Tulips, daffodils and hyacinths are tunicate bulbs. The lily is an imbricate bulb and must be kept moist when it is out of the ground.


A corm consists of a compressed stem that is a storage structure. Gladioluses and crocuses are corms.


The surface of a tuber is covered with buds from which the shoots and roots grow. Caladiums and anemones are examples of tubers.

Tuberous Roots

Tuberous root plants, like the dahlia and some begonias, store plant reserves in an actual root.


Rhizomes grow horizontally underground. Irises and lily of the valley are examples of plants that spread by this method.


  • University of Illinois Extension
  • University of Minnesota Extension
Keywords: bulb life cycle, true bulbs, corms, rhizomes, tubers

About this Author

Gwen Bruno has been a full-time freelance writer since 2009, with her gardening-related articles appearing on DavesGarden. She is a former teacher and librarian, and she holds a bachelor's degree in education from Augustana College and master's degrees in education and library science from North Park University and the University of Wisconsin.