Bulbs, Corms and Rhizomes: The Difference

By Debbie Roland and Emmy Ulmschneider, Master Gardeners

Life is all about survival. And plants are no strangers to surviving under unfavorable conditions. What if you could develop a structure that not only would store nutrients but could also foster new growth? Well, plants did just that in a variety of ways developing storage organs that could also be used for vegetative reproduction that is reproduction without flowering. Technically these storage organs are called perennating organs, but you might be more familiar with the term “bulbs.”

“Bulbs” are like storage barrels. They help plants survive when the weather isn’t suitable, think drought or an unusual cold, which means they do not flower to reproduce. Then when conditions are favorable, the plant uses the stored nutrients to grow or produce new plants.

There are different types of what we call “bulbs”.

True bulbs are the whole plant in a small package. In the bulb, the storage organs are thickened leaves (bulb scales) which surround the short erect stem. As they grow, they send up stems which is what we see above the ground. They also grow bulblets that are offshoots of the mother plant. These can be thinned and transplanted by digging up the bulb and breaking off the bulblets that have formed. Daffodils, tulips, and onions are all examples of bulbs which we talked about in our previous article.

Corms are short, stout, enlarged, somewhat flattened underground stems, that store nutrients. The corm itself may be covered with one or more layers of dead foliage leaf bases that are like paper. A stem sprouts from the top of the corm. At the end of the growing season a new corm forms at the base of the first one. Next year’s growth will begin here. Examples are crocus and gladiolus.

Rhizomes are essentially underground stems. They can be thin (think some sod forming grasses) or they can be thick and fleshy. But thick or thin they grow horizontally underground. While growing, they form roots that grow down and send shoots upward. Each rhizome formed is storing nutrients for the new plants. Examples are canna lilies, calla lilies and bearded iris. If you examine bearded iris, you might see that the oldest end is dying off behind as fast as it grows. Plants that reproduce like this can expand forever!

Tubers, thickened, enlarged storage organs, can be formed from a root or a stem. Whether they come from a root or stem, the tubers have a large proportion of tissue that is used for nutrient storage. And we enjoy this storage tissue as an edible treat: potato and yams (stem tubers) and sweet potatoes (root tubers). In your garden you may feast your eyes on tubers such as dahlias and begonias.

So, as you plant this year, see if you can grace your garden with true bulbs, corms, and rhizomes!

If you have questions, call the AgriLife office in Odessa at 498-4071 or in Midland at 686-4700.

Additional information, and our blog for access to past articles, is available at westtexasgardening.org. Click on “Resources”.