Califonia Bountiful

Gardening: Surprise packages

Sept./Oct. 2012 California Bountiful magazine

Understanding bulbs, tubers, rhizomes and corms

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Is it a bulb or a tuber, a rhizome or a corm? For gardeners, it's important to know the differences.

Mother Nature plans ahead. Just look at bulbs and their cousins—tubers, rhizomes and corms. I think of them as buried treasures hidden from view for many months. Botanically known as geophytes, these herbaceous plants (ones that die back annually) contain underground storage organs with almost everything needed to grow and bloom another season, with little help from us.

Some grow larger underground each year, producing bigger plants and more blooms. Others use food stored the previous season to emerge and bloom, then as they die back they store nutrients for next year. Still others produce tiny versions of themselves that take several years to mature. Some have such momentum to grow that they sprout and bloom while still on garden center shelves. Lump them all together if you want, but gardeners should know the differences.

Bulbs: These pre-packaged plants wait for opportune conditions to sprout and grow. Leaves, stem, flower and food are packed inside. Many bulbs live from year to year and grow increasingly larger, as well as produce smaller bulbs, or offshoots. Examples include onions, garlic, lilies, tulips and daffodils.

Tubers: A tuber is actually a thickened stem—an underground food storage vessel—and sprouts grow from "eyes." The old tuber is used for food and the plant produces new ones to propagate itself. The most famous "true" tuber is the potato. There are also tuberous roots, including dahlias and tuberous begonias. The begonia tuber differs from other tuberous roots by growing bigger every year rather than renewing itself.

Rhizomes: Like true tubers, rhizomes are thickened stems and appear like long, gnarled fingers. Most—the bearded iris included—prefer to grow flat along the ground with their roots barely covered and their tops exposed to the sun. Like tubers, they have eyes and can be cut in pieces to produce more plants, as long as each piece has an eye. Cannas are another example.

Corms: A corm is a modified stem. It provides all the energy needed for the growing shoot and flower, then new corms form and the process is repeated every year. Gladiolas corms produce tiny corms, called cormels, around the mother corm, and these grow larger until they reach flowering size. Other examples include crocus and bananas.

Pat Rubin





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