What is a Bulb Plant?

True Bulbs

• True bulbs produce plants such as the giant flowering onion (Allium giganteum) from the amaryllis family for U.S. Department of Agriculture hardiness zone 5, and is actually a complete plant in a tiny package. Fleshy scales surround the future plant protecting necessary food for the plant to grow. After a bulb has bloomed into a plant, the leaves manufacture food the next year and transfer it underground to start the chain again. As a bulb grows, it produces tiny bulblets, which you can remove to grow as new plants.

Corms

• Another type of plant producing bulb is simply a modified, swollen stem filled with food-storage tissue. A corm usually is short and squat and covered with a mesh-like material. Growth eyes appear at the top. Corms disappear after the plant develops and new one form for next year's growth. Some corms also produce cormels, which are similar to bulblets. An example of a plant producing corm is a crocus (Crocus) suitable for USDA zone 4,

Rhizomes

• Rhizomes produce plants from a bulb-type system consisting of a thick food-storage stem that grows along the soil's surface. Growth buds form on a rhizome for the next season's leaves and flowers. Bearded irises (Iris germanica) grow from a rhizome and are well suited for various zones, depending on the cultivar. The Calla lily (Zantedeschia aethiopica), suited for USDA zones 8 through 10, is also a rhizome.

Tubers and Tuberous Roots

• Tubers, such as the winter aconite (Eranthis hyemalis) (See reference 2, “Winter Aconite – Eranthis hyemalis”) for USDA zone 4, have one or more underground, non-creeping food-storing stems that are thick and fleshy. These plant producing bulbs can be dug up and stored over winter. Tubers have scattered buds along the surface of the fleshy root which develop into new plants. The common potato is a tuber. Tuberous roots are a form of bulb, but are actually thickened roots. An example of a tuberous root is the Grecian windflower (Anemone blanda) suited to USDA zone 6.