Understanding Your Flowers: The Five Types of Bulb Structures

Bulbs are among the most beautiful, interesting, and easy-to-grow flowers. Though not as prized as in 17th-century Holland, they’re still loved for scent, color, shape, and hardiness. Popular bulb-grown flowers include tulips, crocuses, daffodils, irises, lilies, daylilies, dahlias, and snowdrops.

All grow from underground nutrient-storing structures. Collectively called “bulbs,” there are five distinct types:

True Bulb

Underground stem base with embryonic plant (leaves, stems, flower buds). Surrounded by overlapping scales; basal plate produces roots. Examples: daffodils, tulips, lilies. Handle carefully—susceptible to dryness. Can live years unplanted.

Corm

Solid stem base, no scales. Roots from basal plate; growth point at top. Examples: gladiolus, crocus. Lasts one season; new corm forms atop old; cormels at base.

Tuber

Underground stem base, no basal plate. Roots from base and sides; multiple growth points on top.

Rhizome

Thickened stem growing partly/wholly underground. Main growth point at one end; others along sides. Best known: bearded iris.

Tuberous Root

Not a true stem; fibrous roots from sides and tip. Swollen parts radiate from center. Growth points on old stem bases. Examples: dahlias, daylilies.

Knowing these structures helps you plant, care for, and propagate each correctly.