bulbforming

Bulbforming is a plant growth habit in which perennials, known as geophytes, survive from year to year by producing underground storage organs called bulbs. These bulbs store nutrients and energy, allowing the plant to endure unfavorable seasons such as drought or cold. When conditions improve, new shoots and leaves emerge from the bulb, followed by flowers.

A true bulb consists of a short basal plate with fleshy storage leaves arranged in layers, often surrounded by a protective outer coat. Some bulbs are tunicate, having a papery outer tunic, while others are composed of loose scales without a distinct tunic. Bulbs are distinct from other underground storage forms such as corms, rhizomes, and tubers, which have different structural arrangements and modes of growth.

Bulbs reproduce vegetatively through offsets—daughter bulbs that form at the base of the parent bulb—facilitating clonal spread. They can also produce seeds, but many cultivated bulbs are propagated by dividing offsets. The bulb habit generally favors plants adapted to seasonal climates, with a period of dormancy followed by renewed growth.

Common examples of bulb-forming plants include members of the Amaryllidaceae and Liliaceae families, such as daffodils (Narcissus), tulips (Tulipa), crocuses (Crocus), onions (Allium), and lilies (Lilium). In cultivation, bulb-forming species require well-drained soil, appropriate burial depth, and, for many species, a chilling period to induce flowering.