> Next: Bulb Planting Times and Regions
Understanding Bulbs
and Bulblike Plants
A Closer Look at Bulbs
On this page you’ll find information about the main varieties of bulbous plants, including :
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- How to recognize the major types of bulbs
- How true bulbs differ from corms, rhizomes, tubers, and tuberous-rooted plants
- Overview of bulb life cycles including active growth, bloom, reproduction and dormancy
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How Bulbs Differ from Other Plants
The main difference between bulbs and other growing plants is their specialized roots. These unique root systems help them survive periods of drought.
Bulbous plants—true bulbs, corms, rhizomes, tubers, and tuberous roots—store water and nutrients in swollen structures partially buried or beneath the soil.
Trees, shrubs, grasses, and flowers, by contrast, generally have permanent roots that extend down into the soil from a trunk or stalk. Whenever they face heat and drought, they wilt or require extra care to sustain them, while bulbs go dormant and wait for conditions to improve.
Nearby, you’ll find descriptions and a representative sample of each of the different types of bulbous plant and how to identify them by shape.
Skip ahead now, or continue to learn about the typical life cycle all these bulbous plants share in common.
Life Cycles of Bulbs
Most true bulbs and bulbous plants spend part to most of the year inactive, in a dormantlike state. This resting period begins at the onset of dry weather. Their foliage yellows, withers, then dies. After a month or two, the bulb rests in the soil, awaiting rain to trigger new root development and sprouting of foliage and flower spikes.
For evergreen bulbs, dormancy is merely a period of slowed growth. Some tropicals provide year-round, lush-green foliage.
Here’s a typical bulb life cycle.
The onset of rain—or irrigation—causes a stirring within the bulb. As soil moisture penetrates the plant’s tissue, it begins to put down roots.
In cold-winter areas, freezing may interrupt this root growth, which begins again as temperatures moderate. Then, when weather conditions are ideal, a foliage shoot emerges from the bulb, breaking the soil.
In a remarkably short time—sometimes only a few weeks—leaves, stems, buds, and blooms appear. This growth spurt is fueled by the nutrients stored within the bulb. As the bulb is depleted, it either withers entirely, as in the case of corms and some tubers, or shrinks in size. Simultaneously, new offsets are formed, and seeds or bulbils form.
Following bloom, foliage growth continues and supplies nutrients stored for the next year’s growth cycle. Offsets swell in size, and they become independent from their parent bulbs. When the cycle is complete, the bulb rests until new rains fall.
Types of Bulbs
There are five broad horticultural categories of bulbous plants: true bulbs, corms, rhizomes, tubers, and tuberous roots. There are also heat-and-cold sensitive tropical bulbs that may fit within any of the other bulb categories.
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- True Bulb—True bulbs, such as this tulip, have a platelike base of modified stem tissue with attached, scalelike storage leaves and a central growth bud. They are often complete plants, with an embryonic bloom, stem, and leaves. Bulbs have concentric rings when they are cut parallel with their base plate. They regenerate fully each year, often forming small offsets called “bulblets” along their basal plate. They sometimes form seedlike “bulbils” to either the site of their former flowers or, for some lilies, at their axils—where their stems and leaves join.
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- Corm—Corms, such as this crocus, have a swollen, underground stem atop a platelike base with one or more growth buds, usually bearing a flaky, dry, skinlike covering that preserves moisture. Corms appear solid, lacking visible structures inside. They are depleted and wither as the plants grow, and a new corm forms atop the old. Offspring—called “cormels”—form around the base of the new corm, taking 2–4 years to flower if detached and raised separately.
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- Rhizome—Rhizomes, such as this windflower, have a modified and thickened stem that lies flat on the soil surface, are partially buried beneath, or live completely underground. They bear scalelike leaves with latent buds at each axil. Rhizomes branch outward to form new plants, each with independent roots and growth buds, as the parent root withers and dries.
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- Tuber—Depending on species, tubers like the tuberous begonia shown are either modified stems or roots. They lack internal structures, and have tiny surface scales bearing “eyes” (growth buds) along their surface. Tubers usually appear solid when cut. Like corms, many species of tuber shrivel as the plants grow and the nutrients stored within the tuber are consumed; simultaneously, they multiply by division to form new tubers. Others renew and enlarge their tuber each season.
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- Tuberous Root—Bulbous plants with tuberous roots, such as this Persian buttercup, have engorged, fibrous, modified roots surround a crown—the junction of the stem with the root—and bear growth buds. True roots emerge from the tuberous root, and stems, leaves, and flowers sprout from the crown. Over time, multiple crowns emerge from the expanding mass of tuberous roots, creating offspring plants.
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- Tropical bulbs—Tropical bulbs, such as this florist’s amaryllis, frequently are evergreen foliage plants that flower seasonally, but rarely rely on their unique ability to go dormant. Many tropicals grown as foliage plants or for their showy flowers are either true bulbs or are part of one of the other categories of bulbous plants.
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