Bulbs, Rhizomes, Tubers, and Corms: Identification, Planting, and Care

"Bulb" is often used generically, but true bulbs, rhizomes, tubers, and corms differ in structure, growth habit, and care needs. Correct identification ensures proper planting and perennial success.

Structural Differences

Type	Structure	Examples	Food Storage
True Bulb	Central bud + fleshy scales (modified leaves)	Tulip, daffodil, hyacinth, lily, onion	In scales
Rhizome	Horizontal underground stem	Iris, canna, ginger, turmeric, bamboo	In stem
Tuber	Swollen stem tip (no basal plate)	Potato, dahlia, caladium, cyclamen	In stem flesh
Corm	Solid swollen stem base (basal plate)	Gladiolus, crocus, crocosmia, taro	In stem base

Universal Requirements

• Well-drained soil: Rot is the #1 killer. Raised beds/amendments for clay.
• Moisture during growth: Consistent, not soggy.
• Sun per species: Most need full sun; woodland types (bluebells, snowdrops) need dappled shade.
• Foliage ripening: Leave until yellow—feeds next year's storage organ.

Planting Specifics

• True bulbs: Depth 3× height. Point up. Fall for spring bloom; spring for summer.
• Rhizomes: Horizontal, barely covered (iris) or 2–3″ (canna). Fan leaf direction = growth direction.
• Tubers: 4–6″ deep, eyes up. Spring after frost (dahlia, potato).
• Corms: 3–4× height. Point up. Spring (glad) or fall (crocus).

Container Growing

• Pot depth = 3× organ height minimum.
• Well-draining mix + slow-release fertilizer.
• Wire mesh over drainage holes deters squirrels/voles.

Post-Bloom & Dormancy Care

Type	After Bloom	Dormancy Storage
Spring Bulbs	Deadhead; leave foliage 6–8 wks	In ground (most); lift if wet summer
Summer Bulbs (tender)	Fertilize until frost	Lift, dry, store 40–50°F in peat/vermiculite
Rhizomes	Trim fans; divide if crowded	In ground (hardy); lift/store (tender)
Tubers (dahlia)	Cut back after frost	Lift, dry, store cool/dark; pre-sprout spring

Mail-Order Treasures

Specialist nurseries offer varieties unseen in garden centers: species tulips, historic daffodils, exotic arisaemas, rare lilies. Order early (summer for fall bulbs) for best selection.

Know your underground architecture; garden with precision.