Gardeners refer to several distinct plant structures as flower bulbs in everyday conversation.

• True bulbs – Rounded, with a pointed top and a flat base where roots grow: Allium, Anemone, Bluebell, Daffodil, Hyacinth, Snowdrop, Lily, Tulip
• Corms – Similar to bulbs, with buds on top and roots from the base: Crocus, Gladioli
• Tubers – Swollen roots like Dahlia, or swollen stem bases: Cyclamen, Aconite
• Rhizomes – Horizontal, swollen stems, growing on or just below the soil: Bearded Irises, Lily-of-the-valley, Cannas

From a planting season perspective, bulbs / corms / tubers / rhizomes are handled one of 4 ways:

• Dry, dormant bulbs are planted in Autumn
• A limited range of bulbs are planted in growth (In the Green), in early Spring
• Tender species like Dahlias are best planted into warm soil in late Spring
• Some late season bulbs like Nerines and Colchicums can be planted until the end of Summer

For convenience, flower bulbs are commonly classified as Spring or Summer flowering.