If you’ve ever been presented with a “bulb” that looks more like a dirty piece of ginger or a tendrilled potato and wondered if you’ve missed something, this article is for you. I’ll be digging into different types of bulbs and the flowers they produce.
A bulb is a plant’s storage organ. We tend to use the term as a general name for true bulbs, rhizomes, tubers and corms, but there are structural differences between the different types.
Our guide to planting bulbs covers how to plant and care for all types of true bulbs, corms, tubers and rhizomes.
True bulbs
True bulbs are what we typically think of as bulbs: a round, onion-like structure with fleshy scales (modified leaves) and a papery skin. The plant’s shoot is in the very centre, connected to the basal plate (where the roots grow from). You should plant true bulbs tip-up, with the basal plate at the bottom, so the shoot can grow towards the sun.
Daffodils, alliums, hyacinths, fritillaria, lilies, tulips and amaryllis flowers all grow from true bulbs.
Corms
Corms look similar to true bulbs, with a skin and basal plate, but their internal structure differs – instead of layers, a corm is solid inside. This is because it’s technically an enlarged stem. New corms (cormlets) are produced on top of the parent corm, which eventually gets reabsorbed into the soil. You can lift corm clumps in spring and divide them to produce new plants.
Crocuses, crocosmias, freesias, ranunculus, gladioli, Anemone blanda and Crocus sativus (saffron crocus) grow from corms.
Tubers
Unlike bulbs and corms, tubers don’t have a skin. They have a gnarly appearance and can be divided into two categories depending on which part of the plant acts as the food store.
Stem tubers, like potatoes and cyclamen, have multiple “eyes” or nodes from which shoots develop. They tend to grow near the surface, and you can cut them up (as long as each section has a node) to grow multiple plants.
Root tubers, like dahlias and tuberous begonias, are swollen sections of root that typically form in a cluster around the base of a plant’s stem. They have a more elongated shape (like sweet potatoes) and don’t have nodes.
Rhizomes
A rhizome is a section of swollen stem that grows horizontally. Most rhizomes grow underground, near the surface, but a few, such as the bearded iris, sit on top of the soil. Rhizomes have nodes that produce roots and shoots, meaning you can divide and replant them to give the plants more space.
Cannas, lily of the valley, ginger and some types of iris form clumping rhizomes.
Plants with running rhizomes, like bamboo, mint and Japanese anemone, can spread rapidly and be difficult to contain.
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