Digging a hole for a crocus bulb with a trowel

Bulb types explained

Confused by corms, rhizomes and tubers? We explain the differences between them.

Bulbs are some of the easiest and most rewarding plants to grow – they can provide weeks of colour in the garden for just a little effort, lighting up pots and borders. Many popular garden plants are grown from bulbs, including daffodils, tulips, bluebells, lilies, gladioli and canna lilies.

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Discover 10 of the best bulbs for pots.

A bulb is an underground food storage organ from which shoots appear when the bulb comes out of its dormant phase. The term ‘bulb’ not only refers to ‘true bulbs’, such as daffodils but also corms, rhizomes and tubers.

There are two main planting times for bulbs. Spring-flowering bulbs, such as daffodils, tulips, crocus and bluebells are planted in autumn; they then die back and go dormant in summer. Summer-flowering bulbs, such as dahlias, lilies, gladioli, are planted in late spring; they go dormant in winter. Some bulbs, such as hyacinths can be ‘forced’ to flower earlier than they would normally.

Most kinds of bulbs are planted in the same way – at two or three times their depth, in well-drained soil or gritty compost. There are a few key differences, however. Find out more about the different types of bulb, below.

The term 'bulb' not only refers to 'true bulbs', such as daffodils but also corms, rhizomes and tubers.

True bulbs

Handful of tulip bulbs
Handful of tulip bulbs

A true bulb, such as an onion, consists of fleshy layers of scales, which are leaves in their embryonic state that store food for the developing plant and protect the stem and flower at the centre of the bulb. They often have papery skins, called tunics. Examples of true bulbs include daffodils, tulips, alliums and garlic. They are generally planted at two or three times their depth.

Lily bulbs don’t have a tunic, so the scales are exposed. These scales can be snapped off, put in a bag with damp, gritty compost, somewhere warm, and new bulblets will develop.

When planting bulbs, it’s important to get the base pointing downwards, so the roots can grow down and the shoot can grow upwards towards the light.


Corms

Digging a hole for a crocus bulb with a trowel
Digging a hole for a crocus bulb with a trowel

Corms are enlarged stems in which food is stored. It has a basal plate, tunic and growing point. They look similar to bulbs but if you cut one in half, you’ll see that it’s a solid mass, rather than concentric rings of leaves. Crocosmia, crocus, freesia, ranunculus, grape hyacinths, anemones, autumn crocus, Oxalis triangularis and bananas all grow from corms.

Small corms can be planted at about 5cm deep. Clumps of corms can be dug up in spring and the individual corms replanted to develop into new plants.


Rhizomes

Iris rhizomes
Iris rhizomes

Rhizomes are swollen underground stems that store food. They usually grow horizontally near the soil surface. Ginger lilies, cannas and many irises are grown from rhizomes. They have several buds along them and can be divided when they become congested – find out how to divide bearded irises.


Tubers

Dahlia tubers carried in a blue crate
Dahlia tubers carried in a blue crate

Tubers are swollen stems or roots that are food stores. Dahlias, cyclamen, tuberous begoniaszantedeschia and Anenome blanda grow from tubers; potatoes are actually stem tubers. Shoots develop from the buds or ‘eyes’ and you can get several plants from one tuber by cutting it into sections – each piece will develop into a mature plant as long as it has at least one eye.


What’s in a bulb?

A growing bulb sliced longitudinally, with its parts labelled 1-4
A growing bulb sliced longitudinally, with its parts labelled 1-4
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  • 1: the leaves use sunlight to make energy, which is stored in the bulb for next year’s display
  • 2: these fleshy scales are where the bulb stores energy
  • 3: the basal plate is where roots grow from – ensure it points down when planting
  • 4: the roots absorb moisture from the surrounding soil and anchor the bulb in place

Layering bulbs in pots

Layering bulbs in pots is a great way of enjoying colour for many weeks in spring. Watch our video guide to layering spring bulbs in a pot, using crocuses, daffodils and tulips.

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