Bulbs, corms and tubers are the specially modified resting stages of certain plants which enable them to live, dormant (e.g. not actively growing), through some adverse climatic condition (usually drought). They all contain a store of concentrated food, and dormant buds, some of which in the bulbs and corms may have embryo flowers already formed inside them, so that when suitable growing conditions recur, the leaves and flowers are produced in a very short time. Because they are not actively growing they can be dug up, transported and sold in shops with little check to the future growth of the plant.
Bulbs contain their food reserve in either special swollen scale-like leaves, loosely packed round the new bud, as in a lily bulb ; or in tightly packed leaf bases encircling the bud, as in daffodil, tulip or onion (allium). In the second type the outside of the bulb is protected by dry, often skin-like, leaf bases. All parts spring from a very flattened stem area known as the ‘plate’, from the underside of which the roots grow.
Bulbous plants are members of either the lily family or the amaryllis family or of the genus Iris.
Corms differ from bulbs in that it is the stem, often flattened, which contains the food reserve. The main bud arises from the center of the upper surface; other buds may often be seen at the sides. Protective scales are dry. Roots form around the edge of the scar of the previous year’s corm.
Each bud is capable of making a new corm and so small cormels arise around the main corm and spread the plant. The plants producing the corms we are considering all belong to the Iris family.
The swollen area of a tuber may arise from a stem or from both root and shoot, but although a stem tuber will produce roots when it starts to grow it is rarely that a root tuber which has lost its shoot (bud) will grow another. Tubers may have scale leaves but more usually lack these. Tubers are not a method of propagation as small ones are not formed from them, as in bulbs and corms.
Tuberous begonias, dahlias and gladiolus are dealt with in the section on Favorite Garden Flowers.
Where to plant the garden flower bulb