Flower “bulbs” come in various forms: true bulbs, corms, tubers, tuberous roots and rhizomes.
To many, this may come as a surprise as often all of the above are popularly referred to as simply “bulbs”. However, what you might think of as a flower bulb may actually not be a bulb at all.
So, does this mean that most of us simply do not know what we are talking about? Not quite! Although the word “bulb” has perhaps no real botanical significance, it is universally accepted practice to refer to all bulbous plants as “bulbs” (bulbous plants being those species of the plant world which produce fleshy storage organs). We at Bulbs & beyond are very pleased with this as it makes our lives a lot easier and simpler!
Below we will describe in summary each form of bulb.
A true bulb is a complete miniature plant (although one could argue that a Hippeastrum/Amaryllis bulb is not exactly miniature). A bulb is made up fleshy scales or rings, with an embryonic flower surrounded by the undeveloped leaves at its centre. The scales are in fact modified leaves that store nutrients to sustain the bulb in its dormant state and early stages of growth. Perennial bulbs add new scales from the inside each year as the outer scales are used up.
Bulbs have a flat bottom part called the basal plate. This basal plate holds together the scales and is where the roots develop and grow. Reproduction of true bulbs is by means of offsets (bulblets), which form part of the basal plate.
Most true bulbs have a papery skin or tunic on the outside. This tunic helps protect the bulb’s tissue from drying out and damage from handling. Some bulbs such as the Lily do not have this protective tunic and are therefore more easily bruised by rough handling, as well as more prone to drying out.
Examples of true bulbs are: Tulip, Hyacinth, Daffodil, Muscari (Grape Hyacinth), Allium and Lily
Some corms may look like true bulbs but their structure is in fact very different. A corm is a swollen underground plant stem, which serves as a nutrient storage organ for the plant to survive its dormant period. Corms have one or more central growing points at the top and a basal node at the bottom from which roots grow. As the plant grows, the corm’s food store is depleted.
Most corms also have a protective tunic formed of remnants of dry leaf bases produced in the previous year.
Reproduction of corms occurs through one or more small new corms developing on the top or at the sides of the old one before it withers away at the end of the growing season. The new corm contains the nutrients for the new dormant plant until it’s time to grow again.
Examples of corms are: Crocus, Gladiolus, Crocosmia, Ixia and Freesia
A tuber is, like a corm, an underground swollen stem that stores nutrients for the plant. It is also designed to provide energy for re-growth during the next growing season. The most famous tuber is the potato.
Tubers have no protective tunic or a basal plate. Tubers generally do not have organised growing points (also called eyes). Some tubers have their eyes at the top but often, new stems can appear from all sides. In fact, it can sometimes be difficult to distinguish the top from the bottom of a tuber. If you are not sure, then the best thing is usually to play it safe and plant it sideways.
Tubers have no specific internal structure like a true bulb and they also don’t make offsets. Most tubers tend to get bigger each year, producing more growing points, but there are some that diminish in size.
Examples of tubers are: Begonia and Anemone.
Tuberous roots are swollen roots that store food for the plant. The tuberous roots are borne as a cluster from the crown (the bottom of a stem). The stem contains the bud (also called eye), which is the new growing point. The fibrous roots absorb water and nutrients from the soil.
A piece of root alone won’t grow or produce a plant. Propagation occurs through cutting off individual roots with a growing bud at the top.
Examples of tuberous roots are: Dahlia and Ranunculus.
A rhizome is a thickened stem containing nutrients to support the plant. Rhizomes differ from other bulbous types by growing sideways rather than up. The stems run completely or partly below the surface of the soil. The main bud (or growing point) is at the tip of the rhizome, but rhizomes branch out, and each new portion forms its own buds on the upper surface or on the sides. Roots develop on the under side of the stems.
Propagating rhizomes is relatively easy by separating them into pieces, with each piece able to give rise to a new plant. However, for a new plant to develop, it is important that each piece has roots and at least one bud.
Examples of rhizomes are: Convallaria Majalis (Lily of the Valley), Canna and Zantedeschia.
For more information or buying flower bulbs online, please visit our website at www.bulbsandbeyond.com