What is a Flower Bulb and What is Not

The only thing rhizomes, corms and tubers have in common with a flower bulb is the fact that they are all
geophytes, the part of the plant that stores food and water. A bulb contains a miniature version of the plant to be. Cut it open and there is the fully-formed bud and leaves you will see when the plant blooms.
None of the other have this characteristic.

Corms actually look a lot like a bulb- on the outside, that is. The corm is the base of the flower stem. The flower grows outside of the corm, not inside like in the bulb. Also, the corm dies as the plant grows. New corms are formed to produce the next years flowers. Bulbs do not die. They produce flowers year after year. With corms, it can take years for the flowers to reach blooming size.

Tubers look nothing like a bulb or a corm. Think potato. Tubers develop eyes on the skin. These send out shoots that become the above the ground part of the plant. If you cut a potato into sections where each section has one eye, each section will become a new plant. Unlike bulbs, the plant does not develop inside of a tuber.

Rhizomes are nothing like bulbs at all. They are not even the same shape. They are underground stems. Bulbs grow vertically. Rhizomes grow horizontally. The grow under ground and send up new plants along the way.

Each one is a completely different, and very complex, growing mechanism. It may not seem to be a big deal, but gardening is more than putting the plant in the ground and letting it grow. Each one needs a different type of care. Each one reproduces in a different way. To propagate the plants you need to know how the specific one grows.

In order to get the most out of your garden, do your homework first. Find out what type the flowers you want are. Find out how they grow and what special care they need. For instance, some flower bulbs should be brought inside during the winter in certain areas and replanted again in the spring.

It is a wise gardener who realizes that there is always something new to be learned from the plant world and learning by research is much better than learning by doing things the wrong way.

Sources:

UC Davis

Planting Flower Bulbs