Every now and then we like to create slightly nerdier blog posts, and now is one of those times. There are those among us who love to know the how and why and all the juicy details — like the difference between bulbs, corms, tubers, and rhizomes. To the casual gardener, these are usually all referred to simply as “bulbs,” but horticulturalists view these types of plants very differently.
The correct umbrella term is actually “geophyte,” which comes from the Greek words for earth (“geo”) and plant (“phyte”). It refers to perennial plants that have underground food storage organs. So aside from knowing the precise terminology, what’s the value in understanding the differences between bulbs, corms, tubers, and rhizomes? They grow differently and have different care needs, and we’re going to show you what those are!
While each of these has general growing and dividing guidelines, plants within the corm category, for example, may have slightly different growing needs, so always be sure to check your particular plant’s requirements before deciding you’re going to dig them up in the fall!
Bulbs
- What they are: The bulb itself is made up of the plant’s immature stem and leaves. The bottom of the bulb is a compacted stem, and roots grow out from this end. The rest of the bulb is like an onion with layers of leaves that surround a bud that grows into the flower above ground. The appearance is round or slightly oblong with a papery outer covering.
- How to grow: After a bulb has been planted and is in place for a few years, they can become overcrowded and stop blooming as much. This is because a bulb grows little baby bulbs around it each year, so it’s a good idea to divide them every 3 years or so. Once the foliage is brown and has died back, you can carefully dig the bulbs up, divide them, and replant (usually in the fall).
- Examples of bulbs: Tulips, daffodils, hyacinth, allium
Corms
- What they are: Corms look similar to bulbs, but their insides are different. Where bulbs have layers of leaves, corms have a solid center. Corms are actually underground stems that sprout and form form flower buds at the top. They’re also round but can have a slightly flat-ish appearance.
- How to grow: At the end of the growing season, a new corm grows at the base of the old one, and next year’s flowers grow from there. So, they are like bulbs in that every few years, they should be divided to continue thriving and blooming well.
- Examples of corms: Cyclamen, gladiolus, snake lily, crocus
Tubers
- What they are: Tubers are underground stems (like potatoes) or roots (think dahlias). Tubers produce “eyes” all over the surfact (again, like potatoes) which grow up through the soil as stems or down into the soil as roots.
- How to grow: Tubers are unique because a gardener can take cuttings from the stem or tuber itself to create new plants. One tuber can produce as many as 6-7 new plants through cuttings, and with each cutting producing several new tubers, you can get 40+ healthy tubers from the original one!
- Examples of tubers: Dahlia, begonia, peony, daylily
Rhizomes
- What they are: Rhizomes look like rough stems that grow out horizontally underground. The bottom grows roots and the top of the rhizome sends up shoots. Buds can form almost anywhere on the rhizome.
- How to grow: The horizontal growth of a rhizome produces new rhizomes or divisions along the sides. You can carefully dig them up and divide them by breaking the pieces or divisions apart, but be sure each division has at least one growing point.
- Examples of rhizomes: Lily-of-the-valley, canna, bearded iris, alstroemeria
