One of the fun-yet-frustrating parts of exploring plants and gardening is all the new vocabulary we get to learn. We’ve written several blogs about plant nomenclature and naming and why they matter, but there’s always more out there to explore. So for this blog we’re going to take a look at some of the words we use for plant underground structures: bulbs, rhizomes, corms, and tubers. What are these things? How do they differ from each other and why do those differences matter. Join us as learn the differences between bulbs, rhizomes, corms, and tubers and what those distinctions mean for our gardens. Let’s dig in!
Gardzen Executive Summary:
· Bulbs, rhizomes, corms, and tubers are all underground parts of various plants.
· While they fulfill similar functions, these below-ground stem structures do their jobs in different ways and are structured differently.
· These differences make bulbs, rhizomes, corms, and tubers distinct from each other and help describe how they function in the health and life of the plant.
· By understanding and using these terms correctly, we can better understand our plants and more easily communicate with other gardeners and plant lovers.
The Basics of Bulbs
Let’s start with bulbs, because “bulb” is a common and occasionally misused word and most of us have worked with bulbs either in the garden or the kitchen. Bulbs are essentially a self-contained plant—think of them maybe as a “plant in a box”. The round bulb structure contains the beginnings of all parts of the plant; the roots will grow out of the bottom, the stem and foliage will grow out of the top, and the bulb contains enough stored energy to get the whole thing started. Just add water and soil and you have a plant in fairly short order! Bulbs generally only need to be planted once, and will grow back year after year for the life of the plant (though some may be annuals so we should know what we’re planting!). Common examples of bulbs include tulips, onions, garlic, daffodils, iris, and hyacinths.
While it’s common to use “bulb” to refer to any round underground plant structure, we should try to avoid it and use more specific language. Let’s learn a bit more about that!
What are Rhizomes, Exactly?
Rhizomes are often confused with both bulbs and tubers, but the reality is they’re a different structure that fulfills a different set of functions. A rhizome is an underground section of the plant’s stem. True roots grow out of the rhizome, as do the above-ground parts of the plant. Rhizomes are swollen, fleshy, and are part of the plants energy and nutrient storage system. Rhizomes grow parallel to the surface of the ground, and produce new buds or eyes that expand outward to become both new parts of rhizome and by extension new above-ground parts of the plant. Older parts of the rhizome don’t produce above-ground growth.
Examples of rhizome producing plants are ginger and turmeric—the rhizome is the part we harvest for food—and ornamental plants like bearded iris, Canna lilies, and Chinese lantern (Alkekengi officinarium, formerly Physalis alkekengi).
How do Corms Differ from Roots and Rhizomes?
OK, corms are a lot like rhizomes in that they are swollen, below-ground sections of the stem that are shaped much like a bulb. Corms grow out of a section of the roots called the corm cortex, and they form a dry outer tunic or protective layer made of leaves and stem layers produced in previous years. Like rhizomes, new corms grow out of the old one, generally forming from the top section. Cormels—little baby corms that can become their own plants—sometimes form out of the base of a corm.
While the word “corm” is used less frequently than bulb or even rhizome, some popular garden plants have corms including Gladiolus, giant taro, and many members of the Asteracea or daisy family.
And Finally: What are Tubers?
Bear with us, please: tubers are . . . sections of the plant’s stem that grow underground and are swollen in order to store nutrients. What distinguishes tubers from rhizomes or corms is that while tubers have roots growing from their surface and growth buds growing upward out of them to become the above-ground sections of the plant, tubers produce growth buds all over their surface and the tuber itself can be cut into pieces and replanted. As long as each cut piece has a growth bud (also called an “eye”), the new piece can grow into a new plant.
Potatoes are probably the most popular tuber plant in most of the US and Canada, but dahlias are also grown from tubers, as are begonias and anemones.
Why Underground Plant Structures Matter
We know this may be a bit confusing. It feels like we’re splitting hair in some places, and maybe in some ways we are. However, by knowing the right terminology and using it correctly, we can enhance our own understanding of how plants grow and how the specific parts of each plant work. We can also communicate more effectively with other gardeners and better understand books, articles, blogs, and videos about gardening. So thank you for joining us on this journey and learning with us as we discovered the differences between bulbs, rhizomes, corms, and tubers. If you have any questions—or if we got something wrong—please reach out in the comments or via email. Gardzen is all about community and we love to hear from you!
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