Bulbs, Tubers, Corms, and Rhizomes

It's a bulb, right? Or wait, it's a corm! What is a rhizome exactly?

I thought I knew the answers to these until I began researching and this seems like an overlooked part of plant parenting, something we skip with all the excitement of acquiring a new plant.

Learning what’s going on under the soil and how our plants begin their lives can help us understand how to better care for our plants. So let’s dig in to discover where our plants begin their journey!

Seeds, we all know about them! The incredible triumph of seeds, teeny tiny embryos, potential life of flowering plants or trees. Simply incredible! 

Bulbs, tubers, rhizomes, and corms however are often collectively referred to as “bulbs”. Why? Basically their functions serve a similar purpose: to store food, water, and minerals as energy and to give new life to the plant. Plus, they often look the same or have similar physical attributes. But there are differences and being able to identify and recognize them can help us grow into wiser plant parents and better gardeners too. 

Bulbs

True Bulbs are globe shaped, modified leaves that enclose a bud and store nutrients. Often confuses with or grouped with corms which are solid inside, whereas bulbs are soft.

 Horticulturalists call these true bulbs to differentiate them from the all the other types. True bulbs consist of layers of modified leaves and contain a miniature flower or sprout in the center.

Examples of true bulbs include onion, garlic, amaryllis, shallots, tulips, daffodils and lilies.

Corms

Corms look like true bulbs but are actually swollen base stems that store food for the plant during dormancy. Corms are solid, unlike true bulbs, and generally elongated looking bulbs with a membranous or scaly texture. If you've ever dug up your oxalis triangularis or looked closely at turmeric, you can imagine the look and feel of a corm.

 When the parent corm is old and has given all its energy, it’s then reabsorbed into the soil, leaving behind cormlets or cormels that form at the base of the shoot, just below the old corm. They begin absorbing and storing nutrients (you can occasionally spot old corms attached to new ones if you look closely). This form of vegetative reproduction allows corm type plants to be divided and spread out easily. Oxalis (or sour grass) is a good example of this process. When grown in its native habitat it can easily spread and take over a patch of land! 

Examples of corms include: alocasia, elephant garlic (actually a leek), oxalis, fritillaria, colocasia (taro), crocus, freesia, gladiolas, tuberous begonias, saffron crocus, water chestnut, celeriac just to name a few!

Tuber

There are two types of tuber: root and stem. The main difference between root and stem tuber is where the tuber is located on the plant. Root tubers are swollen area, a modified lateral root, enlarged to function as a storage organ, whereas stem tubers are, you guessed it, swollen stem roots!

Stem tubers generally form near the surface of the soil. They have several nodes or “eyes” that develop into new plants (potatoes are probably what comes to mind). Have you ever see a green skinned potato? That's what can happen when stem tubers get too close to the surface, they'll produce chlorophyll when exposed to sunlight.

Examples of stem tubers: yams, cyclamens, potatoes, Jerusalem artichoke aka sunchoke or earth apple, anemone, begonia, ranunculus, caladium.

Root tubers aka root crops also perform the general function of roots. They absorb and store water and minerals and they anchor the plant body to the soil. Root tubers are able to reproduce as they have minute scale leaves bearing buds that can potentially produce a new baby plant.

Examples of root tubers: carrots, sweet potato, cassava, dahlia, beet, parsnips, turnips and radishes

Rhizomes

Rhizomes are a horizontally growing, modified stem capable of producing both the vegetative shoots and roots. The word "rhizome" means “mass of roots" in Greek, which is helpful in identifying a rhizome but they differ in size and shape and can grow both above and below ground. However all rhizomes perform the same function: to store starches and proteins to enable plants to survive harsh weather conditions underground, like freezing wintertime temps!

Rhizmones can both run or stay compact, another tricky feature for identification.  Dense rhizomes like ginger or clumping bamboo have short internodes and form compact, dense clumps that don’t spread. Running rhizomes such as mint or horsetail have longer internodes and spread quickly in a horizontal or lateral growth pattern, making them more difficult to control and therefore can become invasive.

Anyone who has grown mint or bamboo knows how they can take off running! Some rhizomes, like horsetail, bamboo, mint, or Bermuda grass can multiple quickly and do become invasive. Sometimes that's what you want to fill an empty garden or landscape, but sometimes it can get out of control! Knowing which plants spread by rhizomes helps us to avoid plants that might be vigorous growers for your garden, landscape, or even inside your houseplant pot!

Rhizomes can be propagated by dividing into sections, just be sure each section has an "eye" or "button" which is the node where new roots and leaves will emerge.

Examples of below ground rhizomes: Boston fern, Snake plant, Venus fly trap, peony, turmeric, ginger, running bamboo, calla, banana, horsetail, asparagus, canna lily, zz plant, stinging nettle, rhubarb, mint, and Japanese knotweed.

*Carnivorous plant fun fact: a mature Venus fly trap plant can be divided once it has at least seven leaves. That indicates its reproducing on its own rhizome, away from the mother plant.

Above ground rhizomes include rabbits foot ferns and bearded iris.

Propagation

Stolons

A stolon is an above-the-ground shoot or stem that creeps along the surface of the soil. Stolons have the potential to grow a clone of the original plant once rooted. That clone, once established, can live as its own independent plant and send out new runners, repeating the cycle. Stolons don't store nutrients like bulbs, tubers, corms, and rhizomes hence their size and shape are generally thinner.

Examples of stolons are spider plants, strawberry plants, and many grasses (especially warm weather grasses).

Suckers

Did you know banana plants are the largest herbaceous flowering plant on earth? Bananas can reproduce through their rhizome, but also via something called a sucker. Suckers are side shoots or a root sprout generally popping up away from the mother plant and capable of living independently once established. A sucker is genetically identical to the mama plant.

Offset

An offset or a "pup" is similar to a sucker except for the location of where it grows. Offsets grow from a bud at the base of the mother plant and is genetically identical to her. Examples of offset reproduction can been seen in many succulent type plants, aloe vera, bromeliads and air plants, hens and chicks, and haworthia are perhaps the most common.

Hope this blog posts inspires and guides you to a greater understanding of growing your houseplants and garden holistically!

Sending love, Karina and Team SE