Bulbs, Tubers, Corms, and Rhizomes

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

Learning what’s going on under the soil and where your houseplant began its life can help us gain a better understanding of how to care for our plants. Let’s dig into that curiosity and discover where our plants begin their journey!

Bulbs, tubers, rhizomes, and corms are often collectively referred to as “bulbs" as their basic functions serve similar purposes: 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.

Bulbs

True Bulbs are globe shaped with papery skin and made up of modified leaves that store nutrients and enclose around a vegetative growth point or flowering bud. Onions and amaryllis may be the most visually clear examples of true bulbs.

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

Corms

Corms look like true bulbs but are actually swollen base stems that store food for the plant during dormancy. Unlike true bulbs, corms are solid and often elongated in shape with a membranous or scaly texture. If you've ever dug up your oxalis triangularis or looked closely at turmeric, these have the quintessential qualities of a corm.

Examples of corms include: alocasia, elephant garlic, oxalis, crocus, freesia, gladiolas, tuberous begonias, saffron crocus, water chestnut, ranunculus and celeriac just to name a few!

Tubers

The first way to differentiate between a corm, a true bulb and a tuber is this: tubers do not grow an outer skin. Tubers can be further divided based on the location of their food storage unit: root or stem.

Root tubers are modified nutrient storages areas often growing in clusters near the base of the stem (think dahlia or sweet potato). These growth structures lack nodes or "eyes" as well.

Stem tubers generally form just below the surface of the soil. They have several nodes or “eyes” all over which can develop into new plants (think potatoes). Examples of stem tubers: yams, cyclamens, potatoes, Jerusalem artichoke aka sunchoke or earth apple, anemone and caladium.

Have you ever see a green skinned potato? That's what can happen when stem tubers get too close to the surface, they'll begin to produce chlorophyll when exposed to sunlight, just like leaves of our plants!

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. 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 as that generally indicates it is reproducing on its own rhizome, away from the mother plant.

Examples of above ground rhizomes: rabbits foot ferns and bearded iris.

Stolons

A stolon is an above-the-ground shoot or stem that creeps along the surface of the soil and 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 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 shoots that grow along the sides or base or trees, shrubs or in the case of bananas, herbs! They are generally found popping up away from the the mother plant and are 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. Examples of offsets include: aloe vera, bromeliads and air plants, hens and chicks, haworthia 

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