We’ve talked alot about plants and their care this season. From floating root systems to non-flowering greenery to tuberous roots. Wait. What?! If you’re thinking ‘What’s a tuberous root?’ you’re not alone. Getting some clarity on the subject can actually make the care of these plants much easier. Have a read as we glance at bulbs, tubers, corms, and tuberous roots and what makes them….grow.

Diving right in: Tuberous roots are made of root tissue. Tubers are made of stem tissue. This is simple to visualize if you’re like us and have been getting your hands dirty planting and trimming these plants for a number of years. Both tissue forms store food and energy that helps plants survive during the winter or dry months.

Dirty Details: Tubers come in two types: stem or tuberous root. Stem tubers are formed from rhizomes. Shoots are produced on the top sides of the stem tuber that later grow into stems and leaves. The undersides of stem tubers produce roots.
Tuberous roots are also referred to as storage roots and are a lateral root that enlarges to function as a storage organ. The enlarged area of the tuberous root may form at the end of the root or the middle, or it may encompass the entire root. Potatoes are a tuberous root, while begonias are stem tubers.



You are already familiar with a popular tuber: the potato. Other tubers include tuberous begonia and cyclamen.

Tubers have these features:

  • Tubers have no tunic. No papery cover surrounding it.

  • Tubers lack a basal plate. Most tubers root from the bottom.

  • Tubers have several growing points, called eyes. More organized tubers, such as caladiums or tuberous begonias, have their eyes at the top. Some tubers, such as anemones, aren’t so orderly. Distinguishing the top from the bottom of the tuber may be difficult. If you’re not sure, plant it sideways and let the tuber figure out which direction to grow.

  • Tubers are made of modified, undifferentiated stem or enlarged hypocotyl tissue. They have no highly specific internal structure.

  • Tubers don’t make offsets or produce new tubers. Tubers usually just get bigger each year, making more growing points.

Tuberous roots


Tuberous roots are modified, enlarged, specialized roots that store food, and are used up during the growing season to be replaced by new storage units.
The tuberous roots cluster together, joined to the bottom of a stem.
The stem contains the new growing point for the next year — a piece of root alone won’t grow.

Examples of tuberous roots are: dahlias, daylilies, and sweet potatoes.




Rhizomes are stems that grow sideways rather than up, running along the surface of the soil or just below it.
Plants that use rhizomes for food storage have fatter, more bulb-like rhizomes, covered with a dry base of leaves. Rhizomes branch out, and each new portion develops roots and a shoot of its own, making them natural propagators.

Familiar rhizomes include: iris, water lilies, lily of the valley, canna, and ginger (Zingiber officinale).



Most of our aquatic favorites fall into the rhizome category such as Canna, Water Lilies, Arrowhead, Corkscrew Rush, and Iris.

And because it’s bulb season, we’ll take a look at a ‘true’ bulb versus a corm….

True bulbs


True bulbs, such as daffodils, tulips, hyacinths, and snowdrops, often have a papery skin or tunic on the outside, much like an onion.
Bulbs with a papery covering are called tunicate bulbs.
The tunic helps protect the bulb from drying out when it’s resting or waiting to be planted.
However, some true bulbs, such as lilies, don’t have a tunic. These bulbs dry out faster and are more easily bruised.

All true bulbs share the following characteristics:

  • They’re more or less rounded, sort of ball-like, and narrow to a point on the top. Leaves and flower stems appear from this point.

  • With or without a tunic, true bulbs have a flat part, called a basal plate, at the bottom. That’s where roots grow and also where shoots and scales are attached.

  • True bulbs have new bulbs, called offsets, which form from the basal plate. When they get big enough, these offsets, or daughter bulbs, produce flowers on their own.

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  • True bulbs are made up of rings, called scales, which are modified leaves that store food. Cut apart a true bulb, such as a hyacinth, at the right time of year, and you can find a miniature flower inside, just waiting to begin growing. Perennial true bulbs add new rings each year, from the inside. Old rings on the outside are used up, but the true bulb itself persists from year to year.



If any of the characteristics that identify true bulbs are missing, the plant isn’t a true bulb. Instead, it’s a corm, tuber, tuberous root, or rhizome.

Popular corms include: crocosmia, gladiolus, freesia, and crocus.

Corms have these traits:

  • Corms have a tunic. The tunic may be fibrous, what botanists call netted or reticulate, or the tunic may be smoother, with distinct rings, what botanists call annulate. Some crocuses have reticulate tunics, and others are annulate, which is one way you can tell crocus species apart.

  • Corms have a basal plate at the bottom and one or more growing points at the top. Bulbs and corms both have a definite vertical orientation.

  • Corms are undifferentiated, uniform, and contain no rings when cut apart. Corms are stem tissue, modified and developed to store food.

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  • The corm you plant is used up for growing the flower. Before it withers away at the end of the growing season, however, a brand new corm (sometimes several new corms) forms and replaces the mother corm. The new corm contains the food reserve for the dormant crocus or gladiolus until it’s time to grow again.

    Thanks to our source for such great planting information!