Tubers, Bulbs, Corms and Rhizomes

Yesterday was spent painting - walls, not pictures - so there wasn't much thought given to gardening.  I did get the dahlia tubers and canna rhizomes out of the cold room so I can get them ready to plant in containers within the next week or so.  That will give them a head start so I can enjoy their blossoms for a longer period of time this summer.  I also have gladiolus corms stored in peat moss in the cold room, but those will stay for awhile.

It's confusing to hear about bulbs, tubers, corms, and rhizomes.  And even the experts can't always agree on whether something is a tuber or a rhizome.  They all store the nutrients the plant needs to grow and flower.  They all grow more or less underground and they all get their energy from photosynthesis that occurs through the leaves that are above the surface of the ground.  So, why do we care if it's a tuber or a rhizome? A bulb or a corm?

Well, they often need to be planted differently and they reproduce differently.

Tulips

True bulbs grow in layers and can be peeled off in plates.  They are usually covered with a papery protective layer (a tunic) and the bulb is held together by a basil plate, a flat round disk on the bottom side of the bulb that may have tiny "hair" coming out of it.  Those hair are the beginning of roots.  The center of the bulb is a miniature version of the flower.  True bulbs reproduce by creating offsets, little bulbs that are attached to the larger bulb.  Onions and garlic are true bulbs, as are tulips, daffodils, and amarylis.

 

Gladiolus

Corms look a lot like bulbs on the outside but they are different on the inside. They have the same papery protective covering and a basal plate like the bulb does, but they grow with a solid texture, rather than in layers. The corm is the actual base for the flower stem and as the flower grows, the nutrients in the corm are used up and the corm shrivels.   The corm dies, but only after producing new corms right next to or above the dead corm.  Crocus and gladiolus are two common flowers grown from corms.

"Arabian Nights" dahlia

 A tuber has tough, leathery skin and many eyes, from which the new growth will emerge.  There are many plants that we have commonly called bulbs, which are really tubers.  One that is familiar to everyone is the potato.  Sweet potatoes are also tubers, as are dahlias, begonias, and caladiums.  Tubers are well-behaved in the garden and can be propagated by cutting the tuber into pieces.  Each piece must have at least one eye, preferably two to three, and it will produce a new, identical plant.

Canna

Rhizomes are underground stems that grow horizontally just below the surface of the soil. Rhizomes produce beautiful flowers, but some of them can be pesty.  Rhizomes creep along under the surface of the soil and can spread pretty voraciously.  Cannas, calla lilies, bearded iris and asparagus are well-behaved rhizomes.   Water lilies, lily of the valley, and wild ginger are rhizomes that can take over the world in a very short time if left to grow unchecked. 

And that is probably the best reason to understand the difference between tubers, bulbs, corms and rhizomes.