Getting to the Tuberous Root of the Matter
Botanists like to make things complicated. Because of this, an almond is not really a nut but a drupe, and watermelons are actually berries. (Look it up if you don’t believe me.) Similarly, not all things we think of as bulbs are really bulbs. They may be corms, rhizomes, tubers, or tuberous roots.
This wouldn’t matter except for the risk of botanical humiliation. Say you are at a dinner party and you boast about the hundreds of crocus bulbs you planted. “They’re actually corms, not bulbs,” someone says, a patronizing smile playing upon their lips.
At this point you have several choices. You can pretend you meant to say corms all along. You can try to create a diversion by knocking over someone’s glass of wine. Or you can demand satisfaction for this insult: weed whackers at dawn.
Better you should minimize the risk of violence and emotional trauma by getting clear on your bulbous structures.
This topic is on my mind because I just started a class at the Chicago Botanic Garden on hardy bulbs (and corms, etc.). The other night this subject was explained and I feel inspired to share my enlightenment with you. You’re welcome.
But before we get started I also want to share an amazing bulb fact. Did you know that if you plant bulbs at a less than ideal depth, the bulbs themselves will move to the spot they like best? They do this with contractile roots, which pull the bulbs through the soil. Don’t know about you, but that makes me feel so much better.
And now for the bulbous structures.
True bulbs. True bulbs are like miniature plants – if you cut them open, you’ll see a bud, stem, and foliage at the center. The bud is surrounded by scales that hold stored energy, and sometimes a papery tunic. The scales are held together by a basal plate. Tulips, daffodils, hyacinths, scillas, snowdrops, lilies, and alliums are all true bulbs.
Corms. Corms are hunks of stem tissue connected to a basal plate. The tissue is just tissue – a cross section will show no rings or parts. Roots grow from the basal plate. Corms live for only one year, but they replace themselves energetically. Crocus, crocosmia, gladiolus, colchicums, and erythroniums are corms.
Tubers. Like corms, tubers are hunks of stem tissue. Unlike corms, tubers are perennial. The stem portions sprout eyes and roots. Potatoes are tubers, of course, as are anemones and corydalis.
Tuberous roots. Like tubers except the mass is made of root tissue instead of stem tissue. How do we know? Stem cells have little bundles of vascular tissues around the periphery, root cells have vascular tissues in a central core. Got that? Me neither, but just say it with confidence while looking people straight in the eye. Dahlias, sweet potatoes, and eremerus have tuberous roots.
Rhizomes. Rhizomes are horizontal stems growing on or just below the surface. Important note: “horizontal” means you don’t plant rhizomes pointing down, which is something I did for years. Rhizomes include bearded iris, trillium, Solomon’s seal, hardy geranium, and canna lily.
So. Now you can amaze your friends at parties with your knowledge of bulbs and bulb-like plants. They may be edging away from you, but they will be amazed.