Bulbs Garden Myths

Mini Horticultural Myth: Dormant Bulbs Need Darkness

Sleeping bulbs are indifferent to light. Ill.: owips.com, http://www.mycutegraphics.com & http://www.wpclipart.com, montage: laidbackgardener.com

I want to bring up a very minor detail on the cultivation of tender bulbs (gladioli, cannas, dahlias, tuberous begonias, etc.), but one still worth clarifying: the concept that bulbs need darkness during their dormant period.

Typically, the explanation offered to gardeners is that when you bring tender bulbs indoors, you need keep them in a spot that is cool, dry and dark, such as a basement, a slightly heated garage or a root cellar. But in fact, darkness itself is not a factor.

When a Bulb Is Sleeping

As long as you keep dormant bulbs dry (and, for many, cool as well), they don’t care about the lighting conditions. Photo: http://www.dutchgrown.com

Dormant bulbs are just that: dormant. They’ve stopped all growth. And when they’re in that state, they’re perfectly indifferent to light. Sun, partial shade, darkness: it’s all the same to them. True enough, you don’t want to store them in a spot that gets really hot as that could cause them to dry out and intense sun can indeed heat things up quite a bit. However, if you have potential storage space that receives light part of the day or even all day, yet remains cool, that would be a perfect place for bulbs.

Other Dormant Plants Too

Also, the same information applies to any plant that goes dormant at some time during the year: amaryllis, cyclamens, desert cacti, etc. Yes, do stop watering them and yes, do put them in a cooler place … but there is no need to keep them in the dark unless there is some reason that would be convenient for you.

I tried to come up with even one exception: a single plant that must necessarily experience darkness 24 hours a day for a long time when it is dormant, but I couldn’t think of one.

And, when you think this over, this is quite logical: when a plant goes dormant in the wild, it doesn’t dig itself up and take refuge in a dark cave nearby. It stays where it is and puts up with whatever natural light is found in that spot.

So, if there is a window in the garage or basement where you overwinter your bulbs, you don’t need to block it nor to seal the bulbs in an opaque box. As long as this light doesn’t overly heat the room, its presence or absence is irrelevant.

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

1 comment on “Mini Horticultural Myth: Dormant Bulbs Need Darkness

  1. I didn’t give it any thought. Most of our bulbs stay in the ground all year, but those that got dug were stored in mesh bags hung in the barn. That is how I always did it. While growing certain bulbs in pot, there were a few that were grown initially in dark, just to stretch them. They certainly did not need it. It was done merely for better stems.

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