Onions: Long Days or Short?

20160408A.jpgThe onion (Allium cepa) is very daylight sensitive. So much so that there are varieties developed especially for the North that require a long photoperiod (14 hours or more of sun per day in the summer) to produce a bulb; in the South, they only produce roots. Most onions offered for gardens in Europe or North America are long-day varieties.

But there are also intermediate-day onions that will form bulbs under days only 12 to 13 hours long, ideal for Southern Europe, North Africa, the Southern US and Central America.

And there are even short-day onions designed for sowing over the winter in mild climates: they only need only 11 to 12 hour days to form bulbs.

Normally Not a Problem, But…

Onion day length needn’t be a concern if you buy your onion seed or onion sets locally. Local merchants sell only varieties adapted to the region. However, if you’re given to buying seeds by mail from exotic locals, be careful. If you buy seeds form a catalog that spans both North and South, it is important to read the description to know for which region the onion is intended.

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.

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