Confusion Over Hardiness Zones

‘Sensation’ (Syringa vulgaris ‘Sensation’) is actually a very hardy lilac, fully capable of growing in hardiness zone 5. Photo:

Question: I just bought a ‘Sensation’ lilac, but I forgot to look at the hardiness zone. So here I am with a lilac from zone 3 while I live in zone 5. What will happen? Did I just throw money out the window? Which lilac is more suitable for zone 5?

Annie Bilodeau

Answer: You’ve misunderstood how hardiness zones work.

When some nurseries put only one hardiness zone on a plant label, in this case, zone 3, that was not meant to exclude all the other zones. You’re supposed to understand that the zone given is the coldest one the plant can support, but the plant will also grow in warmer zones. It is the minimum zone the plant can tolerate.

In the case of your lilac, it’s capable to tolerating quite serious cold, down to -40ºF/-40ºC, but will also do fine in milder climates, like your zone 5, where winter temperatures are much warmer. Check the table to better understand.

Now, this confusion would have been avoided if the label provider had given the range of hardiness zones the plant is adapted to … and many nurseries do. In the case of your ‘Sensation’ lilac, for example, as a cultivar of the common lilac (Syringa vulgaris), that would be zones 3 to 7 (common lilacs need a cold winter and won’t readily bloom in milder climates, that is zone 8 and up). As you can see, zone 5 is safely ensconced in the middle of the lilac’s cold tolerance range.

So, when you shop plants and see only one zone on the label, keep in mind that you can buy plants from your hardiness zone (5), but also plants tolerant of greater cold (zones 1 to 4 in your case). So, 1, 2, 3, 4 and 5 are the ones you can choose. It’s those from zones warmer than your own (6 to 13) you need to avoid, as they won’t tolerate the colder winters in your area.

💡Helpful Hint: If ever you’re not sure of whether a plant is hardy where you live, why not ask someone from the nursery staff? They’ll be able to direct you to plants that will grow well in your area. 

To answer your second question, “Which lilac is more suitable for zone 5?”, almost all lilacs are hardy in zone 5, so you could pretty much take your pick.

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.

3 comments on “Confusion Over Hardiness Zones

  1. Incidentally, when we grew French hybrid lilacs, like ‘Purple Sensation’, they were supposedly less reliant on chill to bloom well. However, even the common lilac blooms quite well here, and in climates with even less chill. They really do not seem to require much chill at all, which is why they are not prescribed a range of hardiness zones.

  2. I would like a lilacs, but being in zone 8, I am never sure they would bloom.

    • Yes, zone 8 is not usually ideal for lilacs, but if “your” zone 8 has a distinctly cooler winter, you might want to try one to see.

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