How Do You Know If A Plant Is Hardy?

– Posted in: FAQ, Plant info
19 comments

I was just reading Graham Rice’s musings on plants that grow in the coldest climates. He observed that the resources he consulted did not agree on which plants were tough enough to take USDA zone 2. If you’ve been gardening for any length of time (which of course Graham has), this won’t surprise you.

First, there is the matter of statistics. The fewer people gardening in a certain zone, the less data available on any particular plant. I imagine with a lot of plants, to say it’s hardy to zone 2 is as much an educated guess as it is a tested hypothesis.

And then there are so many factors affecting plant hardiness besides air temperature that some people think the whole concept of hardiness zones is a joke. Ellen Hornig of Seneca Hill Perennials admits, “We include hardiness zones largely to pander to popular prejudice and give you a small degree of guidance.” Tony Avent provides a detailed analysis of the problems inherent in the concept of hardiness zones.

But you’ve got to start somewhere. That’s where other local gardeners are a tremendous help. If anyone is going to know what will make it in your garden, it’s someone with the same growing conditions. And many people who are still too isolated to find a local garden buddy now have the benefit of internet access, and can consult and befriend others in similar conditions.

image of dead caryopteris

This caryopteris was a gamble that I lost. It failed to return after its first winter.


In the end, the only one who’s an expert on what grows in your garden is you, and you become the expert by trial and error. That means you will kill plants. You will kill plants. After a while, you won’t kill as many, because you’ll develop a better understanding of your extremely local growing conditions. By patient observation you’ll know, for example, that a certain corner is windy, the snow always melts first by the walkway, and the area by the gutter downspout is always a little bit damper.

On the other hand, I suppose you might kill more, because you may become more willing to take chances. I find my willingness to experiment is constrained by the limits of my pocketbook. I will try a perennial rated a zone or even two zones warmer if I think I can provide the other conditions it needs, perhaps shade and moist, acid soil. But I am more conservative when it comes to an expensive tree that requires a lot of digging to plant–and to dig out again when it dies. Gardeners with a bigger acquisitions budget will be braver. Wayne Winterrowd and Joe Eck, in A Year at North Hill: Four Seasons in a Vermont Garden, describe many rhododendrons in their garden that aren’t considered hardy in their zone. But there they are, grown to maturity. Winterrowd and Eck were not assured of success when they planted them.

Graham Rice has a tough job, writing about plants for an area in which he’s never gardened. I imagine after consulting reference works, he’ll talk to friends and colleagues more familiar with gardening in that rigorous climate, and maybe seek out a gardening blog or two. Northscaping, which I’ve mentioned before, is another good source of hands-on cold climate gardening information.

About the Author

Kathy Purdy is a colchicum evangelist, converting unsuspecting gardeners into colchicophiles. She would be delighted to speak to your group about colchicums or other gardening topics. Kathy’s been writing since 4th grade, gardening since high school, and blogging since 2002.

In its own way, frost may be one of the most beautiful things to happen in your garden all year . . . Don’t miss it. Like all true beauty, it is fleeting. It will grace your garden for but a short while this morning. . . . For this moment, embrace frost as the beautiful gift that it is.

~Philip Harnden in A Gardener’s Guide to Frost: Outwit the Weather and Extend the Spring and Fall Seasons

19 Comments… add one

My Flower Delivery .ie July 18, 2010, 4:23 am

Great article,
I can’t agree more with you in terms of regional gardening.
I am from Ireland and know all about the winter months.
BTW, I love your first image of the flower in the snow

Melanie Watts March 9, 2010, 9:47 am

Soil has a lot more to do with plant survival than you would think. I killed lots of plants in my zone 2 garden, that survived in other zone 2 gardens, because of my clay soil.

Dirty Girl Gardening February 6, 2010, 12:53 am

Great snow pic… We don’t get snow where I garden, so it’s beautiful to see it.

A.R.Wadoo January 28, 2010, 11:02 am

Plant hardiness -is a burning issue in cold climate gardening. Geraniums have to be stored warm locations to tide over the winter months in zone 5.I experimented with geraniums for development of cold hardiness. I planted rooted geraniums in March 2008 in the garden bed under the canopy of a deodar tree. In April 2009 only 50% survived through the winter of 2008.The survivals had lush growth and profuse flowering during 2009 summer. All the plants have survived till to date with no sign of low temperature (Minus 5 Deg C) damage. The leaves have undergone reddish autumn hues.

brenna January 24, 2010, 8:08 pm

We are in upstate NY. It is good to learn the information in this post. Thanks.

Kevin January 24, 2010, 8:07 pm

Good article. thank you, I have learned something new.

Paul H. January 23, 2010, 5:10 pm

I am very interested in pushing the limit with some plants as far as hardiness is concerned. Supposedly we’re getting warmer in CNY..the Arbor Day Foundation made a new hardiness map placing (most) of us here in zone 6. I know we’ve been having zone 6 winters recently. I’m currently overwintering outside a “hardy” Japanese fiber banana, some camellias, and a gladiola rated to zone 6. We’ll see how it goes. We have had freak incidents of canna lilies and dahlias surviving the winter outside, possibly due to their location in protected areas (we’re in Syracuse).

Amanda Legare January 23, 2010, 8:35 am

I in north central Vermont and am zone 4, leaning towards zone 3. Thirty below zero would be unpleasant, but not a huge surprise. Scabiosa ‘Butterfly Blue’ doesn’t stand a chance here, although I often see it listed as zone 3. Conversely, anemone pulsatilla, which is usually listed as zone 5, does fine here.

I am constantly experimenting as well and have yet to find a true yellow-leaved heuchera that will overwinter. The same goes for yellow/orange echinacea.

I agree about seeing what works for your neighbors. Best yet, if you have a local nursery that sells field-dug plants, then you know what you are getting will do well. It’s a lot of work, but I am one of those places that sells only “proven” plants. (No, I don’t do any mail order, so this is not an advertisement!) There are a number of similar nurseries in northern Vermont and it’s worth chatting with your local nursery owner.

Cyndy January 22, 2010, 2:31 pm

I grew some stipa tenuissima 3 years ago for a little annual accent and it’s still here looking cute in the winter in zone 5b Connecticut. I wonder if it’s starting from seed that helps – it’s not in a particularly sheltered spot. On the other hand, Artemisia ‘powis castle’ dies here if left outside, so now I dig it up and leave it in the unheated porch. I think it hates getting waterlogged more than the cold temperatures. It’s so true – you will kill plants :)

Belva Lotzer January 22, 2010, 2:00 pm

I live in a solid Zone 3 (temperatures dip down to -40 in the winter and up to 105 in the summer) at an altitude of 5000 ft. I rarely get 65 consecutive frost free days. So although I am not Zone 2 I can understand the frustration of cold weather gardening. The problem is 15 miles one way it is a Zone 5 and 40 miles the other way is a Zone 2, so the whole Zoning issue does make it a little difficult. But I will experiment with plants ranging from Zone 5 down. There are spots in my garden that are well protected and a Zone 5 will survive with protection but not all. That’s what makes gardening so interesting. Finding the right spot for the right plant. For sure contact your local nursery, extension office or neighbors. Check out the local Gardening club, they are often thrilled to help a newbie! But know for sure that you can have a beautiful garden even in Zone 2. I have 3.5 acres in gardens right now and opening up another 3 acres very soon.

allanbecker-gardenguru January 22, 2010, 11:59 am

h I garden in Zone 5 , in Montreal, and the labels on some Careopteris claim that it is hardy to Zone 5, yet none of the nurseries here will stock it, even though their inventories are encyclopedic . That is my guide to whether or not a plant will survive in my Zone.

Kathy Purdy January 22, 2010, 2:59 pm

I can’t use what the nurseries stock as a guide because I am in a cold spot in my area. There are many gardens one and even two zones warmer nearby which can grow plants that would be killed by the cold at my place.

Les January 21, 2010, 8:05 pm

The problem many of us have far south of where you are is not cold hardiness. Even though a plant may be rated as hardy in our zone, those numbers say nothing to our humidity combined with our heat. This also does not take into account areas with high night time temperatures which keep many plants recovering from day time highs. Although labled as hardy in our zone, many a plant will end up mugging out in our summers.
However, of the two problems, I would rather suffer from too much heat vs. too cold.

Kathy Purdy January 21, 2010, 8:09 pm

Tony Avent addresses the heat problem in the essay I linked to. Thanks for stopping by.

Anna/Flowergardengirl January 22, 2010, 3:01 am

Ditto what Les said–but this is a good article. Only you know what will survive. I am not very adventurous these days. I will try new cultivars but only if they are rated for my zone. I do believe in amending soil properly or nothing will survive no matter the zone.

Botany Buddy January 21, 2010, 4:20 pm

Caryopteris will often freeze back to the ground zones 5 and lower but can also resprout from the root in May or June. Scrape the bark at the very base and see if there is any green at all and cut it back to the point the green stops. If it is brown all the way to the ground leave a little stub so you know where it is and just plant an annual around it. You may see several new shoots come up around mid summer. this used to happen to me all the time in Kansas City. They almost always came back once the temps reached the 80’s. They will often act like a late season perennial.

Mr. McGregor's Daughter January 21, 2010, 3:14 pm

I am not encouraged by your dead Caryopteris. I bought one last year and mulched it well before the snow and cold hit, but I worry whether it will join the long list of things that once grew in my garden. On the other hand, Ivory Prince Hellebores survived last winter in my garden (when it got below -20F), and I’ve seen them rated as hardy only to Zone 6.

Kathy Purdy January 21, 2010, 4:00 pm

It is hard to know why it died. We didn’t have an especially cold winter, but we did have an unexpected hard freeze late in May. Quite possibly that’s what did it for me. I would consider planting it again.

Judy Lowe/Diggin' IT January 21, 2010, 2:03 pm

This issue is one reason I recommend regional gardening books so strongly. Nothing beats personal experience with the plants the author is writing about. Thanks so much for bringing it up!

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