It’s Very Cold

– Posted in: Garden Design

Written by Noel Kingsbury

My office in rather more of the white stuff than we’re used to


 As a visitor to the US I am always slightly bemused by the discussions of hardiness zones, overhearing conversations amongst gardeners like “I’m 3a and I can’t grow lady’s mantle, but friend is just a few miles away with 3b and it grows like a weed”. When asked “what zone are you?” I feel a bit like when visiting India and someone asks you “what caste are you?” (yes, this has happened). We, in Europe, simply do not use hardiness zones, although the USDA system has been applied here, and there are European Hardiness Zone maps doing the rounds – but we don’t take much notice.

So, with temperatures here plunging to –13C (9F), which I suppose might be regarded as a rather pleasant day in some places where this is being read, but is exceptionally cold for us, there isn’t much else to talk about. And we’ve had several weeks of this. Most unfair. A lot of gardeners wondering what’ll be alive at the end of it, especially after 20 years of mild winters (usually no lower than –5C (23F).

The Zone-language American gardeners seem to speak makes a lot of sense if you live in a continental climate, but not if you live in a maritime influenced west coast climate like us (in Britain) or the North American north-west coast. We ‘westcoasters’ have our winters moderated by the sea, and live in a zone where cold and warm air masses are in constant, and unpredictable, conflict. The neat predictability of the zonal lines on the map aren’t for us. 

If you google ‘zonaldenial’ you’ll hit on a rich vein of gardeners determined to defy the ruling gods (and the lesser gods of the USDA).I first heard the term from Sean Hogan of Oregon’s wonderful Cistus Nursery. One reason we can indulge in zonaldenial is that we have had a lot more plants to experiment with over the last few years. Particularly when plants or seeds of a particular species are collected at higher altitudes or latitudes than the origin of the plants of the species already in cultivation – what is known as provenance. Milder winters (global warming on top of natural cycles perhaps) encourage complacency . We have had a co-incidence of mild winters, lots of exciting new plants (often southern hemisphere) and a consumer boom in gardening. So many nursery managers have grown up never knowing what a hard winter is like (oh, dear, I’m feeling a bit old now).

And… (I’m feeling distinctly old now) lots of youngish men getting into growing exotic or architectural plants. Which is great. But there is that young man thing about needing to prove your elders wrong and you harder than your mates. I’ve been at nurseries where I’ve overheard comments along the lines of “well I’m in York and my Musa basjoo came through last winter, with no protection, and it went down to minus ten!” which gets a response like “well, I’m in Scotland and mine when down to minus twelve and it only had a bit of bubble wrap!”. You get the idea – one up-manship; my plants are tougher than yours, etc. etc.

Beschornia yuccoides


But…. leaving aside my drearily middle-aged comments, what is plant hardiness anyway? It’s a complex phenomenon, partly chemical and partly physical. Key are chemicals which act as anti-freeze, stopping ice crystals forming in cells. Plants show varying degrees of hardiness, and sorreeeee…. there are no hard and fast rules!

One reason there are few rules is that plants experience very different kinds of cold in their regions of origin. Dry cold is often less damaging than wet. I remember when I had my nursery business and a customer from the east coast of Scotland (just those words make Brits shiver) said he grew Fremontodendron californicum just fine; but that coast has a low rainfall. As does London, which means that, if you add in the ‘urban heat island effect’, meant that the South African and Australian stuff I used to sell (for conservatories and sunrooms) often did surprisingly well planted out in gardens. There are huge mimosas (Acacia dealbata) in London squares (but I don’t know whether they’ll be there next spring).

Pennisetum alo_viridescens
Pennisetum alo. ‘Viridescens’


Pennisetum alopecuroides ‘Viridescens’ is hardy but prefers a good freeze to our our damp and unpredictable winters . What makes zones so unreliable for west coasters is that the winter weather is constantly changing: one week is wet and cold, next is wet and mild, next is cold and dry then mild and dry; plants from continental climates sometimes don’t know what to do. Many Pennisetum (Fountain) grasses fail to survive the supposedly zone 9 winters we have regularly had over the last twenty years, but they flourish so well in zone 5 that landscape architects can fluff up their borders with thousands of the things in the Midwest without a worry.

There are so many surprises when it comes to dealing with plant hardiness. One reason for the way that many species survive much colder conditions in the garden than they do ‘back home’ is that in their natural habitat they occasionally will experience weather much more severe than normal, perhaps only once every few decades. This year the Mexican Red Cross were doling out blankets and fleeces after bitterly cold weather swept into the country. I remember Scott Ogden of Plant Driven Design telling me about how in Texas many species which will ‘normally’ get only an overnight nip of a frost will every now and again have to cope with an air mass which has swept down from the Arctic – damage may occur but the plants survive well enough to remain part of the flora. He went on to explain that this air mass will very occasionally (like this year) get down as far as Veracruz in Mexico, which makes it the furthest place on earth where you can get a frost at sea level. I’ve been to Veracruz, it looks pretty damn tropical to me! It also has eye-popping levels of biodiversity. In the rather cushy conditions of cultivation many species which get occasionally frosted stand a reasonable chance of more frequent freezes. So…. roll on zonaldeniars, be sensible, but basically I’m with you.

Chusquea simplicifolia

Bamboo-nuts would love this Chusquea simplicifolia in Xalapa Botanic Gardens, Veracruz State, Mexico. It looks very tropical but gets the occasional freeze.

After I gave up the nursery I moved onto design work with hardy perennials, which are nearly all from climates far more severe than ours, and living in the Welsh borders I am not tempted to be too experimental on the hardiness front. Maybe one day I’ll live by the sea and have one of those fabulous west coast gardens where you can mix and match from different climate zones. Maybe I’ll be a zonaldeniar in my old age.

Kniphofia unknown cultivar


I saw the kniphofia above (red hot poker) at Croft Castle, derived from South African montane grassland species, which get only summer rainfall but thrive surprisingly well in our soggy winters.

For more information on Noel, check out his website and blog.

Noel Kingsbury

Noel Kingsbury

Noel Kingsbury is a gardener and writer based in the west of England. Author of over 20 books, including four collaborations with Dutch designer Piet Oudolf, he is passionate about wild-style planting and bringing nature into the garden.

Noel Kingsbury

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13 Comments… add one

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Frances January 25, 2011, 8:27 am

Dear Noel,
Please never stop writing.

Scott Weber January 25, 2011, 10:58 am

Ah yes…we here in Portland are very aware of the “zonal denial” phenomenon! Almost every gardener I know goes crazy over the borderline-hardy plants and I just shake my head, knowing they’ll be wringing their hands over a pile of mush that used to be a beautiful plant some day…even if not this winter, probably the one after. I don’t really temp fate by buying plants that are on the borderline for us, then again, I’m not a fan of many tropicals…I guess growing in Zone 3 means that I’m still getting used to all that I can grow here anyway 🙂

David C January 25, 2011, 12:14 pm

Great post, showing the differences in moderate places vs. places with huge variations. 4 or 5 of the world’s 7 main life zones exist near my home office, 9 miles hiking or 5 air miles.

The SW USA and many parts of the world are so rugged and diverse, including elevation and latitude, that applying where plants and climate coincide vs. do not, is crucial to garden success. And ignoring that the cause of many, many failures.

We are not unique – travelling from Texas to the Dakotas (temperature), or Pittsburgh to Denver (moisture) changes what can grow, once irrigation or protection is taken away.

Here in Abq, we have something far worse than zone-denialists – arcticists! They brag about how cold it got in 1971, ignoring the overall climate, and use 1 or 2 plants failing as proof of cold – no, try watering. Or maybe their negative karma, placing limits where there are none, killed them…

I thought Hong Kong was the most equatorial place that has seen frost. Maybe not?

Darla January 25, 2011, 2:50 pm

I was just asking my husband the other day about zones and what makes a zone and how do they determine the cut off. Here’s another question, What constitutes ‘heirloom’ seeds? I could not take all of that cold and snow. I do good to get through our 1 1/2 to 2 months of cold here…

island threads January 25, 2011, 2:55 pm

thank you Noel, I lived on the outer Hebrides and the reason I do not like Zoneing is that it does not take into account the ‘wind’ factor let alone the ‘storm force gale’ factor and the ‘salt laden wind’ factor, all of which I feel do more harm than cold, Frances

Shannon January 25, 2011, 7:03 pm

Excellent post! I’ve pretty much given up on figuring out the “zones”. I try to find out where the plant is from, then figure out how to care for it that way. I’ve done pretty well with that philosophy, much better than I would have done blindly following the USDA zones!

Janet/Plantaliscious January 26, 2011, 5:36 am

Wonderful post, I’ve been struggling with the whole zonal thing ever since I started blogging “properly” and interacting with lots of US gardeners. What you say makes total sense. I used to be so tempted by the borderline hardy plants, but having lost a few, and now gardening on a much lower budget, I am firmly in the “it has to be really hardy” category. Though I did get seduced by some tender perennials which I then failed to get through the winter in my new greenhouse… Good to have such a coherant explaination for why the zonal scheme doesn’t seem to fit UK gardens very well.

Byddi Lee - We didn't come here for the grass... January 26, 2011, 11:52 am

If it will grow, it grows! I have lost potatoes to the frost but the pepper plant tucked in against a wall survived. I’ve got perennial broccoli and a kale forest that’s been growing for 18 months. Everything is an ‘experiment’ in my garden!

Christiane January 26, 2011, 8:14 pm

Dear Noel, passionate about plants I understand you completely, but admit to occasional self-indulgence when it comes to an exceptional plant: Being delighted by it, even if it’s only for a few years until the inevitable frost (or dog days) get it, seems worth the risk. And I silence my inner voices by telling them that for my own clients I am much more responsible!

Deirdre January 27, 2011, 4:29 pm

Zones can get even more complicated. Sunset magazine has zones based on more than just winter lows, but on summer highs, rainfall, wind, fog, etc. as well. They are especially specific for the west coast, and almost neurotically so for California. I swear the zones change block by block in Los Angeles.

My new garden (in Seattle) is in a weird little cold sink. I’m a zone below the surrounding area. This winter it went down to single digits Fahrenheit before we’d even had a hard frost. I think my species rhododendrons are toast. I won’t be doing the zonal denial thing anymore.

Denise January 27, 2011, 6:39 pm

Zone info and generalities can be useful guidelines, but those who leave them behind to explore what their specific (and evolving!) growing conditions can and cannot do have a lifetime of fascinating investigation ahead. For example, here in Los Angeles a mile from the ocean, summer’s zucchinis and pepper plants are still producing in late January!

Les January 29, 2011, 8:13 am

I know this is about climate and zones, but I was gladdened to read that there are young men out there interested in growing something other than the most mono monoculture in the neighborhood – a perfect lawn. I am glad to see they are branching out, which is good for people who sell plants and will be better for the environment one hopes.

HA February 6, 2011, 12:42 pm

Dear Noël, a wonderful post, but it isn’t true that us Europeans don’t care about zones or use them. Us Northern Europeans (I’m Finnish, and this applies to at least Swedes as well) are very much aware of what zone we live in (Finnish zone 1 b/Swedish zone 3-4/US 5b), what we can’t grow and what we can hope to grow. I’m not saying there aren’t plenty of zonaldeniars among us, but that’s mostly us hardcore enthusiasts. I think we have a law (or it is a least strongly recommended) that all garden centers in Finland display the hardiness zones for all woody plants.
P.s. I have several books by you and enjoy them very much!

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