zone transitions across borders

A quick thirty miles north of our farm lies the Quebec border. Yet we have hardiness zone classifications here in the States that jump up by one in crossing that border into Canada. Can someone explain to me how to equate growing zones between our countries? Correct me if I'm wrong: Here, in the USDA (wink,wink) I am in Zone 4 ... but a grower with a similar microclimate in Canada would be considered to be Zone 5. I know the Canadians consider more factors than mere winter lows but I'm left wondering why we need this different point of view.

Then we have the McColls in Australia ... but that's a whole other conversation!

Lost Nation Orchard
Zone 4b in New Hampshire



Edited 1 time(s). Last edit at 01/01/2013 05:02PM by Michael Phillips.

By the USDA standards the area just across the border to the north would appear to be either 3b or 4a, depending on your pin point.

I agree, we should be on the same scale. A North American Scale.

Yep, there appears to be no New England equivalent in Australia, no matter what scale you use. I didn't realize that the weather was so nice across nearly all of the Australian Continent.

Came across this zonal map that has a US scale comparison.



Gopher Hill Apples
Zone 8 in California

Is there much difference between Canadian and US zones? We might confuse each other not understanding the distinctions. I'm in zone 3b by the Canadian zone system. I have no idea what that is in US lingo. Any idea?

Morninglory Farm
Zone 3b* in Ontario



Edited 1 time(s). Last edit at 04/12/2013 01:50PM by Michael Phillips.

Hi Robbie,

USDA US Zones (with minimum temps noted for each) are . . .

Zone 1: below -46 C (below -50 F)
Zone 2: -46 to -40 C (-50 to -40 F)
Zone 3: -40 to -34 C (-40 to -30 F)
Zone 4: -34 to -29 C (-30 to -20 F)
Zone 5: -29 to -23 C (-20 to -10 F)
Zone 6: -23 to -18 C (-10 to 0 F)
Zone 7: -18 to -12 C (0 to 10 F)
Zone 8: -12 to -7 C (10 to 20 F)
Zone 9: -7 to -1 C (20 to 30 F)
Zone 10: -1 to 4 C (30 to 40 F)
Zone 11: above 4 C (above 40 F)

How does this correspond with your 3b?

Gopher Hill Apples
Zone 8 in California



Edited 1 time(s). Last edit at 04/12/2013 01:51PM by Michael Phillips.

I'm very interested to see how Robbie "translates" Canadian Zone 3b to the simpler USDA hardienss zones based solely on winter lows. I started this post thinking add one to the Canadian rating makes things roughly equivalent for comparing orchard to orchard. Agriculture Canada scientists created a plant hardiness map using plant survival data and a wider range of climatic variables, including minimum winter temperatures, length of the frost-free period, summer rainfall, maximum temperatures, snow cover, January rainfall and maximum wind speed.

I have set up signatures for Canadian members with a grower profile with an asterisk* to try to indicate this far more comprehensive approach.

Lost Nation Orchard
Zone 4b in New Hampshire

well, by that USDA table, we're definitely zone 3.... IF we include the temperatures that the orchard has survived through in its lifetime. Perhaps with climate change being active, we've not taken the -40 degree dip for several years.. Tho' it wasn't too long ago that I recall a week hovering between -30 and -40 and watching the wood pile shrink considerably...
In recent years I'd say we're in zone 4.
Thankfully, not in zone 2.
It was the winter of '80-'81 that was a last real test winter, when we lost several of the 50+ year old trees that were here in '69 when we landed here on the farm.
So I mostly plant accordingly with attention to zones... buy many trees from Manitoba... and occasionally play the horticultural lottery, when a variety sounds too good not to include in our plantings.
Also, by the Canadian zone chart, we're listed in zone 3b, tho' my neighbour a mile east has a northern slope and a few weeks longer season. Micro-climates reign.

Morninglory Farm
Zone 3b* in Ontario

I've always considered my CDN zone 4a rating to be fairly equivalent to the USDA zone 4. And in effect -29 to -34C is pretty much the coldest we endure. But the thing is that is only statistics...

I have recorded the min temperature since 1995 at my orchard, so that is 18 years. The coldest seen is -32, then another year -31, and 3 years I saw -30, so that is 5 years out of 18 that I have hit -30 or colder. All other years, the minimum recorded has been between -23 and -29. -23 is the warmest low that I have recorded, and this year it was -26.

However, what would be the probability, on a longer time scale of say 50 years, that the temperature would drop below -34? It is probably not zero. It could happen next year... Is it possible that it could get to -40? - possibly yes... It is just a question of probabilities, but I think I have better chances to record -40 at my orchard during my lifetime than to win a million at the lottery!

So, what bugs me with the USDA zones, is that there can't be such a thing as an absolute minimum. There is always a possibility to get a really cold winter - maybe it will be next year, maybe in 50 years, but sometime, even if you are in zone 5, there is a non-zero probability that the temperature will drop below -29C... What do you do then with the classification?

Jolicoeur Orchard
Zone 4 in Quebec

Please note that the temperatures listed by Paul are NOT "minimum temperatures", but rather "average minimum temperatures".

So Claude in Zone 4 could well experience a -40 every fifty years.

I've measured -26 here in my balmy Zone 5b, with avg minimum temp of -10 to -15 F.

Interesting, Ed...
If I take again those 18 years of minimum recorded temperatures, the average gives -27C (-17F) ... and this would mean I am actually in the equivalent of USDA zone 5? I can hardly believe it!

And if I take the lowest min I have recorded, -32C is -26F, the same lowest you have measured. Something doesn't work there, because I know I can't grow varieties that are for zone 5.
Claude

Jolicoeur Orchard
Zone 4 in Quebec

Odd. Especially since the USDA Hardiness map uses the years 1976-2005.

USDA Hardiness Map

Good discussion

Not one we are likely to solve ourselves, unfortunately.

There is no right answer and no chart that will work for everyone. There are far too many variables.

The USDA zones are based on a 30 year average. 50 year and 100 year records were not part of the ranges, to the best of my knowledge. Ed is right on, they are in fact averages. With weather anomalies becoming more and more common, maybe some of us will be able will be able to grow a trees in a zone higher than we find ourselves today. I don't think it is a wise investment though. Why spend 8-10 years grooming an orchard block for a new (marginal) variety only to have it clobbered by an especially hard freeze or even excessive heat and drought.

I pay the highest attention to my own micro climate. I take the government supplied zones as a basis and am aware of them, but what happens on my property based on my soils, my exposures, my rainfall & irrigation and my cultural capabilities are 10x more important that a chart made by some government entity, on a computer, based on a modeling formula, by an overly classroom educated technician who has never stepped foot on any orchard ground within 100's of miles or kilometers of my growing grounds . . . if he/she has even stepped on it ever.

Gopher Hill Apples
Zone 8 in California

Thinking about this some more, I did some additional research on the USDA Ag Research website and found this quote of the zoning that sums it up nicely

"Plant hardiness zone designations represent the average annual extreme minimum temperatures at a given location during a particular time period. They do not reflect the coldest it has ever been or ever will be at a specific location, but simply the average lowest winter temperature for the location over a specified time. Low temperature during the winter is a crucial factor in the survival of plants at specific locations."

Gopher Hill Apples
Zone 8 in California

Good discussion. I like Paul's comments on each small bioregion being unique.
"test winters" definitely have told us a lot about what zone we're actually in.
I like the term "horticultural lottery" for those experimental trees and bushes that we have to plant, knowing they may not survive, yet wouldn't it be great if they would.
When I sell baby grafted trees, I only sell ones that I know will survive here.

Morninglory Farm
Zone 3b* in Ontario

Germane to the conversation is also to keep in mind the importance of that minimum temp. I am in agreement that the choice of plants has to include so many climatic factors, including its influence on whether or not fruits ripen well in cold climates and if there are enough chilling hours in southern locals to make for fruiting at all. The worst case scenario in my opinion, however is an outright dead individual which more often than not means minimum temperature for survival. Surviving bloom once in 5 years is frustrating, but a dead 30 year old tree is something else entirely. Yes, too much importance has been put on min temp, but it remains quite relevant.

Walden Heights Nursery & Orchard
Zone 3 in Vermont

Todd, what you say is only partially true, as this minimum temperature might be killing or not depending on other conditions... Imagine the 2 following scenarios:
- A good cold winter, with a good amount of snow - cold sets in by mid-December and it remains cold all the way through the end of January, and then there is a week of glacial temperatures - thermometer goes down to -30 F. And, guess what, trees go through without damage.
- A mild beginning of winter, no real cold in December, then in mid-January, a warm week with rain (we've seen that before), there wasn't much snow and a good part of it melts. And then this is followed by the same week of glacial temperatures as above. Result - many trees killed. Because they didn't harden as much and started to lose dormancy during the week of mild weather and rain.

The second scenario is something that is quite common in Alberta for example, and even if their extreme min is no lower than here in Quebec, they are in a colder zone because of that - I think...

And, to give us an idea, we have here Todd, zone 3 in Vermont, and Robbie, zone 3 in Ontario - if both of you would have measured minimum temperatures, it would be interesting to compare...
Claude

Jolicoeur Orchard
Zone 4 in Quebec

I am in agreement, my point is simply to keep in mind that a min temp for a region has a great importance. The other variables like thaw cycles have huge impact, but I am not sure how these could easily be incorporated into the model. Seedling apple rootstocks for instance vary widely in their cold hardiness depending on thaws. Species and varieties having evolved in consistently cold latitudes often have less cold hardiness in milder climates due to thaw periods, since in their historic range the swings did not exist. Late in the season, cold temps were the only thing preventing resumed growth. When stratifying malus baccata here at the nursery, radicle emergence happens before ranetka, antonovka or prunifolia even though it is touted as the most cold hardy. The same can be said of many varieties with regard to budbreak. I would say the best method for assessment of climatic regions is a forum such as this which comments on which species and varieties are surviving and thriving in each area including microclimate data. This would also help with the even larger problem of conflicting zone hardiness listings of the plants.