Talk:Hardiness zone

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Merging other hardiness zone articles[edit]

All 3 articles are stubs and overlap. Let's consolidate the info into a meaningful article. -- P199 13:52, 5 May 2006 (UTC)

Support - Merging 3 stubs into 1 actual article sounds like a good plan :) I'm hoping to add some content and several links, but I don't want to start until after they merge (If they merge). Doc Tropics 03:13, 17 June 2006 (UTC)

Support - I could imagine the article being cleaner after merging. Hey, Doc Tropics, I hope you (or someone else) will edit to note that The Arbor Day Foundation has again updated their map. "2006 Hardiness Zone Map" Due to the implications in the climate change debate, the mid-December 2006 release gained coverage in the Washington Post, the New York Times, among other newspapers. Also, because this is clear, undeniable evidence of climate change, I believe it begs the question, why hasn't our federal government revised the map since 1990? "Harvard's Brief History of Hardiness Zone Maps"User:JohnBonitz 25 December 2006 (UTC)

Hi, just thought I ought to introduce the "Cold Hardiness Zone Map of the British Isles" It's been around for many years now, but you evidently haven't seen it. The map you have for the UK is basic and only shows the 4 zones. It's sort of correct, but the British Isles is far more complex than that, which the "Cold Hardiness Zone Map of the British Isles" has done a lot to rectify. You may contact the administrator of the site for a flat image if you so wish.

Against - Those who are looking up this subject matter rather have relevant information to one section or region. Forcing the article to be "unified" defeats the purpose of the subject and weakens the benefits of wikipedia in general. This also smacks of anti-American bias. —Preceding unsigned comment added by (talk) 23:30, 3 May 2010 (UTC)

US and UK hardiness zones compared[edit]

Despite the warming effect of the North Atlantic Drift on the British Isles, somehow the Shetland Islands and truly subtropical southern Alabama having the same hardiness zone did not seem right to me. Looking at the USDA hardiness zone map for southern Alabama, it shows it as mostly 8a (10-15° F average minimum), with the Mobile Bay area as 8b (15-20° F average minimum.) The US system is defined with Fahrenheit ranges and the UK system with Celsius ranges. Compare this to the Shetlands on the 8-9 boundary of the UK system, or approximately -7° C average minimum (19.4° F.) While the annual minimum temperature in the Shetlands is similar to Mobile Bay, the average winter temperature of the latter is greater due to greater daily ranges and higher daytime winter temperatures. Heff01 04:58, 16 August 2007 (UTC)

US Hardiness Zones[edit]

The USDA updated the US Hardiness Zone map in 2003, it led to significant reclassifications in the the Deep South, including moving Atlanta, Charlotte, Birmingham and Memphis from Zone 7 to Zone 8. I cannot find a 2003 map that is from a source eligible to be uploaded to wikipedia. I have also searched for an Australian, NZ and South Africa hardiness zones map and found a few, but whereas the maps were from the respective Australian, NZ or South African government, I could not update them to Wikipedia in the same manner that the US Government publications are open source and eligible for publication here. Any Ideas? —Preceding unsigned comment added by (talk) 12:07, August 24, 2007 (UTC)

Sunset Climate Zones[edit]

Since there's apparently a discussion going on about merging some articles, I don't want to upset the apple cart. However, I would suggest that any new article contain a somewhat more fleshed-out reference to Sunset Climate Zones, also known as the Western Plant Climate Zones.

In the western US this system is used almost exclusively by gardeners. I'm a pretty avid gardener and have been for 30 years, and I had actually never even heard of the USDA's zones until about 2 years ago.

I would add something myself but as I say I'm not entirely clear on the status of the merge being discussed above. Thanks. Gilajones (talk) 01:35, 8 January 2009 (UTC)

Northern Europe (Scandinavia) hardiness - the system used locally[edit]

As is correctly stated in article, the US hardiness zone system, based on coldest winter temperatures, does not work well in northwestern Europe - Norway, Iceland, Faroe islands, partly also in Sweden, etc. In Norway and Sweden there is a different system based on both summer warmth and length and winter cold. These zones are named H1, H2 and so on to H8, and there is also a mountain zone, where gardening is more ore less pointless (unless using only arctic-alpine plants). H1 is the warmest, H8 and mountain zone the coldest. The latest map uses updated climate data. For instance, Malmø and Gothenburg and Karlskrona are all H1, Stockholm are mostly H2 as is Gotland island; Karlstad and Uppsala H3, Gävle H4, Umeå H5, Østersund H6 and Luleå at the H6-H7 border, Haparanda H7, Vilhelmina H8 and Kiruna in the mountain zone. For Norway, Mandal, Stavanger and Bergen are H1, Kristiansand, Tønsberg and Ålesund are H2, Oslo (lowland near the fjord), Norheimsund in Hardangerfjord, Molde and parts of Hitra island are H3, Trondheim, Hamar and sheltered locations in Lofoten archipelago are H4, Lillehammer, Mosjøen and Fauske are H5, Harstad H5-H6 border, Lom, Mo i Rana and southern part of Senja island H6, Oppdal and Tromsø H7, Alta and Geilo H8, Røros and Karasjok in the mountain zone. As seen, the result is quite different from the US system. Oslo is here in a much milder zone than Tromsø (due to warmer, longer summer), and this is of course correct. Oak trees grow well in Oslo, but would strive to survive in Tromsø and grow very, very slow. As with all such system, the local microclimate can vary a lot depending on shelter or windy location, sun exposure or shadow, etc - even the same garden can have different microclimates. Here are some examples for well known plants: The hardiness of European beech - Fagus sylvatica - is H4 (inland) and H5 (coast). Quercus robur is H5 (inland) and H6 (coast). Norway spruce is H8 and Blueberry grows well into the mountain zone. Taxus baccata is H4 (inland) and H5 (coast). Sequoiadendron giganteum is H3. Prunus persica is H2-H3. Apple trees (able to ripen fruit) varies from H3 to H5 (a few even nearly H6), and are commonly used in private gardens at least up to H4/H5 zone. Orcaborealis (talk) 20:12, 22 January 2009 (UTC)

I have to say I have never heard about these H1–H8 zones being used in Sweden. Does that system have a name? Unless things have changed very recently, the only one in use among amateurs in Sweden is the one with the zones named I–VIII: [1]. I know it as created by Sveriges Pomologiska Förening, but there seem to have been name changes and mergers semi-recently, so it's now © Riksförbundet Svensk Trädgård (and bloody expensive to reproduce). JöG (talk) 22:43, 25 September 2009 (UTC)

But my real point (and possibly Orcaborealis's too) is that it's not really helpful to have the article speak about zones in Scandinavia and implicitly use the US system. Might be mildly interesting to US citizens, but to the rest of us, statements like "Pajala is in zone 3" at best carries no information. JöG (talk) 22:51, 25 September 2009 (UTC)

You are right, the US system used in Scandinavia carries very little information, as summer warmth and length is very important in Scandinavia. And yes, I was referring to the same zones you linked to. In Norway, we use H and then number, but it seems only the number is used in Sweden, which you probably know quite well. My reference is the map produced by Det Norske Hageselskapet in Hageselskapets sortsliste (Media Øst, 2005, ISBN 82-994640-2-1).Orcaborealis (talk) 12:10, 27 September 2009 (UTC)
I've never heard of this system being used in the UK either. It may be used by professional horticulturalists and other specialists but the general public is completely unaware of it. I'm an amateur grower and haven't seen the concept used in books or online forums. --Ef80 (talk) 10:09, 5 May 2010 (UTC)
It is the same system in Sweden and Norway. A map for Norway here.Orcaborealis (talk) 07:07, 6 May 2010 (UTC)

About Northern European heat zones: Why is Oslo listed as 1 and Stockholm listed as 2? Their summer daytime temperatures are very similar. Actually, the warmest month ever recorded in Scandinavia was July 1901 in Oslo, with a 24-hr mean of 22.7°C. Orcaborealis (talk) 14:33, 11 November 2010 (UTC)

How accurate are the tables in this article?[edit]

In the article text, under Australian Hardiness Zones, appears the following:
"...Sydney residents can choose between Zones 3a and 4b."
The numbering of zones is stated to be based on an area's average annual minimum temperature in degrees Celsius.
Wikipedia's own article on Sydney clearly shows Sydney's mean minimum temperature as 13.8 degrees Celsius, far above -40 or -35 degrees. It's not even a simple use of degrees C instead of degrees F, because both scales are the same at -40. Should we need a discussion on the difference between mean and average, I would postulate the difference between the two is unlikely to be around the 54 Celsius degrees mark.
The article also alleges:
"As an example, Quebec City in Canada is located in zone 4 but can rely on an important snow cover every year, making it possible to cultivate plants normally rated for zones 5 or 6, whereas in Montreal, located in zone 5, it is sometimes difficult to cultivate plants adapted to the zone because of the unreliable snow cover."
According to Sydney's lowest minimum temperature since 1859, was 2.1 on June 22, 1932.
How can Quebec City, with an average January low of -17.6C, be in a higher rated zone than Sydney?
Is there some sort of misprint with the table?
If there is not, then the whole idea of Hardiness Zones, as described, seems pointlessly inaccurate.
What am I missing here? Or is the article a furphy?
Bigharps (talk) 05:29, 29 May 2009 (UTC)

Read the article. Quote: Australia numbers its climate zones differently but these can be made roughly equivalent to North American hardiness zones by adding an offset of 6. For example, Australian Zone 3 is roughly equivalent to North America Zone 9. The higher Australian zone numbers have no US equivalents.

So Zone 3 in the Australian system is roughly equivalent to USDA zone 9.Orcaborealis (talk) 17:58, 29 May 2009 (UTC)

Still, Zones 9 and 10 are shown as having average minimum temps of -7C and -1C. Even with the offset of 6 positions, this does still not relate in any way to Sydney's average minimum of +13.8C. I can only assume this rating impractical for Australian conditions, except for the minuscule alpine areas ? Bigharps (talk) 05:07, 30 May 2009 (UTC)

The cold-hardiness of plants depends on the temperatures that the plant has to survive during the winter. During the winter months, the typical daily minimum temperature in Sydney is around 5 or 6 degrees. Actual frost is quite uncommon in Sydney proper. I have no idea what that 13.8 C figure you are quoting is.Eregli bob (talk) 04:59, 19 May 2012 (UTC)
The average minimum of 13.8 C you are quoting for Sydney, is obtained by taking the minimum temperature occuring on all of the 365 days of the year, and averaging them. So if the daily minimum is 20C in summer, and 14C in the spring and autumn, and 5C in the winter, if you average those over the whole year, you get 13.8 C. This is a completely different statistic to the average extreme low temperature which is the basis for the horticultural zones in North America. The typical winter daily minimum in Sydney is 5 or 6 C and the typical annual worst-case temperature is about 1 C.

Adding to 'Some European cities'[edit]

I recently added Cardiff and Belfast to the European city list. I think their inclusion is warranted since they were two of the few European capital cities missing from the list. Someone has since came along and added 2 new Russian cities (which frankly I'd never heard of!!). Aside from not bothering to put them in alphabetical order (which I sorted out!), if everyone decided to add their local European city to the list, things are going to get out of hand! Therefore only capitals and cities notable due to their location or microclimate should be included. CrackDragon (talk) 02:05, 17 July 2009 (UTC)

Cardiff - has Wales become an independent nation? I believe the Russian cities are more relevant, as they illustrate the full range of climate for the continent. Orcaborealis (talk) 07:43, 20 July 2009 (UTC)
Wales, Northern Ireland, Scotland and England are all separate countries within the United Kingdom. That's why they all have their own international football and rugby teams. Even though other countries have semi-autonomous regions, none are as distinct in their own identity as the 4 countries that make up the UK. CrackDragon (talk) 13:18, 20 July 2009 (UTC)
Agreed. Scotland, England, Northern Ireland and Wales are four separate countries, and I don't see why Edinburgh, London, Cardiff and Belfast shouldn't be on that list. Let's also include Braemar and Torquay to get the extremes.

Some thing that annoys me however is that unregistered users pop in and change zones at will, especially in Europe. Like, Amsterdam in 7? Hamburg in 6? If one uses cold records instead of the mean of the coldest days in a 20-30 year period that would be correct, but believe me, -17C in Amsterdam or -23 in Hamburg is far beyond the coldest one might expect in the average winter. Maybe an idea to make this page semi-protected? Clint.hotvedt (talk) 20:29, 28 September 2009 (UTC)

North American Zones[edit]

It is great that the USDA has made its own conception of plant hardiness zones in Canada, but the relevant source for Canadian zones is really, from Natural Resources Canada. This exists only in a link at the bottom of the page, but it should be written about in the North American section of the article. —Preceding unsigned comment added by (talk) 18:50, 10 January 2010 (UTC)

The North American Zone section states twice that it was updated by USDA in 2012. Following the links and crawling through the USDA website would indicate that the update was for the United States only. Provide a link to the complete 2012 updated North American zone data or indicate that the update was the United States only.Sandboo (talk) 13:59, 11 March 2012 (UTC)

External Links[edit]

There is an interactive version (uses google maps api) of the 1990 USDA plant hardiness zone map that may be a better reference for readers than the static version currently listed. There is also an interactive map for the UK and Ireland using USDA classifications. —Preceding unsigned comment added by Peterusso (talkcontribs) 21:16, 28 February 2010 (UTC)

I changed the Boston hardiness zone to 6 (from 7), as per the USDA hardiness map at —Preceding unsigned comment added by (talk) 03:48, 23 March 2010 (UTC)

Australian Hardiness Zones[edit]

I had never heard of the "Australian System" until I read this page. All the documentation I have seen uses the USDA system. I've modified the entry in the following way:

  • Mention both systems.
  • Link to ANBG article about Australian zones.
  • Remove irrelevant reference to the dryness of the continent.
  • Remove copy-and-paste of zone summaries from the ANBG article.

I also recall seeing another system again, based on the dryness or average top temperatures, and used in conjunction with the USDA system. I think Diggers Club uses it, but I can't find any reference to it offhand. Can anybody help? Groogle (talk) 23:14, 10 November 2010 (UTC)

Average annual minimum temperature[edit]

Average annual minimum temperature means what, exactly ? An average of the daily minimum temperature taken over all of the days of the year ? Or the minimum temperature of the coldest day of the year, averaged over a number of years ?

Is this based on standard temperatures taken 1.6 metres above the ground level, or ground level temperatures ?Eregli bob (talk) 04:51, 19 May 2012 (UTC)

Answered my own question, they get the coldest temperature occuring on the coldest day of the year, and then average that number over at least ten years. So the average annual minimum temperature is the expected value of the coldest temperature you are likely to get in a year. Also, about half of the years, you will get something a bit colder.Eregli bob (talk) 05:35, 19 May 2012 (UTC)

US cities[edit]

I've updated USDA hardiness zones for a few cities in the "U.S. Cities hardiness zones" section with results directly from the USDA website (and more of them should probably be checked): (talk) 19:18, 3 December 2012 (UTC)

Northern bias??[edit]

I was dissapointed to find out there's a section on Northern and Central European zones, but nothing on southern european ones. Yet the Central european zones includes well known non-central places as Malaga and Madrid. How about a more generic heading, even if more info on certain areas is yet to appear? Mariannep (talk) 11:44, 20 March 2013 (UTC)