USDA Hardiness Zone system -- isn't there something better?

fabaceae_nativeNovember 19, 2008

OK, I've seen a lot of interesting discussions on this forum about plant hardiness, and the zone system, so decided to start a thread that will hopefully be interesting to people...

So here's the deal. After finally finding some good historical climate data for where I live going back to the 1800's, I am happy to say that it's a zone 6b.

The funny thing is that most zone maps (Arbor Day's newest one is an exception) and most books, local nurseries, online nurseries with zipcode zone finders, etc. all show it as zone 5. But 140 year old data does not lie, and it shows just an average of 2 days per year with temps below a zone 7 (0 degrees F). Could it be that the definition of the zone system as being based on THE AVERAGE ANNUAL MINIMUM TEMPERATURE is not followed, and instead 10-year lows, or worse, record lows, are taken to define the zones? This seems to be the case where I live, as anything below -10 (bottom of zone 6) is a record of some kind.

Anyone else find this after looking more closely on their own into past temperature data?

Assuming this is just a regional fluke, can we trust zone designations for plants then? And the bigger quesion... is average annual minimum temp the very best way to decide what will survive the winter in a given area(assuming proper care)? On these forums nearly every gardener will ask for more info beyond just a zone number, such as what part of the country? Dry or wet? Sun or shade? etc...

Sounds crazy, but I kinda wish each region had it's own version of what Sunset is for the West Coast... and then an appropriate way to compare across regions. Does anyone else know of other ways to think about cold hardiness ratings? Maybe overall average January temps, for example?

I would love to hear your beef about the zone system, and anything else related...

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petzold6596(8b southern NM)

USDA hardiness zones are the average low temp for a larger geographic area. These values are the result of the temps recorded at the 'official' gathering site, most often a FAA airport. Within that area there are numerous micro climates as well within your own home site. Here in Cruces I live on the East Mesa and the weather here is defiantly different than in the valley as well as at the airport on the West Mesa. You are a better source for determining your growing zone than the USDA. I grow some zone 9 plants here that I'm would not grow in the valley.

    Bookmark   November 19, 2008 at 9:03PM
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fabaceae_native

Thanks petzold,

I guess your point that "you are a better source for determining your growing zone than the USDA" is really the bottom line here.

Strange though that in this case, both the USDA and I are looking at the same data from the same "official" gathering site, so it's not a case of differing microclimates.

I am tired of being cautioned at local nurseries not to try a zone 6 plant, when the thing that made me look more closely into the temperature data in the first place was all the plants thriving here with zone 6 and 7 hardiness ratings.

As you might guess, I'm a big proponent of experimentation in growing, and I think that too often people are stifled by conventional wisdom, or should I say conventional ignorance. Much much is possible in any given place if there is an open mind to make it happen... I suppose the first step then is to make your own zone designation and start imagining the possibilities.

    Bookmark   November 20, 2008 at 11:02AM
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lorna-organic

I have distinct microclimates on my property. I have 1-3/4s acres. Plants in some areas are more prone to wind damage because of wind tunnel effects, other plants are protected by nearby vegetation or fencing. Trees provide partial shade in some areas. The soil in some areas is mostly sand, in other areas it is red clay soil. Some areas get more water when it rains for various reasons.

I've been able to grow hibiscus bushes in NM, which winter over in spite of snow. Yet in Berkeley, California I had two hibiscus killed by frost. Berkeley rarely gets frost but one winter it got so cold my water pipes froze.

Climate averages will be disrupted from time to time. There will be exceptional years when the weather is not average. My second year in NM there was a solid month of 100+ degree weather. I lost a number of plants that year, in spite of daily watering. Supposedly this area never gets more than three days a year with temps of 100 or more!

Lorna

    Bookmark   November 24, 2008 at 9:45PM
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wantonamara Z8 CenTex

I live in the Hill Country on the Fracture Zone of the Edwards Plateau where the land drops off here and there and there are a multitude of confusing weather/plant issues . Nothing like what I imagine New Mexico and Arizona have. Sheeesh, your Zone map looks like a psychedelic op art. Mine is a seemingly simple and logical progression but there in lies the hook. I am high up and the cold fronts at this time of the year come in like sharp wedges and often I am 10 degrees warmer than my neighbor down the hill. But if I snooze I might just loose my Kifir lime. I still notice that even the 1/2 zone differnce cuts out a lot of plants that I grew in Austin but 20 miles away they suffer and complain. I am supposedly in their zone but I do not know. It might be the dryness of my soil. I try riot to be in Zonal denial but because our cold snaps barely last three days . It is hard not to stretch the the zonal requirements of a plant. We normally have a dryish winter with a few wet interludes. Mostly warm days exept for some plunging short snaps . I talk to my girlfriend in Seattle washington and she has the same rainfall ammount as I and the same zone but there all description change into differences. Her winters cool down quick, and stay down till late and they stay wet so plants that sail through my dry winter rot in her winter. She gets to do all those things that need a period of cool to fruit and she gets those tropicals that don't mind the damp coolness that never makes it real low. Now , I haven't even started talking about the differences in our summers (B*TCH Also My pet peeve is there is not a centralized place That I know of where to find this info. Do we have a link here with all this info in one place and an analysis of the info region by region. Could be a good thing to put in the experts category or even in the regional forum.

    Bookmark   November 26, 2008 at 11:17AM
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desertlvr

You almost have to devise your own subzone, based upon microclimates. For instance, in the Mesilla foothills west of Las Cruces, where I have a lot of Zone 8B-hardy palms growing, it is listed by USDA as Zone 8a and Sunset Zone 10. We have carefully measured the winter lows on our property in recent years, and we have had an average of only 2 nights below 20 deg. F in the last 3 winters (down to 18), making it a solid Zone 8b, almost Zone 9a.Much of neraby El Paso, TX, is solidly Zone 9a. Not only that, but Sunset Zone 10 has the LC and EP areas in the same zone as Albuquerque and Amarillo, TX, where the nights frequently get much colder. We have large well establisher specimens of W. Filifera and Robusta, as well as P. Canariensis and Dactylifera, which would die in the latter 2 afortementioned places, so the Sunset Zones, while very useful for the Pacific coast, are almost absurd for the Intermountain West. Our property is above the Mesilla Valley, and our temps are often 5-8 degrees warmer on winter nights, which is maybe why we are able to grow date palms, canary island palms, Butias, Sabals, Braheas, etc. without winter frost burn, up on the higher ground.

    Bookmark   November 30, 2008 at 10:58PM
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fabaceae_native

Thanks, everyone for your interesting additions to this thread. Desertlvr, your response includes another perfect example of how the zone system is just too general. It consistently shows valleys as being in warmer zones than surrounding uplands, something all of us here in NM know is not always true.

For example, most zone maps show the espanola valley of Northern NM in Zone 7, and surrounding higher elevations in zone 6, but every time I watch the weather report, the nighttime lows for the former location are colder than for Santa Fe, for example, nearly 2000 feet higher. Obviously this particular valley is a major cold air drainage, and although daytime highs are often a few degrees warmer than the higher terrain, nights are in fact colder, especially so under clear skies (which always produce the coldest temps here).

I guess more than anything this post has reinforced my confidence in establishing my own zone designations for a given area, and for continuing to experiment with plants that are not typically grown in the broader area due to zone generalizations.

A few examples of these that have already survived a few winters:
Ferocactus wiszlizenii (spelling)
Yucca whipplei
Echinocereus engelmannii
Echinocereus stramineus
Agave deserti

Currently trying: (with protection)
Agave americana
Pomegranate
Fig
Asian Persimmon
Windmill Palm

    Bookmark   December 4, 2008 at 11:21AM
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petzold6596(8b southern NM)

Everyone has to remember that cold air is heavier than warm air and will sink. Thus valleys are always colder than the surrounding highlands. I live on the east mesa of Las Cruces where we are constantly 2 to 5 degrees warmer than the valley all year long. In the fall, winter and spring the morning temp drops up to 2 degrees when the sun rises above the Organs. If you live the east slope of the western highlands your temps could be warmer than either the ridge or valley cool/cold or warm/hot, depending on wind direction, because air rolls over the ridge and creates a warmer microclim. Confused? Just do what desertlvr did and be happy.

    Bookmark   December 5, 2008 at 10:53PM
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desertlvr

petzold is exactly right..... the east slope of the West Mesa is the warmest area on our property, with the earliest warming in the AM after sunrise, and the warmest overnight temps from what we both described. Everything I have planted there requires no winter protection. In an area with differing elevations, the microclimate will give you up to a zone difference in what will be reliably hardy for you.

    Bookmark   December 11, 2008 at 7:47PM
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fabaceae_native

Hooray for Arbor Day!

I just checked out the website and used the zip code zone finder. It came back with zone 6/7 for Santa Fe, NM (87505). On top of this, it said, "if this seems inaccurate, you may be in a microclimate", and then gives a link to a definition of microclimate. Fantastic way of presenting this, and a far cry from the other zone finders I've seen that simply come back with "zone 5" for the same zip code!

    Bookmark   December 12, 2008 at 11:08AM
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aikanae(z9b AZ)

The hardiness zone system is useless for me. I've never had a freeze. I'm in an old wash so I get more rain and water run off from the surrounding area. I don't get as hot as people just 5 minutes away. I end up being able to grow a lot more than what anyone says I can fairly easily - so I'm not really complaining either. It's just useless.

    Bookmark   March 3, 2009 at 12:01PM
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Dan Staley

Late to the party, but I use Sunset magazine for climate zones.

Dan

    Bookmark   March 10, 2009 at 3:29PM
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gpd79(Home Z 6B, Summer home Z 7A)

I know this is very very late into the conversation, but I have a question I'd like to ask.

I think the points that you all raise are very good points. I'm particularly interested in fabaceae_native's method. I was trying to get the historical climate data, but I was having trouble finding that information. How did you gain access to that information? I want to look up look at my area's historical lows as well because zone information seems to be conflicting. Some sites say it's 7, some say it's 6b, the people at the local Home Depot, Lowes, and nurseries all say something like... "we're not reeeally zone 7, we're on the cusp." So, I would like to be able to examine my area's lows as well. Is there a good site for doing that?

Thanks!

    Bookmark   July 27, 2009 at 1:10PM
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lazy_gardens

I rely on the Sunset Western Gardens zoning ... they take into account far more than the USDA, such as heat and humidity.

    Bookmark   July 27, 2009 at 5:30PM
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gpd79(Home Z 6B, Summer home Z 7A)

Yeah, I would be interested in looking at Sunset Western, but I live in NJ, so it doesn't apply. :-( They need to make a Sunset Eastern! :-D

    Bookmark   July 27, 2009 at 7:51PM
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petzold6596(8b southern NM)

Intellicast.com has historical weather records for areas with an official NOAA station. Once you reach your weather area, click today's forecast. Scroll down just past the line graph and click 'historical averages'. Play around and there is more.

    Bookmark   July 29, 2009 at 8:45PM
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