With global warming (or whatever is going on), the National Arbor Day Foundation has completed and published a new Plant Hardiness Zone map. It's "good news" for many as a major part of the country has been upped at least one full hardiness zone! Check out your location at http://www.arborday.org/treeinfo/zonelookup.cfm (Note: Add /treeinfo/zonelookup.cfm to the address to get right to the map and locator. VERY interesting).
New Hardiness Zone Map: FYI
Huh, seems I've been upped to z7 from a z5a. That's very strange.
Kwanjin, Have you been experiencing much warmer winters over the past few years? Supposedly, accurate temperature records have been monitored since 1990, and that's how they came up with the zone changes. You're certainly lucky if you get to be zone 7, for sure!
Our 5a is based on a coldest low of -15 to -20. We just had -19 the other day and usually have around -17. I don't think the USDA zone is based on any other factors.
No, our winters are cold. 7º this morning. It would be nice to be in z7 but I know not likely to be true. Summers are getting hotter, though. In the hundreds for several days in a row and upper ninties for weeks.
Zone 7 can get all the way down to 0 degrees F, so if you never get colder than 7 degrees then you still could be in zone 7. But Arbor Day put out this new map back in 2006 and the USDA hasn't followed suit yet, and most regard the USDA map as the "official" zone map. I'm waiting to see if the USDA changes their map or not.
Darn, I'm STILL in zone 4. :(
Joan, if it makes you feel any better, I haven't moved zones either...still zone 9! LOL
Wanna trade?
No thanks...I moved here from zone 6, and even that was too cold for me! I'm not sure you'd like the large size of my mortgage or the tiny size of my yard anyway, you pay a price for warm winters! :-)
I'm sure you do. That's one thing that I do tend to take for granted here. I have a yard that's over 5 acres and it didn't cost an arm and a leg. I just wish I had a growing season that was longer than 3 months so I could enjoy it more. :)
This may be a dumb question, but what difference is it if you only go as low as 7 degrees, or as low as 17 below zero. Both of those are considerably below freezing, and I would think that once you go below freezing, that's all that matters to plants. Does the ground become more frozen as the temperature drops below zero? Or are the coldness zones really a reflection of the length of the cold season, since I would expect that the colder you go, the longer the winter season is.
Sharon
I went from zone 7b to zone 8
shebs--sorry I can't give you the good scientific explanation for why, but there are definitely varying degrees of hardiness that plants exhibit as temps get farther and farther below freezing (that's why there are things you can grow in zone 5 that someone in a colder zone wouldn't be able to). Even here in zone 9 we get below freezing occasionally, and there are plenty of plants that survive fine here but wouldn't stand a chance in zone 7, 6, 5, etc. There are basically two factors at work--one is how cold it got, and the other is how long it stayed that cold. I have some plants that could probably handle a few nights in the mid 20's F but if it stays that cold for a week or so, that would probably kill them. Or if they're exposed to one night of 5 degrees F, that would kill them right away.
ecrane, I can always count on you for good information. Thanks.
Everyone sure has added to a great discussion of zones! I think what some have pointed out makes sense, that it's not the occasional low temperatures, but long streaks of cold temps that do "permanent" damage. For instance, I've got some azaleas that are bud-hardy to 0º (plants hardy to 10 below zero). For the past three years, we've had a few winter nights below zero, but they've still bloomed well the next spring. In cold winters they lose more foliage, but they rebound the next year fine.
Down the road, there's a beautiful blue atlas cedar that has been growing for almost ten years and has reached over 12 feet. It's made it here in what is supposed to be Zone 5b through occasional winter temps well below zero and shouldn't be hardy here at all, but is! And it's growing right out in the open, not in a microclimate. This area in central Indiana is seeing other plants surviving now that have never made it for more than a year or two, if that: crepe myrtles, nandina, vinca major for instance. Also, some half-hardy perennials that normally would freeze out are not, such as Verbena bonariensis (zone 7) and snapdragons which die to the ground, but come back from the roots, not by reseeding. Only fifteen years ago, one never saw these plants make it through the winter! I guess the next few years will tell one way or another. I really look forward to a new USDA map, if they plan to update it. Meanwhile, many of us will keep trying to stretch the envelope of what we can plant. (Oh yeah, kudzu vines have made an appearance in central Indiana, too! Now that's really an unwelcome southern pest we never thought we'd have to deal with!)
I'm surprised the National Arbor Day Foundation did this. I agree with the Foundation too. Recent years have been warmer. I'll push a zone on flowers and vegetables.
But trees? Trees are a big investment in money, time and space. Be a shame to take care of a tree for a decade or two and have it wiped out.
In the late 19th century and until World War One, Connecticut was the second largest producer, after Georgia, of peaches in the country. The winter of 1917-1918 --with a 4 foot deep frost--ended that. Had I put in a few peach trees a decade or so ago, they would probably being doing fine. The winters have been mild. But why risk it? Why not plant apples or something else which isn't borderline will be here for the next generation and the one after that?
Hardiness has to do with the cell structure of a particular plant. That is all I remember from horticulture school. It has been a few years...