"I truly believe snow is Satan's handiwork."

Spoken like a true southerner LOL!

Ken, that qualifies as a bonafide snow job. Snow in Tennessee may be the work of the devil, but in Wisconsin it's divine.

I think the observation about snow and air temperature tends to confuse two quite different issues. Snow cover can indeed cause lower air temperatures through radiational cooling. Snow, however, works like any other insulation. The air trapped within it is the primary benefit to plants because it slows or even stops the exit of warmth from the soil into the atmosphere. Consistent sub-zero or otherwise unusually cold temperatures over a lengthy period would defeat snow cover unless it were very deep, but a night or two of radiational cooling of the air temperature would have little effect on soil temperature and plant roots. The above ground portion is another story entirely. Very good examples of the air temperature vs. ground temperature issue can be found among the many high altitude Himalayan rhododendrons. These are annually exposed to days on end of extreme sub-zero temperatures and high winds. Buried under deep snow, in some cases for eight or nine months, they survive just fine with no winter damage to either roots or foliage. Bring them down into lower altitudes with much more moderate temperatures and little or no snow cover, most are barely Z7 plants in terms of winter hardiness.

All I know is having a thick layer of snow cover, during the few weeks that we are visited with -20's F. , makes the difference between having the ground marginally frozen at the top 6" (temps in the high 20's low 30's F.) and having the cold air transmit down through the ground several feet, with temps much colder.

The insulation comment is correct for above the ground as I think of twros saying that his Hemlocks froze dead 'above' the snow line, during a bad winter.

Some of the areas, on Daves map, should be zoned a little lower as they seem to have a 'micro-climate' going on there. We have low lying areas up north that definitely freeze earlier and much harder in the fall and have later, harder frosts than the surrounding areas in the spring. But I don't think the USDA maps are all that refined and don't include that 100 year winter.

"Some of the areas, on Daves map, should be zoned a little lower as they seem to have a 'micro-climate' going on there."

No not really. Even if they are zoned 7a, -10F is a possibility in that zone. Heavy snow cover south of DC is rare...likewise going below 0F is rare. The PRISM model that the recent USDA maps were developed with takes all of this into account. (in addition to, obviously, NOAA station data)

It would be a microclimate if it happened every other winter. But I bet those small towns have not been below 0F since 2003 or even 1996.

"I think the observation about snow and air temperature tends to confuse two quite different issues." Well I'm pretty sure I wasn't confusing them, since everything I said was in agreement with what you wrote. It's worth noting I wasn't really discussing phenomena in anywhere other than where most of us garden, which is, well, the great CONUS at normal altitudes. At 14,000 ft in the Himalayas, there are other things going on, probably. Most of us are in areas where the (deep) ground temperature is at some stable figure like 55F, so, indeed if you cover that with a heavy layer of insulation, it stays closer to 55F than it otherwise would. At, again, the cost of NOT having that ground heat available to keep nights warmer.

'It would be a microclimate if it happened every other winter. But I bet those small towns have not been below 0F since 2003 or even 1996.'

However, there are areas, within an area, which are more prone to exaggerated swings in temperatures/precip. than the zones depict. Maybe not a microclimate, but still a fact. I'm sure the USDA has calculated all these things into their maps, it's just that when these wild swings do happen, maybe not only 100 years, could be 20 or 40, damage is done to plants classified as hardy to that particular zone.

This could go back to how much the suppliers 'stretch' the classification of the plant, don't know.

TN is an interesting place. We can grow cannas, glads, callas etc. that in a more northerly zone six would have to be lifted and stored for the winter. The same zone hardy woody plants (7-8) are another thing however. Every so often temps here go WAY below zonal averages, making long term survival problematic. I've lived here 32 years, the 80's and early 90's were an absolute nightmare as far as winter lows. Then came the early 2,000's, with virtually nothing below zero and everyone saying that the climate has changed and we can grow palms outdoors. Now in the teens, things seem to be going back to the bad old cold days. The problem is that the lifespan of Homo sapiens is WAY too short to experience the variability of WEATHER (not climate) over a span of human years, rather than geologic years, which define climate, at any given location.

Good example was the big snow in Feb 2011. Stopped snowing afternoon, clearing w/no winds & overnite lows were predicted 5 to 10F. Next morning it was -8F w/ice on the insides of windows.

'The problem is that the lifespan of Homo sapiens is WAY too short to experience the variability of WEATHER '

Yup, it's what kind of weather you had your first couple of decades of your life that forms your outlook on it. Not that we shouldn't clean things up a bit. :)

beng, ice inside the windows is a common thing for a spell up here. :)

Actually, the climate change underway today has been clearly linked to human activities. Whether or not we can reverse it is a fair question, but no serious research still questions the origins of this change. And it is utterly unlike the changes the record indicates happened over the eons; This one is real quick. The spike in CO2 is unlike anything that has ever happened on this planet within the timeframe of life occurring on the planet. Conflating natural variation with an extensively studied and extensively reported-on situation with human-caused climate change strikes me as willfully ignorant.

Tom, I don't know if your post above was aimed at someone in particular or just rhetorical, but the last sentence troubles me, particularly the last two words of that sentence.

The debate is in CO2 vs other environmental changes we have made.

IMO there is no debating our suburban and urban heat islands create warmer areas. Look at tv weather reports or where Japanese maples and Southern magnolias grow best here.

CO2 is also a greenhouse gas. The boy scouts can prove it to you in fish tank experiments. No denying it.

Now, we CAN debate how much effect each ppm of CO2 has.

We CAN debate what regulations will make it easier for the Chinese economy to surpass (further?) ours.

So being conservative me, my 98 MarkVIII, my 97 Aurora and my 68 Mustang believe in rational CO2 emissions restrictions but I'm not a nut taking away your cars.

What I am saying...........is that it is a fiction to say that there is controversy over this topic. Among scientists, there is none. Now, among "scientists" with payrolls easily traced back to the fossil fuel industry, there is still "uncertainty" similar to how twenty five years after all of humanity knew that cigarette smoking was bad for you, there remained claims of "uncertainty". This is exactly the same thing and in fact, the deniers are using the tobacco playbook and even some of the same researchers! Imagine that........a "scientist" who was an "expert" on tobacco/health-related issues is now being quoted a s a climate expert! Yes it is frustrating....this has been understood for ten years now.

Tom, I'm sure glad we agree on one thing, we both love Norway spruce!

Yes, but that statement above is pure fiction. Climate has been studied since I was a kid. When I hear someone begin to bloviate about this vast "conspiracy".....across generations of scientists that never knew each other....and somehow the research scientist is the greedy individual in society! Who in their right minds would go into climate research to get wealthy? It's absurd at best. You could literally go into every other line of work and make more money. Nobody.....not one person...goes into scientific research for the money.

I think we'll just agree on the Norway spruce and be done with it. :)

I thought the double edge sword was going to be about voles or something.

I rarely care when temps hit -15, which happens almost every year, when there is snow on the ground.

Its the days when you have no snow cover and you hit 0 for a daytime high that make me nervous with some plants. Just happened a couple weeks ago.

If you lose the roots, you're done. You get dieback, who cares.

Wow, didn't want to start "one of those" but I guess it's kind of inevitable? Even though it ought not to be.

But to get back to the point I was making...no, it probably isn't that 30-40 miles SSW of Richmond is some especially cold micro-climate. (although it would be logically unsound to say I have evidence to be 100% sure of that!) This is why I specifically asked a weather watcher I know, who used to live in that area, about it, and then mentioned the winds closer to the Bay in my first post. The places that got down to -5F or lower were just the places that *happened* to have heavy snow on the ground - already an anomaly for that area - and where the winds *happened* to completely died down, meaning they were unable to mix layers of the atmosphere. At various times in the past, this has happened all the way over to Virginia Beach, which is the reason every square inch of the state of VA has at some time been below 0F, however infrequently. You can see on the USDA zone that there isn't really a blob indicating that area is especially prone to going below 0F.

http://planthardiness.ars.usda.gov/PHZMWeb/Maps.aspx

Understood! The 'low lying' areas I was talking about in my area are in the same USDA zone but... and this doesn't happen every year either... If there is a 'spotty' early freeze in the fall, or a 'spotty' late freeze in the sping, these are the areas that time and again are hit or hit harder than most of the other places around me.

Dang, I wasn't trying to rile up anyone... :(

I was born and raised in CT, and while it is in the north, it's climate is nothing like WI or MN. When I lived there, as much as I hated snow, I welcomed it for it's positive qualities as mentioned above in regards to growing all sorts of stuff, woody and herbaceous. What most growers wished for was a relatively stable winter with reliable snow cover. Except for the extreme zone pushers, that kind of winter got your stuff through in the best of shape.

TN is another animal entirely, as I suspect is VA, at least parts of it. Our winters are a roller coaster, with wild swings in temps and precip. Two days ago it was zero and below, today it is 60 plus and may reach 70 in the next days. The next 10 days out are forecast to be more like early March than mid Jan. We're also in a transitional zone as far as plants go, the southern limit for some northern species, and the northern limit of southern species, and a changeable weather pattern that is anathema for exotics used to a stable climate with few surprises. True northerners struggle here as do true southerners.

I believe snow cover has the same effects in the north as it does here in regards to temps, all things being equal: it causes ambient temps to be colder than they'd be without snow cover. It probably just isn't noticed that much in a climate that is used to a snow cover more or less for the duration of winter. Here a snow cover is really an anomaly, and is definitely noticed, it is usually part of the weather forecasts as regards to temps.

Those of us growing borderline woodies dread snow cover because we know that it will produce lower temps and exaggerate the 'normal' temp swings. Here the ground rarely freezes, and when it does it is only an inch or two and thaws rapidly when temps go back to average. Winter is considered a planting season, indeed the local nurseries that still field growing are digging now in anticipation of spring shipments.

I sometimes forget I'm posting on a board where most are growing zone appropriate things rather than a zone-pushing board.

No no, certainly not riled up, but just anxious to clarify since it was kind of the point of my post! That heavy snow cover is something that can "randomly" induce zone busting temperature, whenever and wherever it occurs.

Bill, you aren't riling anyone up. There is much to be said for having a civil discussion on climate. After all, it is the limiting factor for what species we are able to grow where we are, and is the one thing we can't do anything about.

'I believe snow cover has the same effects in the north as it does here in regards to temps, all things being equal: it causes ambient temps to be colder than they'd be without snow cover.' Correct, and in that way helps prevent unwanted thawing/freezing cycles that are very hard on everything.

I can remember way back, my dad planted some grafted apple/fruit trees on his land he owned near here (he was also a city slicker at the time) It was the end of February and very little snow when the temps went into the 70's for a good week. His fruit trees started growing with new leave starts. Then reality went back to winter and every tree he planted was dead. A few may have come again from the roots.

Approximately fifteen years ago we experienced a very unusual early winter in which we had no snow, but very cold temps. Even when it finally did snow at the end of December, it was not deep and the cold temps continued. The frost went deeper than 8', which is the depth at which most UG water and sewer lines are buried. You can imagine the troubles this caused.

I planted a couple of native Fringe Trees in late October of that year, and it immediately turned cold. I'm not referring to weather charts, but I'm pretty sure evening temps were consistently from -20 to -30, with several days in which it did not reach -0-. It was brutally cold, even for people who had lived their whole lives there. I just assumed the Fringe Trees would be dead come spring, but they were just fine. I couldn't believe it. There are no conclusions to draw from this very limited experience, but maybe snow insulation isn't as much of a factor when it comes to woody plants as we might think...at least for Chionanthus.

I have a friend that was raised in VT on the Canadian border. The water line to their barn would freeze in winter, so one summer they buried it 11 feet deep. It froze one winter.

I once read that if conditions during "The Little Ice Age" returned to Europe, the city of London would have no water. Their pipes are only buried 2 feet deep.

City water lines around here are about 2 feet deep, for mechanical protection rather than freeze protection.

I am in Canada, my water line from the city developed a small leak, probably from the deep freeze the previous winter. The rule is, if the leak is on my property, I shall pay for the repair, if the leak is on public land, city shall pay. The leak was right at the boundary, and luckily, city paid.

Tom, there are plenty of other blogs for the charged "climate-change" discussions. Please spare this blog & stick to trees here.

Fair enough. I always think this is a forum where intelligent brains are communicating. It pains me to see such gaps still flourish, long after matters have been settled. I guess we can argue about the general shape of the planet-flat or round, and whether or not Elvis is down in Argentina with Hitler. But point taken....

"I am in Canada, my water line from the city developed a small leak, probably from the deep freeze the previous winter. The rule is, if the leak is on my property, I shall pay for the repair, if the leak is on public land, city shall pay. The leak was right at the boundary, and luckily, city paid."

My neighbor across the street had the same problem. The leak was at the connection to the street. Don't know who paid for it but the sandy sub soil we have here required a wide hole to keep from caving in. so to get to the valve that was over 8ft deep, the hole ended up to be around 20 ft wide at the top, which took up most of her front yard. :(

There were some freezing of water lines in my town last year but they said it was the older parts of town where the water lines aren't as deep.

Ken, correct me if I'm wrong, but it seems you are portraying TN to be a horticultural sweet spot on the one hand (large hort industry presence), but a nightmare (evil snow!) on the other when growing marginal plants. Am I reading this correctly?

BTW, a brief history of the hort industry in your adopted state would be interesting. Why did it take hold there?

maackia, I'm a whiner. I'm a cynic and a pessimist. The glass is half empty. Hope for the best, expect the worst. My late wife used to tell me to quit complaining about the weather, I couldn't do anything about.

TN is touted as a 4 season state with a mild climate. I think our average temp is 59F. As I've said our temps can be all over the map. The stuff I want to grow either doesn't like to ride on roller coasters, or can't take those times when the low drops 2 zones below the average. A lot of stuff, exotic and native, get caught by spring freezes fairly often and either lose their foliage or it gets disfigured for the entire growing season, think big leaved magnolias.

In spite of what I consider crappy growing conditions, our native flora does well. Our forests are generally healthy and productive. TN is the number 1 or 2 producer of hardwood lumber, usually trading places with NC. Much of the production is used in flooring and veneer. The area where TN, GA, and NC come together is supposed to have the largest diversity of flora in the US. I'm kinda on the edge of that area. I've inventoried 58 native woody species on my land.

As far as the local nursery industry, Warren County, the county that calls itself the 'Nursery Capitol of The World', (it isn't, not even close) borders me on the east. Lots of nurseries, mostly wholesale, some fairly large but most rather small. TN can't come close to the nursery production of OH, IL, TX, FL, CA, and OR., but it is the largest economy in Warren County. The nurseries grow standard, hardy stuff, some finished, but lots of liners. They are the largest producers of dogwood and peach liners in the US.

The industry got started in the early 1800's by a family that grew apples to make apple brandy, then diversified into fruit tree liners. Interesting because today there are very few fruit orchards in this area. It is hard to get a reliable crop because our spring freezes ruin the blossoms so often. I suspect the weather was either generally colder, or much less erratic back then. There are orchards in east TN where the temp averages are lower and less erratic. Anyway, other families began growing and shipping and it became what it is today.

A nice 60 degree day here today, got lots of work done.

Ken, I don't believe you're any of those things, but I always take note of what a wife says. Did she share your passion for plants?

Thank you for that brief history on the Warren County nursery industry. Very interesting.