The idea of growing zones has limited utility. At best it’s a shorthand. Absolute lows temps are trending strongly upward, as is length of season in most cold places. But volatility is also a huge factor, and that seem to be increasing quite a bit as well. The jet stream seems to adopt a tall sinusoidal pattern for much of the winter, bringing extreme cold to places that don’t typically experience it, leaving mild warm air to its north in most cases.
Hobilus makes a good point about USDA hardiness zones. However, chill hours are the matter of concern with fruit & nut growers in the western U.S. and other locations worldwide. Some areas no longer receive adequate chill hour counts from 10/1 to mid March for certain perennial crops.
The temps seem to have already shifted up at least a half a zone in the last 30 years here about an hour north of Manhattan. I don’t think chill hours are soon to become a matter of importance, and I agree with the post suggesting the man issue right now is mild winters with sudden dips in late winter and/or very early spring. Last year it dropped to 19F on the last week of March, and destroyed my nectarine, plum and pear crops, although the male part of flowers were not damaged- the ovaries were killed.
This year we suddenly dipped to -7 and a similar thing happened to my apricots, although more of the male parts were killed. However, the flowers that survived and were tended by bees bore no fruit so it looks like it’s destroyed ovaries again.
This has happened two of the previous three seasons to some degree and I was completely unaware of it as a possibility- that is the female parts dying while the male parts survive. Now I wonder if it didn’t happen in the past and I failed to identify it. It may be something that has not really been recognized in the literature in general.
So maybe its the result of milder winters, maybe not, but I believe it is. Average lows here used to be between -10 and -15 and as long as it didn’t get lower than the -15 number we’d get peaches unless they were hit by something under about 25F somewhere around bloom. Now anything past the mid negative digits seems to be a kind of test winter.
we had that 2 winters ago. had 3 days of it. -41f, -42f, -44f. that’s solid z3a temps yet i had some z4 hardy stuff survive with damage on the nw side of the plant and had 2 z3 rated trees die completely. i would love it if we went to z5 here. would open up many possibilities like peaches, sweet cherries and paw paw.
I work in the wine industry, and recently attended a talk where the speaker was emphasizing that as an industry we should be more concerned by changes in temperature extremes rather than changes in average temperature. Or in other words, how much your average temperature increases is less important than what’s driving that increase. Ten days of record-breaking high temperatures can increase your annual average just as much as a slightly warmer winter, but the first scenario is going to be far more problematic. On the other hand, your region could be having alternating periods of record high winter temps with record lows, in which case your average temp would be unchanged, but your plants would not be happy at all.
For example, where I am in California, the average annual temperature for the last few years has been higher than the mean. Most of that increase was due to heatwaves (we had 7 consecutive days over 100 last year) and less so to warmer days overall. As a grape grower, we aren’t really concerned about chilling hours, but heatwaves have huge impacts on fruit quality and our ability to work in the vineyards, not to mention the increased risk of wildfires. I would gladly take a summer where every day was one degree warmer than the average high over a cool summer with two weeks of days where the daily highs are 10 degrees over the average.
Here in the midsouth where it rarely gets seriously cold, over several decades of growing things, I have found that the coldest winters result in the least amount of injury, and the mildest winters result in the greatest amount of injury. No matter how much absolute (potential?) cold hardiness a plant has, it better be fully dormant or it will not be hardy.
Many people seem to think that moving up a zone or two will allow them to grow things that they never could before, but I think it is more likely that the opposite will occur. If winters continue to get milder with many prolonged warm spells, but with the occasional polar vortex plunging deep into the south, it will likely get much more difficult to grow the things that used to do well.
Pretty much what I was alluding to; it doesn’t matter if a tree is happier 90% of the time if it up and dies the one year when things go FUBAR.
And let’s not forget the narrow scope of USDA zones. I can’t grow hops here because the plants, while all sorts of hardy, take their flowering cue from days growing shorter. By the time that happens here it is winter already. Then there is the January meltdown, when we can experience a week of warm weather. Every single tree grown here has one thing in common; it can ignore that early signal to break dormancy. Anything that doesn’t do that and get hit with sub zero temperatures the very next day is dead, regardless of how mild the entire winter can be.
Long story short, there are no broad answers as to what climate change will entail. We all need to sort out what it will mean for our particular neck of the woods.
Welcome to the southern plains. All the plains states for that matter. We regularly alternate between beautiful warm weather in winter and vicious cold snaps. Not just spring, fall, or mid-winter, but anytime we can get blasted. Some of our most damaging cold can come in fall. About three yrs ago our coldest night of winter came in October. The next yr we were below 20F for 36 hrs straight in October with trees in full leaf. My pecan tree may never recover from that. A major limbs leafs out two weeks late and is dying back.
The yr after that it didn’t freeze until January 1st. That was the only yr here where pecan leaves yellowed up and fell off as they should. Usually they get froze off, or frozen ON the tree.
I recently crunched some numbers on this exact topic. I’ll post the results later once I’m back at my PC but the gist of it was the following:
Your USDA zone is an average.
Some years you will have minimum temperature a half or whole zone higher or lower than your average. This matters a lot for zone pushers because that hardy citrus you’ve got may be fine in Z7b, but it’ll get murdered after a few years of flourishing because you get a random Z6b winter. Alternatively, if you’re in Z8b and you decide to push your luck overwintering tree tomatoes, you’ll have a decent shot of doing so, even if technically you can’t because of your USDA zone.
The average low has risen at a faster rate than global average temperatures.
At least for the data I ran, which was just eastern North Carolina. But intuitively this makes sense. Global average temperature increases are skewed low by the tropics and by summer. Because of how climate works, the tropics are seeing far less change in temperature as the poles, and summer temperatures are changing less than winter temperatures. In the data I ran, if remember correctly, I was seeing almost +5 F in just 30 years.
I’m dig up the data later and post more detailed information
Oof… I know you get a lot of snow usually at those temps- have you considered doing something like 5 gallon buckets or some other thing to insulate your grafted portions for keeping the varieties alive? I remember you mentioning you piled on the snow to insulate Hardy Chicago.
Obviously you run the risk of rodent damage but with hardware cloth etc that could be mitigated. Just some thoughts.
Regarding the topic on hand,
I expect late frost and early spring high temperatures to become our biggest challenge in Western PA. I lucked into planting Nikita’s Gift persimmon and jujubes as some of my initial trees- they tend to wake up later than everything else. I may begin selecting more varieties that wake up later for this reason.
On the flip side, waking up late leaves less time to ripen fruit! So it’s a double edged sword on all counts.
Welcome to the forum! I’d love to see the data for this. I did some similar crunching in college during quantitative methods and a climate change course but 13/14 years ago when I took those courses is an eternity for our current understanding of the topic.