Yeah I’m not even considering keeping citrus outside my greenhouse in the winter, but I’m keeping the hope alive on cold-hardy avocados. Despite knowing it’s still a bit of a long shot. But where’s the fun in life if you don’t take a few risks a push a little?
I wouldn’t say I loved that, but I get what you mean. Hopefully that kind of extreme heat is still going to be rare, even if more likely than it used to be.
May June and July are below average in Kentucky…temperatures that is.
So, some get hot, some get cool, some get rain and some get drought.
I am enjoying the below average.
Yeah, and yet when you average them all out over time, the warmth is massively dominant globally, especially for places closer to the poles like Seattle, Canada, Siberia, etc., while the cooler than normal areas are typically localized and relatively short-lived. But I gather any discussion of this area of scientific consensus is considered overly politicized on this forum, so I’ll leave it at that.
I want to say for the record that I was not attempting to elicit a debate about climate change in this thread and was just making an observation about calculating updates to USDA zones, particularly in Seattle.
Scientists say what they say, and we can either accept they are doing their best to understand truth, or we can assume they are all part of some conspiracy to… do something?.. but debating the details definitely leads to too much acrimony on this forum. So let’s not?
well…I don’t agree that it serves any useful purpose to truncate the decades of data and just use the last 20 or 25 years (as if it’s a ‘new normal’) and be constantly adjusting the zone lines.
I’ve seen zone 7 reach Lake Cumberland in south central Kentucky and I’ve seen zone 5 moved all the way south to Lookout Mountain in Georgia in my 6+ decades of observation. A new map using only the last 5 years probably would move us into zone 7 easily…maybe 8. But, that doesn’t take into account it might reach -20 or -30 in the next 5 years for it has done so numerous times.
If I decide to plant zone 8 trees in my area…I m gambling that warmer conditions are here to stay. And I don’t like gambling unless I have good odds.
Zone envy
The USDA zone system, as currently formulated, uses 30 years of data. They may decide to change that with the next update, of course, and obviously extreme weather events can happen that go beyond that range. Anything that is based on averages obviously won’t capture the most extreme events possible.
The USDA growing zone map takes the coldest temperature each year over a 30 year period and averages those 30 measurements, and assigns your growing zone based on where that average falls. It is almost a guarantee that somewhere that is zone 8 will occasionally get cold temperatures below the zone 8 range.
30 data points is hugely different than 5 in extrapolating a trend.
I’d prefer they report an 80 or 90% confidence of not going below a given temperature for the next X number of years, rather than reporting average. But the 30 year average lowest temperature is much more straightforward.
I accept your reasons.
But, I do know some that report stories on such use a shorter period than the 30 year one the g********* uses.
I still prefer the 125 year average if there is that much data for a given location. My low could be 13 or it could be -32…I’ve lived through both.
Damn…125 years…
Who would have thought you were THAT old…
lol
I wish the zone maps took into account climactic changes caused by large bodies of water better… My last 5 winters have been quite mild in comparison to those temperatures 12 miles away at my work. There is generally a 5-10 degree difference between my house and work on many of the coldest days.
Scott
You can drown in a lake that is, on average, 6 inches deep.
The extremes are all that matters in most cases
Just as the drawdowns in a retirement portfolio are more important than the averages. Gotta survive…
Yeah, though in this case it’s worth pointing out that what the USDA are averaging ARE the extremes each year. So it’s more like a lake that over the last 30 years averages 6" in its deepest point at the highest flood stage each year.
Could you drown in it during an unusually flooded year? Sure, but probably not in any given year.
That is why I think Seattle should stay in zone 8. In 10 of the past 30 years it has been below the zone 9 minimum temperature in Seattle, according to the above chart. That is more than occasionally. Here (zone 9a Texas) I would think we get below minimum temperature less than 10 percent of the winters.
Citrus are usually shown to be a zone 9 and 10 plant. And a 5 to 10% chance each year of going below zone 9 would be acceptable. But greater than 30% means you stand a good chance of losing the citrus trees each year. It would be misleading to the gardening public to think they have a good chance of growing citrus when it gets too low that often. Here people would practically stop planting citrus if we had 6 straight years of below 20 degree temperatures.
@garybeaumont those are good points as to why USDA zones aren’t reliable as a sole measure of hardiness for West Coast locales, but the USDA map is based on just that one simple mathematical calculation, and as far as I know they do not tweak those zones based on any other planting-related considerations or % chance of a colder temperature.
If you look at the current (as of 2012) map, there are already a number of 9a pockets in Western WA, and I don’t think anyone there is trying to grow any citrus other than maybe yuzu or something.
Several figs do well in the Puget Sound lowlands. They’re actually easier to grow than most Stone fruits.
Just find the warmest place in the yard.
Bald-faced German Hornets can be a pest.
I live in the Gulf Islands right by your San Jaun Islands. According to the maps I’m in zone 9b. We’ve also experienced record breaking heat so far this spring/summer with no rain for a very long time. I was driving to a local nursery today and saw 4 Turkey vultures at the roadside. I’ve only seen one before in almost 60 years on the island. Guess I should have bought the banana tree I saw at the nursery today. Even the banana tree looked sun scorched.
Decided to make a chart, this one is through the end of 2022, showing what the USDA zone calculation would be from 1977 to present (data starts in 1948, but the 30-year average can’t start until 30 years later):
Can see that the 30-year average has been going up now for the last 40+ years, but didn’t cross from zone 8b to zone 9a until around 2013.
I know that’s a little tongue in cheek, but 
