Tons?
Forgive me for doubting you .
And
you have made my point.
Apricot
Peach
Sweet Cherry
thrive in Eastern Washington
not so much
in Western Washington.
But
do what you want to.
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One thing your analysis doesn’t consider is length of freeze. The longer the freeze the more effect on cold sensitive plants. Zone by lowest temperature doesn’t tell the whole story as you know. The summers in Seattle are cold compared to where I live, Houston. I air condition to 74F which most Seattle summer days don’t get up to! You also have lows in the 50s in the summer. Citrus for example stop growing after seeing a few 50s nights. We had 14F here this winter. Most people lost all unprotected citrus. I banked mine with mulch and lost perhaps 2 out of 20 inground.
Sunset zones for Seattle?
ZONE 5: Marine influence along the Northwest coast, Puget Sound, and South Vancouver Island
Mild ocean air moderates Zone 5, allowing it to produce some of the finest rhododendrons, Japanese maples, and rock garden plants anywhere.Heaths and heathers thrive in sandy soils along the coast and inland, and katsura trees reach their prime, rarely scorching as they may inland. It’s also fine country for native woodland ferns, trilliums, piggyback plants, vine maples, and dogwoods. Summer highs run between 65 and 70°F (18 and 21°C) along the coast, and between 70 and 75°F (21 and 24°C) inland and around Puget Sound. Such mild temperatures favor leaf vegetables, which are slow to bolt, and flowering ornamentals like begonias. Steady breezes and lower temperatures, especially along the coast,make windbreaks and warm microclimates critical for heat-loving plants.
Average January minimum temperatures range from 33 to 41°F (1 to 5°C),with annual lows averaging a few degrees colder, and 10-year extremes ranging from 20 to 6°F (–7 to –14°C). Some locations (Coupeville, Raymond, Long Beach, Tillamook, Newport) get 10-year lows between 6° and 10°F (-14° and –12°C), but much of the region, especially along the Oregon coast, is mild enough to let gardeners get away with growing plants like Washingtonia robusta and hardy forms of Agave americana. Big freezes do considerable damage when they come very early or very late. And while these occasional disasters clear the slate of most borderline plants, they should not serve as a general gauge of plant hardiness here. Though the growing season averages between 200 and 250 days, heat accumulation is low, and warm-season vegetables develop slowly.
https://archive.seattletimes.com/archive/?date=20030122&slug=gardenrobson22
I absolutely agree that the USDA zone system is overly simplistic and fails to capture lots of nuance, and that the sunset zones are probably better for making planting decisions. The only point I was making here was that I had “run the numbers” using the USDA zone methodology, and that using that methodology we would be moving to 9a whenever they next update their zone maps.
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I’m here at zone 8b/9a near Houston. Lowest temps in 30 years, 10F in 1989 and 14F in 2021. Best time to plant citrus was 1990. Dear me, I planted in 1982 and 1987 so lost them in 1989. Replanted in 2000. Knew how to protect them in 2021 so didn’t lose them all. Would have to say USDA zones OK for anything east of Cascades and east of Sierras. Coastal Washington, Oregon and California not applicable.
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For some things that need heat (like citrus or hot peppers), that’s definitely true, but there are many things that actually prefer a more Mediterranean type of climate, and also like @ramv mentioned above, we have such nice dry summers that we don’t have to worry as much about humidity-related problems during the growing season as much of the country.
And some things definitely grow here that are accurately zone 8/9, like a few species of palms, there are a few nice large loquat trees that produce well around the city. The key is knowing which trees need heat and which ones are fine with cool Mediterranean summers as long as the winters stay relatively mild most of the time. We haven’t had a 10° day since the early 80s, and only a few mid-10s days in the last 20 years. So in that sense, Houston and here have a similar number of extreme cold days, even though our average temperatures are much lower year-round.
Which is to say the USDA zone system is not enough, but still can be a decent starting point for deciding what might grow here, as long as you investigate a little deeper.
USDA zones simply go by winter low temps and do not consider heat units etc. For most things this gives an indication of winter survival.
For instance Ireland has been in USDA zone 9 for a long while. However most of us know that Ireland is not a major citrus producer.
Zone is a necessary but not sufficient condition for winter survival. For instance, You need zone 9B or higher for most citrus to thrive. But that isn’t sufficient as is proven by maritime climates.
Having said all this, I’ve lived in Seattle area for 26 years. During this time Seattle has turned much warmer. Summers rarely used to get into the 80s. Now mid to high 80s are quite normal. Summer night times are quite warm (and unpleasant for folks like me)
So zone pushing is possible – maybe not unprotected citrus yet.
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I love that you guys went ahead and showed people you can get into the 100s also who just a few months ago were doubting you were warmer at all
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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.
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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.
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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.
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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?
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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.
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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.
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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.
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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.