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Confusion between Zones & Climate
It amazes me what I read on my twitter stream sometimes. A couple days ago the topic of daffodils came up. I mentioned that the daffodils hadn’t started to grow in Toronto. Another “gardener” tweeted it couldn’t be so. Her sister-in-law who also lives in Zone 5 already had daffodils up.
Daffodils at Toronto Botanical Garden, May 6, 2011
I was flabbergasted. USDA Plant Hardiness Zones do not equal climate. It doesn’t even predict the last frost day in spring. Zones only let the gardener know how cold it will get in winter.
Let us compare the zones between Toronto (the closest large city to me) versus the daffodil growing city, Cincinnati. On closer inspection the USDA zones didn’t turn out to be the same. Toronto is Zone 5b, and Cincinnati 6a. But it’s close enough.
What is really different is last frost day in spring. And that’s what is making a difference in daffodils emerging from the soil. The Farmer’s Almanac lists May 9 as the last frost day in Toronto, whereas Cincinnati gets its last frost on April 13. Almost a month apart!
The difference in climate is subtle… these two cities are only 409 miles (658 kilometres) apart in continental North America. Let us examine three cities with the same USDA Plant Hardiness Zones that are further apart. Seattle, Washington; Norfolk, Virginia; and Big Spring, Texas are all 7B. Interesting, isn’t?
I don’t think anyone would argue that the daffodils are coming up at the same time in these three cities. Seattle has a moderate wet maritime climate, Norfolk, a humid subtropical climate and Big Spring swelters in its semi-arid steppe climate.
I don’t even think folks are looking at frost dates to compare these three puppies. But hey, I am going to give them to you anyway because I’m a smarty pants. Seattle, March 10; Norfolk, March 20; and Big Spring, March 27. These last spring frost dates are closer than the Toronto – Cincinnati comparison!
My conclusion? You can’t use climate and zones interchangeably, but if you are lucky you can occasionally get away with sweeping generalities. It’s complicated.
My plea: think before you tweet. On the other hand, no, don’t. It gives me material for blogs!
References
National Gardening Association’s USDA Plant Hardiness Zone Finder
The Climatic Zones of the Continental United States
The Old Farmer’s Almanac. Frost chart for Canada
The Old Farmer’s Almanac. Frost chart for United States
Written by Cristina da Silva
Tuesday, March 6, 2012 in Plants
Read 2,194 times
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Aren’t our zones about 1 number higher than the USDA zones? I don’t bother with USDA zones at all and always use the Canadian ones, after all we are Can”eh”dian
In Ontario the zone numbers are different by 1 zone (ie 6 instead of USDA zone 5), but it seems in the West it closer to the same (Seattle and Vancouver about 8). Weird, isn’t?
Just another comment that doesn’t need to be published. I’ve been previewing your blog for acceptance at Blotanical. There isn’t a feed url listed and I can’t accept it till one is added. Can you add the feed for me, or let me know what it is.
Another thing I noticed is that the www is not included in your blog url, yet it shows here at your site. Any thoughts?
I have just joined Blotanical. I haven’t done all the set up yet. Will get to it over the weekend. I will look into the blog url stuff. I have just changed my website from Joomla! to WordPress. Another transitional thing. Thanks for the head ups. I really appreciate it!
NIce to see the daffodils in the photo but here the things are only starting to poke out of the ground. It was nice stumbling onto you site. Here on the shores of Lake MIchigan, the seasons are a lot different than down your way. I have posted many many photos of this garden area. Jack
It is nice to see daffodils coming up. However, the daffodils in the photograph are last year’s daffodils (May 6, 2011). Daffodils have not come up yet in southern Ontario. Our climate may be more similar than you think! Both areas are close to the Great Lakes, and the latitude are similar. Spring does seem to be earlier this year. So I may see the daffodils 2 weeks earlier, so mid to late April, rather than early May.