Monday, November 7, 2011

in praise of the urban heat island

tomato, post-frost
In the outlying Twin City suburbs- Blaine, Somerset, Waconia, Jordan- there was a killing frost on September 15 this year.

In our St. Paul yard, it came October 22nd. 
We had 5 more weeks of growing tomatoes and basil and zucchini than did someone living 25 or 30 miles away.  As a gardener, this has to be one of the best reasons for living in the city.  I have a growing season that is more akin to that of southern Iowa or Illinois, than that of Minnesota.

There was an article in the Star Tribune about urban heat islands last week.  We were having a rare afternoon out with the kids at the Birchwood cafe in Seward, having just thrown together a retaining wall (in three hours, thank you) at our rental property.  We were worn out and the kids had been relatively good, so we went to have some cobbler and fizzy fruit drinks.  I came across the above article in a paper left behind by someone else. The print edition had a fascinating graphic- a heat map showing the temp difference on September 15 over the entire metro area.  Our part of St. Paul was among the warmest.  Unfortunately, the online version doesn't seem to have the graphic, so you'll just have to imagine it.

I recall a morning last winter or the winter before waking up early one very cold morning and listening to NPR while I made my coffee.   According to the radio, the temperature in Lakeville (about 25 miles south of St. Paul) was -11F.  In St.  Paul, it was 0.  That's a significant difference in quality of life.  Especially since I was catching the bus to work.  And the fact that there even was a bus to catch to work.  Doubt there's one in Lakeville.

So as much as I am supposed to not like the urban heat island as an environmentalist of sorts and regular voter for candidates of the donkey party, I have to admit that I really do.

Five plus extra weeks of fresh tomatoes is hard to argue with.  We still have a few green ones ripening on the kitchen windowsill and a batch of fresh salsa in the fridge.  I really like extending the fall season.  September 15 is too soon to say goodbye to summer food.

okra pod dried on the plant. next year's seed source.

So even though I do have a rain garden and rain barrel, and garden organically, I will not be putting a green roof on my garage or reflective pavement on my driveway.  I like my urban heat too much.  I can understand wanting to mitigate it in Phoenix or LA, or even in New York, but Minneapolis and Saint Paul need all the heat we can get.  Yes, this summer was hot (our astilbes never came back from the 103F heat wave) but that's a blip on the radar when compared to the duration and severity of last year's winter.  And this one is predicted to be similar- another La Nina according to the National Oceanic and Atmospheric Administration's long-range forecast for this winter.
nooooooooooooooo!     image from
My boss- who is otherwise a wonderful guy, is really into cross-country skiing and looks forward to the snow and ice.    He gets excited about each oncoming snowstorm, while I count how many more days it'll be until we have unfrozen soil in the yard.

I suppose his outlook is more healthy, or at least better adapted to life in Minnesota.  And I do enjoy winter for a while.  Maybe the first half of it.  It's the second half, the part after Xmas and New Year that drags.  That causes people to go a bit nuts and drink tequila and go to tanning booths.

Not that I've ever been a tanning booth customer, but I do like getting a little bit of a tan in the back yard.  And that's hard to come by in February.
november's dried-out rain garden


  1. I am not an of cold but if i have to chose cold and hot, i definetly chose cold. I like to have 4 session and spring is my favorite one.

  2. I'm rather fond of the mini heat-island effect in my little ol' yard too. Still have one snapdragon plant in bloom as of this weekend - and just picked my last kohlrabi.

    Was quite sad to be using the last of my counter-ripened tomatoes in my batch of minestrone, though.

  3. I was sad to make the last batch of salsa too. But think about it- it's the middle of November. That's a pretty good run for the tomato plants.

  4. Interestingly enough, I have similar results, even though I am nowhere near an urban heat island. (Walmart is 25 to 45 minutes away in three different directions.) I live halfway up a north facing slope. Exposed peaks and low valleys both had frosts in mid-September, mine wasn't until late October (and I still have geraniums blooming on my porch!)

    Another benefit of being on a north-facing slope is that fruit trees bloom a week or two later -- frequently missing the last frost.

  5. John- that's interesting. I hear that's one reason apple and other fruit orchards are located on slopes or the sides of valleys. The cold air either settles into the low spots in the valleys, being heavier than the warm air, or stays high, being that the atmosphere gets cooler the higher you go.

    Are you in the Rockies, or another similar range? I've always found mountain microclimates fascinating.