Over the last 21 years that I've lived in Phoenix, I've realized we do some strange things here in the desert, mostly because we don't understand our climate. And we don't understand climate because we have modern conveniences, like air-conditioning and as much water as we want right out of the tap. This mitigates the effect of some of the design "Don'ts" that are so common here.
Like block walls surrounding our yards...
Like MY block wall. The block wall that I spent thousands of dollars on. Sure, it's pretty, but what I didn't realize is that I was that I was basically increasing the heat in my backyard by building it.
--block breezes and airflow
--trap warm air in the yard
--store heat in their thermal mass and release it during the night when temperatures drop, adding to the Urban Heat Island effect
--If the wall is a light color, it can bounce reflected light around in your yard and burn nearby plants.
Am I anti-fence or anti-wall? Nope. But if I had it to do all over again, knowing what I know now, I'd do things differently.
I'd install an open fence - something in wood, or metal - even chain-link. Then I'd plant thorny plants on the outside in the alley (natural burglar protection) and vining plants ON the fence. Inside the fence, I'd plant some screening shrubs and some overstory trees that some of the taller vines could grow up into. This would give me some natural AC as the plants would transpire and the breezes would flow through.
So a lot of people don't think that microclimates make all that much difference. How much hotter could it be near a wall with a lot of thermal mass? Well... it can get hot enough so they can grow peaches in Paris - not an area known for peach growing!
Check out this beautiful blog post at Messy Nessy Chic. She chronicles the history of peach growing within the city of Paris - a booming business back in the 17th century. The peaches produced were coveted by royalty as far away as Russia.
How'd they do it? They manipulated their microclimate.
All those things that make block walls a problem here in the hot desert, make them ideal for heating up a cool climate. Here are a couple of quotes from the blog:
"The peculiar architecture, known as “Murs à pêches”, wall for peaches, served to protect peach trees planted near the walls and adapt them to a much colder environment than the fruit is typically used to."
"The 3 meter high walls were more than half a meter thick and coated in locally sourced limestone plaster, giving them a high thermal inertia and the ability to store heat. Their intentional north-south orientation allowed solar energy to be stored in the walls during the day and transmitted to the trees during the night, preventing them from freezing and accelerating the ripening process. Within these walled orchards, temperatures were typically 8 to 12 °C higher than outside."
Let's revisit that last part "temperatures were typically 8 to 12 °C higher than outside".
That's 14 to 22° F higher! And Paris is in a "gentle" climate zone. They don't get up into the 100's for months on end like we do. So I can only imagine what the temperatures are like on my south and west facing walls when it's 112° F.
The upshot of all this? Microclimates matter. A lot.
Visit the blog for more lovely shots of the Peach orchards of Paris.
Love that you are already infecting minds with permaculture, Wayne!
Dredging up an old discussion - I found it in a Google search for mitigating the heat effects of a west-facing cinderblock wall. Do you think large sheets of styrofoam behind the trellises would shield my new vines from the wall's heat while they're getting established? Or plywood?