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The Impact of Microclimates...block walls in Phoenix and the last Peach orchards in Paris

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 walls:

--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.

Like what?

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.

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Thanks to both of you for your suggestions.  I lost 2 the first year and thought it was because they did not get enough water  or some afternoon shade.  Will try again this year.

Great discussion on microclimates and the heat island effect; in my case most of my block fences are somewhat shaded, but not all. But it is my large back concrete patio, facing east that heats up too fast on summer mornings. I did not build this patio and if it were easy I would remove ½ of it. But consider concrete block fences versus other alternatives from a sustainable viewpoint.

Concrete is made from finite resources such as Portland cement, lime, sand and gravel. The process of making portland cement uses a lot of energy to cook the material. The weight of block requires more fuel to ship.

Wood fences are a good choice as wood is renewable. Hopefully the wood comes from a sustainable forest; something to look for. Wood is a good insulator so will not heat up as much.

Chain link is made from steel. Though steel is not renewable it is highly recyclable. Over 90% of the steel in the US is recycled. The fence itself will be over 90% of recycled content. So aside from the performance of your fencing; if you are fence shopping, consider the embedded energy of the materials in your new fence. Yes, plants make the best screening and fencing.

Excellent points, Patrick!

I would add if anyone is thinking of putting up a wood fence to use metal instead of wood posts.  Wood posts tend to rot out over time and then your fence becomes unstable (falls in on your property or over on to your neighbor's).  By having metal posts going into the ground, your whole fence lasts a LOT longer.

There's also "waffle" fencing that allows airflow through while maintaining a high degree of privacy.

Or there's lots of fun ways to use bamboo for fencing - which is somewhat common in some older neighborhoods, especially those with flood irrigation.

In places (like here) where there's an abundance of palm fronds, panels made from the leaves (we called them "makuti" in Kenya) are layered to form thatched roofs and fences and are very beautiful.  They have the added benefit of having high insulation value.  They've also been found to trap and channel condensation.  So they could act as a kind of rehydration element as well.

That waffle fence is super cool! I really like it.

A living fence (Belgian or hedgerow) is the best of them all. Gets stronger with age.  Needs watering and pruning however.  But some sink deep roots and can do pretty good on their own after they mature.

Properly planned provides wildlife habitat as well.

pros and cons of various fences imho:

wood fences are cool, in both literal and figurative sense, but the drawback is that it is somewhat expensive, considering that  it warps and degenerates after several years of exposure to the elements. Sun, rain, wind, molds, and insects   make it less and less of a novelty as time passes. Asian teak is probably the only wood that will resist the aforementioned, aside from being dimensionally stable and warp-resistant. But the cost is prohibitive.

wire mesh is definitely longer lasting, but is not forthcoming(especially when not tightly fastened) in appearance unless concealed with plenty of flora. It also has the disadvantage of not being able to totally  block nosy neighbors, as foliage cannot possibly seal all holes.

wrought iron is way more attractive and just as longer lasting, but has the same privacy drawback as wire mesh, and is  even more expensive.

concrete block is also attractive, on top of which it offers total privacy, but as  mentioned, it is expensive, and its thermal properties have some disadvantages, especially with heat-sensitive plants. Painting it white would minimize heating of thermal mass, but concurrently, will   reflect more light towards sensitive plants and the house, so has disadvantages as well. Concrete that is painted also loses its 'timelessness', and ends up somewhat of  an eyesore  as paint  tends to be a sticky fly paper for dust, and gets stale after a few years exposed to the elements, needing vigorous cleaning/treatments before repainting, whereas raw masonry(in desert conditions) seem to  retain much of its color and texture even after several decades. A good drenching with water will dislodge dust and wash it down.

whereas the thermal disadvantages of block wall are noted during summer, its advantages are notable during harsh winters.

storing and reflecting heat will /delay plants freezing. And being opaque to wind, it will minimize  wind-chill effects.

Lots of good discussion here - thanks everyone!

For me, my decisions at this point in time would be based on permaculture ethics - earth care, people care, return of surplus. 

So if we define permaculture as "a design science based on living systems that can provide for all our needs" - fencing made from renewable resources such as wood are preferred.  Or even living fences made from prickly pear cactus or sustainably harvested ocotillo.  Even a grapevine wattle fence is possible with enough material. (in a different climate, I have woven wattle fencing from the trimmings of pollarded mulberry trees).

Next would come locally sourced products that we can repurpose, like fieldstone in certain locations, and fences made from recycled materials, like metal.

Last would be fences made from non-renewable or non-recyclable materials, or from materials that have a high carbon footprint to manufacture.

I vote for no fences!... ... ... ... and no neighbors!

LOL.  There have actually been several studies on the detriments to the overall community when impervious fences/walls are erected between neighbors.  Apparently this leads to diminished communication and a fragmenting of the social fabric.

There have been times I've wished for no neighbors.  However, I am SUPER lucky to have amazing neighbors on all sides of me, which has been a boon to me as I have not driven for 8 years now.  I don't think I could do without my nabes!

Neighbors are cool when everyone is sitting on a few acres...IMO.

Yes, if I got rid of my immediate 5 neighbors, I definitely wouldn't mind the others... whoever they are. J/K, I'm one of the few around here that actually does know a decent portion of the neighborhood.

LOL.  Hey, knowing most of your neighbors is a RARE trait these days.  Good for you and keep it up!


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