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Gravel Gardening and microclimating

Gravel yard
I have just finished laying down a layer of cheap gravel over all of the front yard.Below that is weed mat.

The gravel is 20 mm drainage aggregate  so it won't be going anywhere in a hurry.

It has taken me some time to do all this but I have finished in time for 2011.

Since I will  replicate the same gravel garden approach at the back of the house, I have to wonder what I am doing.

Why stone over the grass?

That I positively despise mowing is the cheapest answer. Lawn mowing is  up there with the most wasteful of  spent energy.  And having to mow when you can't (as happens with me because of ill health) --or don't want to -- is a  a form of suburban oppression.

If you aren't going to use a lawn -- such as to play cricket upon its stems -- what's the point of having one?

In fact, in my outlook, a lawn is so many weeds clumped together.

But I am, if you excuse my pretense, a gardener. I value plants and manipulated ecology. So I need to make sense of my impulses to over rule verdant biology by suppressing it under stone.

Stone is as natural as dirt. It happens all over. And stone has insulating attributes that will protect rooted plants from the vagaries of the weather and retain moisture. Where I live now, the soil layer if it exists, is very thin as the earth is beach sand all the way down.

So gravel gardening is often used in my community as a means to protect  plants from the sieve that is sand. There is also  no reason here to build up garden beds for the sake of improving  drainage.

While a gravel coating will increase ambient temperature as the stones will retain and reflect heat , when the plants grow, the gravel surface will be shadowed  and a new dynamic is -- or may be -- introduced. So I reckon you need to plant to shade the gravel by using small tress, bushes and especially ground covers.  

Just like your stereotypical 'rock garden'. 

But here we don't go planting  desert vistas with succulents. Here we plant drought tolerant Australian natives (Grevilleas, Hakeas, Kangaroo Paws, and the like)-- and Mediterranean herbs (like rosemary and lavender).

So a gravel garden is a drought tolerant garden  where  the protective mulch doesn't rot away and shade is also deployed as a mulch element.

When I finished the front and began to ponder my backyard options I was concerned that I was  going to surround the house with a hot space zone. Shouldn't I be trying to cool the house by promoting more direct shade or a fostering a terrain through which any breeze would have its temperature reduced?

I've grown trees close up to buildings before in search of shading  and they only lead to blocked gutters, more mosquitoes and reduced internal light. They can also block the breeze when it blows. So I was keen to not only use stones but more or less treat the front and rear gravel zones as courtyards sparsely populated by plants with nothing whatsoever  in common with rain forest style.

And the more I looked at  the gravel template the more interesting and exciting it became. You can cool gravel by shading it. That's clear and the thermal mass of all those stones should have a certain  insulating reward ...if cooled. The bugs I hate -- the mosquitoes and sand flies especially -- are kept at also arms length from the front door  as stones aren't their preferred neighbourhood.

But the thing that really sparks my attention is the prospect that maybe -- maybe --  surrounding a house with stones here in subtropical South East Queensland may also reduce residential  humidity. 

Is that a possibility, do you think? Since the air has to travel across such a  dry surface area and one that doesn't in itself hold moisture -- maybe it will cause the air to lose some of its warm vapour? 

The related prospect is  how effective would be any sharp  environmental contrast between the temperature inside the house and the ambiance on the gravel gardens directly outside. What would be the consequence for air movement?
I recall that traditional southern Mediterranean and Arab house design use this contrast to good effect as a means of promoting air movement to cool houses. In Sicily houses  are not cooled by planting trees. Rather, thermal mass - through stone and cement -- is orchestrated to effect temperature reduction. And in Morocco etc, shade cloth and mesh are used to shade an outdoor space  rather than anything vegetable. In Spain, a courtyard will often have  a pond or fountain in order to moisten and cool  the air but the rest of the space will be stone or cement.
If I could make the air both cooler and drier over the gravel zones then I am ahead of simply making the air cooler if I were simply to rely on grass. 

I'm not being rigidly schematic here  as the other part of the design story is the contrast between organic and inorganic mulching. One of the reasons why I switched to using gravel in some areas was that I wanted to deploy any organic  material I could get my hands on to better effect mulching  fruit and vegetables. So outback, the 'inorganic' gravel zone gives way to a zone steeped in grass clippings, manure and the like -- any number of collected organic mulches.

So the pivoting part of the template is separating organic from inorganic mulching: inorganic vs organic zones and making the best use of both.




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