Using Plants For Airconditioning

After my first, incredibly hot summer in a weatherboard house with no insulation, no air-conditioning, and not even very good ventilation, I knew I needed to do something very quickly to shade the western side of the house, which bears the full brunt of the afternoon sun. Most old houses and even many new ones have not been designed to according to the climate and conditions, to passively heat and cool the home.

But using plants is an effective and affordable way to provide natural air-conditioning. A range of plants can fit the bill: if you have space you could plant a fast growing shade tree such as acacia, or an edible like mulberry. Or if you have a really large space something like a poinciana provides wonderful shade and beauty.

If you do not have much room a strong pergola or trellis allows climbing plants to scramble up. There are an enormous variety of climbing plants, some with gorgeous flowers like wisteria and clematis, others bearing fruit like passionfruit and kiwi. You can even espalier fruit trees like stone fruit, apples or pears – although you will not get shade quite as quickly as these take time to grow big enough.

I have a narrow strip of concrete down the western side of my house, with a half metre width of soil next to the fence. Luckily for me my partner is extremely handy and very keen to do things around the house – he built a pergola that attaches to the house right at the top under the eaves, so as to shade the entire wall.

So what plants could I use? Well, any plant that climbs or scrambles can be trained over a trellis or pergola. Top picks for me would be wisteria, clematis, pandorea, hardenbergia, jasmine, passionfruit, grape or kiwifruit. Vine vegetables like pumpkin, cucumber, melon, choko, loofah and trombonccini can also be used to climb up and over a trellis: bear in mind that annuals will need a lot of training every year but perennials will be more or less self-supporting once they are established.

My choice was based firstly on it being a deciduous plant – an uninsulated weatherboard house may be hot in summer but it is very cold in winter! I needed a plant that would drop its leaves and let the sun and light in during the colder months. That meant most natives were out.

Secondly it should be fast growing – I did not want to put up with too many more summers from hell. I needed to cover the pergola within a year or two at most.

Thirdly, this is a food forest so I wanted something edible that I like. Passionfruit, although probably the best as a subtropical fast growing climber, is not my favourite. It is also not exactly deciduous, although it can be pruned back over winter.

Finally, it had to be something that would do well in this climate so as to be as low maintenance as possible. A plant that was not suited to the subtropics would just create more work. I love kiwifruit but I know they like much colder winters than we have here – the chances of producing a reasonable amount of fruit were slim. Also, you need a male and female kiwi fruit and I have been told it is sometimes hard to know what young plants are.

Grapes were the obvious solution, providing shade in summer and letting light and warmth through in the winter. And who doesn’t love that Mediterranean, lazy summer look of grapevines?

I chose Sun Muscat, a white seedless sultana grape, and Autumn Royal, a black seedless grape, and put them in. They grew very quickly and within a couple of years had thick sturdy trunks on them and were quite self supporting.

Mid-Spring – not quite at their peak leaf yet

And they are doing their job – they make a significant difference to the temperature inside the house. On a hot day, as soon as you walk underneath the pergola the temperature cools by at least five degrees; it is like a cool oasis against the western wall.

I did actually end up putting two passionfruit in to cover the fence and I have pruned the grapes so that they begin their leaf and fruit above that. Grapes generally need pruning in winter as the fruit grows on new wood – however since I planted them primarily for shade this is not so important for me – I just want them to grow across the top of the pergola. Of course I do prune them back a little in winter, keeping the main branches and stems of the structure. This will be their third year – I pulled the fruit off last year to allow more energy to go into their growth, but this year I have some grape bunches and will harvest them – if I get to them first!

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