September 3, 2014

Make your own greenhouse – a microclimate in your backyard.

If you have a spacious backyard you may like to build an actual greenhouse which will create a reliable microclimate for propagation, nurturing tender and out of season plants. There are many models on the market for Aussie backyard use, a good suburban size being 3m wide x 4m long and high enough for you to walk in. Some of the smaller models may be OK for propagation, but I have seen these blow over and disappoint their owners.

Google ‘greenhouse design’ and you will find umpteen patterns for a DIY or find enough pictures to adapt for your own needs. They are best built with walls sloping outwards to catch the maximum amount of light and a glass roof. Glass or plastic walls, from ground to roof, makes orientation unimportant. But maximise exposure to light by not siting it in the shade of a tree or a building.

A well-designed greenhouse needs to store heat and re-radiate it at night or you will need to heat it and then it becomes not such a good deal. Increase thermal mass for heat storage by using 44 gallon drums full of water or breeze blocks as bench supports. You can even build a cyclone wire frame and fill it with recycled concrete topping it with a shelf of concrete. Some large systems have compost bins and soil containers under the benches, making the most of their heat.

Horticultural glass diffuses light perfectly. PVC is a cheaper alternative but rots fast and a double skin of whatever you use improves heat retention.

Floors can be gravel or recycled concrete (easy to source and some brick factories give away their broken bits as well) sloped for drainage. Wetting down the floor helps maintain humidity. Benches and shelves will maximize your space, but always look at where you are creating shade. Cyclone wire is a good thing, as air can circulate. Browse your local tip for cast-offs!! Or hard garbage collection days go for a cruise!

Ventilation is important as the warm, still air in a greenhouse is the ideal breeding environment for many moulds, pests and diseases. Ridge line ventilation works well, warm air keeping the air moving when open or closed. Close on cold nights.

Shade cloth is essential in the bright heat of Australian conditions or you can white wash your glass as a diffusion technique applying a new coat each year.

Your greenhouse can also just be large hoops (old bits of water tank) covered with strong poly which is not just stapled or riveted on but also anchored with some strapping to keep it on in windy weather.

If you don’t want to have a greenhouse in the garden, you can create a microclimate with plants by being very savvy about what you can plant against walls – for instance, the north and eastern faces will absorb and reflect sun in the mornings, while the faces on the south and west will be more shaded then and the opposite in the afternoon and may then need protection. The sun from the west is a killer at the moment.

Courtyards and buildings that surround planting areas on three sides can be used to catch sun and avoid wind for winter planting areas but may bake your plants in summer.

If you plant fast-growing nitrogenous trees such as wattles to provide wind and sun protection for the first few years or hedges, you will give whatever is planted next to it a fine start. You can pull out the wattles later if you like. The protection that you have will create a nice little area for plants such as camellias. Or if you want, you can plant peas or lettuce in the centre as long as you get some sun in the morning till around 2 pm. Airflow is important.

If you have a white wall, you can grow tomatoes in front of it.

The reflection will make tomatoes grow well as long as you don’t water the leaves. Support from the wall will be important too, and you will find that the funguses do not spread as well because they are always clean and dry on one side. Blood and bone is also essential for strong growth. You can get the same effect by putting white painted rocks around any plants you think are best suited to a more northerly climate.

Planting shade trees is a good strategy and plants that are not so hardy can be planted beneath (ferns etc.) as long as you continually build up your nice, rich humus.

Instead of having a lawn in the sun, choose a shade mix, put the grass in the shade and turn the old lawn into an all-year vege garden, rotating your crops to keep the soil sweet. A light-coloured mulch will also reflect heat onto your plants. Position bales of straw around heat-loving vegetables like all the members of the poison ivy family – eggplants, tomatoes, spuds and chillies as a protective wall and then as it rots, move your garden to that position and place the bales where the old ones were . A Torquay friend of ours actually built his ENTIRE massive vege garden from hay bales and used barriers of bales on the perimeter as a wind (and kangaroo) barrier, again, digging the hay in as it rotted and replacing it.

A microclimate just needs you to think logically, providing ample shade or sun for the plants you want and being consistent about the plantings within the territory. I had friends who grew avocados, pineapples and paw paws in Tassie (with FRUIT) but all because of their assiduous attention to Bill Mollison’s idea of Permaculture which is a system based on the creation of microclimate, key-lining of dams and planting for compost, fruit, shade and timber in smart measures.

This system of building micro-climates and managing light and heat in your garden is simple and logical and very good for the environment. To say nothing of how great you feel when you harvest veges and herbs all year around, enough for you AND the neighbours!

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Comments

  1. Pollyn Lee says:

    Thank you, Wendy. Great ideas. Is it really possible to grow tropical fruit trees like the mango, paw paw, pineapple or durian in a green house in Victoria? Any advice you have will be appreciated.

  2. Hi there Polly,
    In theory, yes you can do it. Some people I know even grew avocadoes in Hawthorn. You just need to give the correct balance of water as mist and on roots, feed well and ensure high temperatures. Burnley Ag College is a good source of advice on this. Some hints include, 1. grow against a white brick wall that attracts the sun and keeps the heat in 2. Mist the foliage often (in the early morning but not after 2 pm or you will get mould 3. Companion plant to make a micro-climate. In greenhouses this should also be tropically regulated. The Botanical Gardens also can help. When you have your first Durian, please do not take it into hotel lobbies, buses, trains etc.. Ha ha! I detest this fruit but one day must have another try to see if I can stand it. Good luck with your project and let us know how it goes. Send some photos. All the best,
    Wendy

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