The question has been asked whether or not the height of greenhouses should be greater in warm climates – to allow for better/more air circulation. The short answer is no.
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The height of the structure does not reduce air circulation. The continuous ventilator along the entire roofline of the permanent seedling greenhouse lets hot air escape quickly. Also, in warm climates the plastic on both sides is designed to roll up , to give excellent side ventilation.
The height of the structure was chosen to accommodate standard lumber lengths plus the reach of most gardeners. Seven feet is about as high as most of us can reach comfortably.
It’s also about the same height that tomato plants will grow before we cut the tops off 8 weeks before the first expected frost in cooler climates- where tomatoes and other warm weather crops are most likely to be grown in greenhouses – so they can mature all the fruit they have set.
For longer growing seasons such as in Central & much of South America, Africa, the Pacific Islands, and the Caribbean, let the plant turn over and come back down, rather than cutting it off. This will require pruning leaves off the lower branches when fruit has been picked.
The in-the-garden greenhouse would be built the same in hot humid climates as in temperate zones, the way it shows in the YahooGroups pictures, except that you don’t keep the plastic all the way down except during a bad storm.
Rather than protecting plants from cold weather and frost, in warm climates the in-the-garden structure is mostly used to keep heavy pounding rains and hot direct sunshine from hurting tender plants.
In warm climates – and during mid-summer in temperate zones – I recommend you roll the plastic up to the top on all sides and tie it in place.
For additional shading if needed during the hottest part of the day, consider either throwing a 30-40% shade cloth over the top, or if the shade is needed for a long period of time consider splashing white-wash on the under side of the top plastic. Use material that will wash off when water is applied.
For more information on building and growing in greenhouses visit the archives of the Gardening Group.