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Tuesday, November 11, 2014

Desert Greenhouses Should Be Tall and Shaded

Q. We would like to grow vegetables year-round for ourselves and family unless it is too expensive. We have power (110) available and plan to do as much construction ourselves as possible. We were thinking of constructing the perimeter with a 3 foot high block wall and then enclosing the top with some type of metal hoop structure with a translucent skin. Inside the greenhouse, the floor plan would be 3' wide and 3' high raised planters around the perimeter, and a 3x3 down the middle. We are getting too old to be on our knees. We have water available on a timer. We aren't sure about the hoop structure or the HVAC. What do you think?

A. I am hoping you are already good vegetable gardeners. Jumping into greenhouse production without being a good gardener will result in failure. I would recommend that you don't even attempt it unless you have solid vegetable growing experience already.
Temperatures in small hobby greenhouses are very difficult to manage properly. Greenhouses in the hot desert should be as tall as possible to get the heat off of the crop.
If you are hoping to save money by constructing a greenhouse and growing your own vegetables, you won't. Those vegetables will be expensive.
On the other hand, they could be better quality vegetables if grown correctly. The reason I say could is because you can get some very good quality vegetables in many of the grocery markets at different times of the year.
I personally believe that you should try heated hoop houses first before you invest into a greenhouse. Inexpensive hoop houses will help you understand the management practices you will need to adopt to make growing vegetables under protected culture a reality in the desert.
Shade is important in the summertime in desert greenhouses.
Hoop houses allow you to start your growing season 6 to 8 weeks earlier in the spring and extend this season 6 to 8 weeks in the fall. Doing this allows you to grow vegetables all year long here.
In fact, you can grow vegetables all year round here without any hoop house. You will not be able to grow any vegetable you want at any time of the year but you can grow vegetables in their appropriate season.
There are a lot of things that are going through my mind that you could try if you want to build your own greenhouse. It is not going to be cheap. In the hot desert you want these houses to be as tall as possible to get the heat up and off of the crops instead of captured under the canopy or roof.
These houses have to have very good ventilation. They need to have at least one air exchange every minute so you need excellent ventilation. This is usually done with exhaust fans that are sized so that you get the correct air movement and ventilation in the greenhouse.
There are two exposures that I think will work for you depending on the type of greenhouse. The first is an east facing greenhouse that receives protection from late afternoon Sun in the summer months. The house is oriented North and South. This exposure would require a minimum of six hours of full sunlight during the summer months. In the winter months it is best to get as much sun as possible.
Hoop houses like this one covered in shade cloth can be a valuable ally for quality desert vegetable growing.
You could keep it cool enough in the summer months using a swamp cooler and a ventilation fan or fans pulling the cool air through the house.
An alternative for an east facing house is to construct the North end wall as a very large evaporative pad with ventilation fans in the South end wall. The west wall would be a solid, insulated wall.
The Chinese style greenhouse is a south facing greenhouse with the North wall a solid block wall that can capture heat during the winter months. Extending from the top of the North wall is a shade cloth of about 30 or 40% shade that shades the vegetables during the summer when the sun is directly overhead.
Plastic covered houses in Egypt.
In the winter months when the sun is at a lower angle the sun will shine directly on the vegetables. This greenhouse usually has a solid wall about 3 feet high along the east, south and west sides. Hoops or lumber is used to construct the supports for the greenhouse clear “skin” on top of this low wall. Ventilation is from the East to the West wall. The house is oriented east and west.how to make a greenhouse, 
I hope this helps you a little bit. Perhaps I should put together some classes but like I said, it will be expensive to build these. My recommendation is to start with the hoop houses.

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