how much water does a typical greenhouse need per square meter of crop grown?

Question

I just want to get an idea of how much more intensively a greenhouse water use is compared to growing the crop outdoors. Ideally I am looking for examples from greenhouses located in the northwest pacific region or at least in canada. Any help with this will be much appreciated!

Answer 1

The first two answers are correct. However there is something that can be said even without more specific information.

I grow orchids in a greenhouse in California.

Greenhouses located in the areas you mention especially will require quite a bit more water than if the crop were planted outdoors. The reason is threefold.

1) The interior of the greenhouse will be significantly warmer than the outdoors. Water will evaporate faster the warmer it is.

2) The humidity inside the greenhouse will be lower than outdoors. That will also increase the amount of evaporation.

3) It is a good idea to have a fan to circulate air in the greenhouse. The fan should run continuously or at the very least in the daytime. It will reduce pests and plant diseases, however moving air will also increase evaporation.

The relative humidity in a greenhouse can get quite low even in an area with high outdoor humidity. That can be a problem for plants and can encourage some kinds of pests and may need to be offset by using a mister, but as I note below avoid a very high humidity.

Evaporation can be suppressed by maintaining a high humidity using a mister for instance inside the greenhouse but that can be a bad idea if the humidity is much above about 50%. High humidity will encourage plant diseases. Also at night when the temperature falls the humidity will reach 100% causing dripping onto the plants, which also causes disease.

While I cannot say with precision how much more water you will need in a greenhouse, it will be more and will probably be more than twice as much.

One final note about greenhouses. Avoid temperatures above 95F. For most plants photosynthesis shuts down above that temperature, which will stunt the growth of your plants. Your greenhouse will need vents at least that can be opened and closed, preferably automatically to reduce temperature and may need active cooling using fans or a swamp cooler.

Answer 2

as a civil engineer we study crops, yes, odd, but we do so we can plan infrestructure. To be honest, I don't know much about greenhouses, but I can tell you, that you have to be more specific on the area where you'll be growing, and what type of crop. The type of crop is crucial, since it depends on what plant or plants will you have, to be abble to calculate the amount of water needed.

Answer 3

it also depends on some other factors like climate, nature of soil, which plants u r talking about & inner climate of that green house, this is a matter of further study & research in this imp. subject. thanks for asking.