Shadecloth? over or under greenhouse or..........

Little Rock, AR

My GH was 149 degrees at high temp yesterday (real temp high was 70) and now question whether I put the GH in the right spot as it is getting baked before the leaves are on trees and the west sun is brutal. Needless to say some cilantro and a few other specifics fell out from the heat.

Will upload some picks when i can get a shot, but it is a 8x16 greenhouse w/ a back window and front door. I have now built a big deck around the whole thing and then started on some new beds. Changing the locale of the garden from previous years spot & GH is new as of last fall and must say i am on the learning curve big time. Have put in an auto timer mister system (3gph misting nozzles) throughout.

I've got to cool this thing down, it's an oven - so thinking shadecoth, but was wondering if it is best to buckle the cloth over the GH, part of the GH, or inside the greenhouse. I know my questions is not specific and w/o pix maybe difficulty to give me advice. I probably will get some auto windshield shade to totally reflect the west sun on the back potting bench.

Calgary, AB(Zone 3b)

Greenhouses need vents and air exchange fans even in his cool summer climate, so I wouldn't imagine you could do without them there.

Edit: Should be "this cool summer climate".

This message was edited Apr 2, 2013 8:44 PM

Ayrshire Scotland, United Kingdom

Hi Young_Buck, the best position for a freen house used to be with the roof ridge running from North to South, this was to help good light early spring and Autumn also, the intense heat of the sun on glass is quite un-believable at times, even here in UK where we dont really experience LONG periods of very hot weather.

To cool my greenhouse down in hot weather, I use the garden hose to spray the floor as this helps humidity and cools the flooring down, I have to at times throw over my benches where the trays of plants are sitting, the white horticultural fleece that is sold in either per metre or as a bundle, this stuff is as light as a feather so wont harm the plants but it prevents the reflective heat hitting the tender plants, another thing I sometimes have to do is fold large newspapers and tack them against the window glass and this helps prevent the sun burning the plants, all this wont prevent the heat build up inside so perhaps you need to make more opening windows, you need openers on the glass roof also and doors and all other windows that can be opened. IF you can have electricity put into the glass house (well away from water) this electricity will allow you to set up a fan that will move air around the G House, it may not cool it down but by moving the hot air about it may prevent mould ect to take hold.
Here in UK, IF I was having to cool my house down to the extent you are then I would make a bench of wooden planks lifted up from the ground by bricks or something, place the plants inside the greenhouse out onto the new bench and either take them back in at night or cover the plant trays / pots etc with the fleece, to keep any night coolness off the foliage and also prevent night feeding insects away,
Hope this helps you a little.

Contra Costa County, CA(Zone 9b)

Put the shade cloth OUTSIDE the greenhouse.
Start with it covering perhaps 25% of the roof, maybe the peak to western eaves.
If that is not enough, then cover the rest of the roof.

Another way is to get a lighter shade cloth now, perhaps 20-25% reduction in sun, and place it all over: Roof, south side, western side, maybe also eastern side.
As the sun gets hotter buy a denser shade cloth, maybe 50%. Take off the lighter one, put the denser one on.
Then, when the sun gets the hottest, use both together.

Altagardener is exactly right: Green houses also need vents, and even fans to keep cool.

Around here (just inland from San Francisco) it is common to paint greenhouses with whitewash. Auto fans and mist systems are popular, too,

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