I also have a glass greenhouse, and it does get pretty hot in there...and i live in the north-east! It was recommended to me by another grower to use a product called 'liquid shade', its like a white paint kind of. It comes by the gallon, and one gallon makes about 10 gallons because you water it down a lot. You spray it on, or paint it one in early/mid spring, and gradually keep adding it as it gets hotter outside. It does wash off after heavy/steady rains i guess, but it is suppose to be relatively easy to apply. I haven't tried this yet, but i plan on doing so next season. I am unable to use shade cloths since they need to be placed on the outside of the house. Doing so wouldnt allow me to open my ridge vents, and if you put the shade cloths up inside the GH you actually create more heat on the inside because the dark shade cloth absorbs the heat.
Do you have any type of cooling system in your GH?

Um, sarah: Wrong about the shadecloth. If you use aluminet and lay it so the stretchy part run from top to bottom, the roof vents open under it easily and as a bonus, the aluminet gives you insect screens for the vents.

It beats pouring whitewash all get out, and is far better at reflecting the heat of the sun away from the GH.

I was concerned that the corners of the vents might tear the aluminet, so mounted some self stick foam pads on them. Worked like a charm.

The buggar of that was discovering that the shadecloth made screens AFTER we constructed nicely framed fiberglass screens to fit the roof vents. (sigh)

Sarah,
I have 3 roof vents, and will add a fan and misting system. Is 68% enough light transmission? Or should I just stick with the shades?

Well...70-75% available light is the optimum range for plants. If that helps!

I'm in southern CA, too. My greenhouse really heats up in the summer so I hang shade cloth over it from May through November. The vents and fans just aren't enough. I even built a raised bed in front of it and planted citrus trees to create shade.

Here's what it looked like before the shade cloth:

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With shade cloth:

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It rarely gets over 100 degrees inside in the summer now.

Cagary,

That's a good looking greenhouse, what are you growing in there?

Im envious. What a setup. That is nice cagary...... Barb

Cagary,
Nice GH, where did you get it from. I'm moving from South Florida to central Tennessee, and I am looking at something like that, a 16x20 from BC Greenhouses. Your's looks bigger.

Cagary,
Nice GH, where did you get it from. I'm moving from South Florida to central Tennessee, and I am looking at something like that, a 16x20 from BC Greenhouses. Your's looks bigger.

Mine is a little bigger at 17x37. It came as a kit from BC Greenhouses. As you can see in the photo, I built it on top of a concrete block raised bed so I would get a higher ceiling. It doesn't have a floor; the plants inside grow right in the ground.

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I grow all kinds of tropical plants from fruits like papaya and Mountain Apple:

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To flowers like Heliconia and Jade Vines:

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Very interesting looking plants Cagary. That Jade vine is rather interesting. Thanks for sharing the photos.

Very nice. Do you leave the doors open for any pollination?

jay,

There are vents in the ceiling that open automatically when the air warms up, so bees and other insects could get in to help with pollination. but the fruit plants I grow are self fertile or I have to hand pollinate them. My Atemoya (Annona squamosa à A. cherimoya), Soursop (Annona muricata), Ilama (Annona diversifolia), Custard-apple (Annona reticulata) and Sugar Apple (Annona squamosa) trees have to be hand pollinated because here in California, we don't have the right insects. The Cherimoya trees I grow outside have the same problem.

The papayas all have hermaphrodite flowers meaning they have both male and female characteristics so I only need one plant to get fruit.

The Mountain Apple (Syzygium malaccense) tree fruits like crazy. I never see any insects around the flowers so maybe it is self fertile, too.

Cagary,
That is one beautiful greenhouse! And the tropical plants are certainly amazing too!
I have summers that get to 110 outside for a month. I used clear polycarbonate which is nearly like glass. My custom greenhouse is only 10 x 12, with no vents. I just use one attic fan to pull enough air through the greenhouse, set on an automatic timer, and a mister by the window in the storm door I have as a door (works like a swamp cooler with only a mister), and I never have inside temperatures over 100, as I monitor it daily with a remote min/max thermometer.
I do admit with all that bright light it may be tough on tropicals. A few orchids and a few fuchsias have to be set behind other plants so that they get a bit of shade.

I love the greenhouse. It looks so nice and roomy. I have a jade vine in mine. How long did yours take to bloom? I'm trying to decide if I should leave it in the greenhouse full time, or take it out in the spring. It doesn't really freeze here much.