No doubt in the South greenhouses become hot houses. I have one plant in there 24/7 , a pothos. It is old with long vines. I feel sorry for it and may eventually take it outside in the summer months. It gets so hot in there I dread using the potting bench inside. I do have a portable a/c unit in there i rolled in 3 years ago for when I get really serious about repotting. In the end, I only get serious about potting in early spring and fall. Whew! HOT!
There are some really good photos here. someone from FL (name?) erected amazing looking shade clothes. And on Pintrest of sun sails that block the summer sun and can be taken down for winter. I think that is just about all you can do?
https://image.made-in-china.co...
http://backyardgreenhouses.com...
