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bower · July 15, 2015

Steve,

I did a google for "goldilocks temperature tomato" and found this - see post #7 by FusionPower which gives detailed information about tomatoes and temperature.
http://forums.seedsavers.org/forum/g...p-for-tomatoes
The temperature where blossoms begin to drop is 92F. In my greenhouse, I can only measure temperature in the shade, because direct sunshine makes it read in the hundreds. For me, temperatures above 80 F in the shade are correlated with the temperature in direct sun where blossoms drop.
One very important question is the type of glazing, and the height above the plants. As regards the height, more head space is better, and if ventilation is designed properly the air flow through the higher and hotter part should cool them.
As regards the glazing, plastic is better than glass. When my greenhouse was rebuilt, we picked up some second hand double glazed glass panels and used instead of plexi or plastic. I didn't know then what a difference it would make. The plastic normally used for hoop houses or high tunnels has a big advantage for plants, because it diffuses the light. Best quality greenhouse plastic is also uv resistant to extend its life cycle. I have read UN reports that looked at the effects of higher UV on crops and concluded that the effects are deleterious for fruit crops including tomato. This is consistent with the response of tomato plants in my greenhouse when the UV is high - they wilt in response to the stress regardless of water status, more especially if we've had a run of days without sunshine and then suddenly it's bright and hot with UV 7-8. If the weather is more consistently sunny, they adapt to it after a couple of days, but if they are already close to the glass it's too hot for the blossoms anyway, at least for most varieties, even at shade temperature readings in the 70's.
50% shade sounds like a lot to me, even for a sunny day under glass.

I tried using row cover for shade one year... it was difficult to put it up, but as soon as I did so, the weather changed, and we had the coldest and most unsunny July ever while my plants huddled in the dark.

What is your greenhouse like?

July 15, 2015	#5
bower Tomatovillian™ Join Date: Feb 2012 Location: Newfoundland, Canada Posts: 6,793	Steve, I did a google for "goldilocks temperature tomato" and found this - see post #7 by FusionPower which gives detailed information about tomatoes and temperature. http://forums.seedsavers.org/forum/g...p-for-tomatoes The temperature where blossoms begin to drop is 92F. In my greenhouse, I can only measure temperature in the shade, because direct sunshine makes it read in the hundreds. For me, temperatures above 80 F in the shade are correlated with the temperature in direct sun where blossoms drop. One very important question is the type of glazing, and the height above the plants. As regards the height, more head space is better, and if ventilation is designed properly the air flow through the higher and hotter part should cool them. As regards the glazing, plastic is better than glass. When my greenhouse was rebuilt, we picked up some second hand double glazed glass panels and used instead of plexi or plastic. I didn't know then what a difference it would make. The plastic normally used for hoop houses or high tunnels has a big advantage for plants, because it diffuses the light. Best quality greenhouse plastic is also uv resistant to extend its life cycle. I have read UN reports that looked at the effects of higher UV on crops and concluded that the effects are deleterious for fruit crops including tomato. This is consistent with the response of tomato plants in my greenhouse when the UV is high - they wilt in response to the stress regardless of water status, more especially if we've had a run of days without sunshine and then suddenly it's bright and hot with UV 7-8. If the weather is more consistently sunny, they adapt to it after a couple of days, but if they are already close to the glass it's too hot for the blossoms anyway, at least for most varieties, even at shade temperature readings in the 70's. 50% shade sounds like a lot to me, even for a sunny day under glass. I tried using row cover for shade one year... it was difficult to put it up, but as soon as I did so, the weather changed, and we had the coldest and most unsunny July ever while my plants huddled in the dark. What is your greenhouse like?