What inside temp was your greenhouse with the 95F heat wave we just had?
Interesting timing on your post. I got a lovely small greenhouse 2 years ago from Backyard Discovery. Living in the deep south, obviously this is a cooler weather greenhouse only. It was 96° yesterday and the greenhouse got to 114°, at least when I checked it.
I finally turned off the fan yesterday, all I was doing was wasting energy and wear on it by running it during the summer with no plants inside. I store a lot of outdoor items in it.
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Does the fan do much good to cool it down?
My dream is to get a greenhouse. But I have no idea how they will work for me. I just know 95F and humid and it is unbearable outside without the greenhouse.
Not down here no, the fan doesn’t do much in summer at least. The two windows opposite and the two low louvers along with the fan don’t do much.
But that is the design of the kit I bought. You can buy thermal wax activated louvers to install on the roof which would go a long way to approaching ambient.
For my rather closed in greenhouse, I have actually thought of adding an AC. If I could find a small unit that I could set the thermostat at 85-90, I’d give a try. In my brief look, I did not find one.
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In a dry climate a wet wall and large exhaust fans can hold inside temperature at or below outside. In a hot humid climate shade cloth and high ventilation is your friend. A greenhouse needs one air exchange per minute to hold inside to 15F of outside. Natural ventilation can do that if there are big openings high up to vent hot air and low down to let in outside air. Large exhaust fans can also do that. My 1725 sqft GH needed two 36 inch exhaust fans for ventilation during midday in summer.
Most greenhouse are woefully under equipped to handle high heat loads, Thus, most become seasonal tools. Like any tool they only work well when properly designed for the task at hand.
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Fruitnut, Any thoughts on the use of roll up side walls vs a wet wall as far as cooling in the summer?
A properly designed wet wall will keep a GH cooler, and more humid, if the dew point is below 65F. Above 75F dew point a wet wall is pretty useless. A greenhouse with roll up sides will always be hotter inside than outside. For crops like citrus either will work. They’ll take humidity and high heat.
The thing I worried about with exhaust fans and a wet wall is a power outage on a hot sunny day. In 20 years that never happened. Natural ventilation doesn’t have that risk and is cheaper. For citrus I’d go roll up sides.
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July and August dew point is around 70. I will be using half my space for citrus and the other half for peaches and nectarines. I suppose having both would provide non identical benefits over time and in different seasons.
That would be hell covering the rood with shade cloth. I thought I could grow figs in it year-round in pots. (Originally I was going to plant 5 or 6 in the ground figs in the greenhouse.) But I guess the green house would only be good for getting an early start with the pots and moving the figs outside in the hot months. And for extending the season in the fall to get the last of the figs when frost hits.
There is a guy in central Texas growing in high tunnels with figs and citrus in ground without much of a heat issue it seems. He has raised sides.
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Both figs and citrus are very tolerant of high temperatures. I’m guessing his tunnels hit 120F at times. He, Little Bexar Farms, also seems to avoid cold injury in winter without supplemental heat even when it drops into the teens. Maybe you have more insight about that end of the temperature picture. His videos haven’t been very enlightening on that subject.
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I didn’t see any propane heaters. He did mention that the gravel pathways are a heat sink and help moderate the temperatures. I’m going to have a follow up conversation with him soon.
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I watched his videos last night and he says he uses no heat. He relies on the stone to emanate heat. In 2021 we had three days of temperatures slightly below zero degrees and he had some damage to a few trees mostly on an outside wall adjacent row, but nothing major. In his earlier greenhouse he used concrete blocks for the beds instead of gravel. He said the gravel is better
