Author Topic: Plants for unheated greenhouse  (Read 852 times)

vnomonee

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Plants for unheated greenhouse
« on: February 10, 2023, 02:27:36 PM »
I am building a small hobby greenhouse, it will be unheated and will have 2 automatic venting windows and perhaps a solar powered fan.

Can I plant a small flying dragon inside with poncirus hybrid grafts and keep it inside all year? Will the temperature extremes in the winter kill the tree? How about a feijoa/pineapple guava.

My concern is with the sun shine in the winter it would bring the greenhouse way above freezing, but then night time plummeting to freezing again  Will this kill the plants long term?

kumin

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Re: Plants for unheated greenhouse
« Reply #1 on: February 10, 2023, 02:55:10 PM »
I have used a similar set up for the past few years. White overwintering plastic film reduces daytime solar gain. It's very important to prevent excessive heat buildup to prevent the formation of  tender, new growth. A small emergency heat source may save vulnerable trees on the few, out of ordinary cold nights. It's again important to not overdo this emergency heating.
Night time temperatures can be below freezing without harm if the plants are dormant. venting needs will largely be determined by the amount of sunshine. Trees planted directly in the ground will not be as vulnerable as potted trees. Slightly moist soil will retain more heat from day into night, especially during sunny days.
Further tweaks include insulating between the inside and outside soil at the perimeter, using water barrels as heat storage sinks(this can be a disaster if the water freezes).
There are also seasonal white shading sprays that can be applied to rigid plastic and glass surfaces to reduce solar gain.






« Last Edit: February 10, 2023, 04:22:13 PM by kumin »

Tropicaltoba

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Re: Plants for unheated greenhouse
« Reply #2 on: February 10, 2023, 03:33:26 PM »
There is a good resource from the university of florida on greenhouse design. There is a mathematical curve comparing air exchanges per minute with inside air temp. Not sure if this helps. https://edis.ifas.ufl.edu/publication/AE030z I used it for my 4 season greenhouse and it is very accurate.

Nick C

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Re: Plants for unheated greenhouse
« Reply #3 on: February 10, 2023, 04:28:42 PM »
I keep Xie Shan satsuma, citremon, yuzu, and pineapple guavas all in ground under a poly tunnel throughout the cold months. Temperature swings have never been an issue. I don’t even open the sides on days in 50/60s

vnomonee

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Re: Plants for unheated greenhouse
« Reply #4 on: February 12, 2023, 08:32:21 PM »
Thanks everyone appreciate the input

1rainman

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Re: Plants for unheated greenhouse
« Reply #5 on: February 18, 2023, 09:22:43 AM »
Water moderates temperature. It will absorb heat in the day cooling it then release heat at night. Plants do the same to a lesser extent. Large buckets or tubs of water can mitigate the day night extremes a bit. You will need some kind of window or door to leave it open during the summer so it doesn't cook in the summer but winter won't have much sun up north so shouldn't be much of a problem.

Florida has a lot of sun even in winter so yeah down south you might need to block sun. New Jersey in fall, spring, winter I don't think so.

vnomonee

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Re: Plants for unheated greenhouse
« Reply #6 on: February 18, 2023, 01:18:56 PM »
Today was a real test since it's very sunny. I found that I have to glue the panels in place as two were blown out in the yard this morning despite using the supplied clips to secure them.


Outdoor temps:


Inside greenhouse with the windows closed:




kumin

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Re: Plants for unheated greenhouse
« Reply #7 on: February 18, 2023, 02:46:06 PM »
Unvented Cold frames with clear glazing can get very hot even in the Mid-Atlantic states by mid-February. Although the outside temperatures are cold, the sun angle at this latitude allows the interior temperatures to rise to dangerous levels. Proper venting, or shading with opaque materials can be a solution. Allowing temperatures to rise to a high level will leave plants very vulnerable to nighttime lows below freezing. As trainman suggests, having thermal storage can reduce the daily highs as well as the nighttime lows.