Unheated Greenhouses

[frustratedearthmother]

That's great and I'm laughing my butt off because I almost mentioned to you the other day that you should save all your bubble wrap and tape it up. I had no idea it's really a thing, lol!

 

[R2elk]

@R2elk I love your greenhouse. It's even a great winter porch area!! I've been wanting to enclose my back porch in a similar way. Morning sun on back and southern exposure on end. Those pictures just spark my desire again. Dang you!! 🤪

My porch is a 3' raised, sand filled, brick outer and concrete poured on top, for the floor surface. Sounds like a heat sink storage area. 🤔 wood rails and posts. I think there's possibility!

The outer panels are triple wall polycarbonate with a 1/2" space between the outer panels and the inner twin wall panels. The roof is corrugated polycarbonate panels with polycarbonate sheets on the bottom of the rafters. They were added later to create a dead air space for insulation purposes.

The proof that the roof dead air space works is that snow can be on the roof and the temperature in the greenhouse can be in the 80°s without the snow melting.

A fan driven ventilation system is a requirement. Without it the summer temps will be unbearable.

 

[R2elk]

Greenhouse has been doing well holding nighttime temp 46 - 50 degrees F when we have gotten as low as 28 degrees. This next week will be interesting test. We will have progressively colder overnight low temperatures, forecasted low next Friday is 18 degrees F.

The real test is overcast days with freezing temperatures preventing any daytime heat gains.

 

[tortoise]

Would a 100 w bulb in greenhouse be possible? I've read that just a candle burning in a car can keep temps up...

There is an extension cord out there, so yes. I'm not sure I'm willing to use electricity on it.

I got started too late. A book I'm reading describes a winter greenhouse not as extending the growing season but as extending the harvest season. The author harvests through December, takes January off and starts growing again in February. I think that schedule will work for me, but I should have started my leafy green trays earlier.

 

[tortoise]

Greenhouse hit low of 32 degrees last night. Outdoor temp was 11.

 

[tortoise]

I pulled trays out of the greenhouse today. It's been hovering just above freezing. It could hold out longer, but I want to stop worrying about remembering to uncover them in the morning and cover them up at night.

 

[flowerbug]

All a greenhouse does is increase the temps when the sun is up.

It has close to zero insulation, but it does help with protecting plants from wind.

If you want a greenhouse to hold heat then it needs to be partly sunk into the earth, proper insulated roof and proper double pane windows.

I have seen plans where the entire greenhouse is sunk below frost level, and I have seen other plans where you have something like infloor heating in the growing beds.

There are some creative things put there.

But for zone 4, in the winter time grow stuff indoors.

the other thing to consider is ground heat storage as you can use pipes and small fans to move heat in the winter and to get cool air in the summer. look up the youtube vids on the guy who's growing citrus up north.

for winter heating if there is any sunlight you want thermal mass capturing that heat as much as possible and if you have a way of putting up some solar hot water gatherers, some solar panels, small pumps and fans you can really capture a lot of heat that ways too. the nice thing about such a set up is that it only runs when the sun is up anyways so you don't need batteries, but if if freezes where you are at you want the system properly designed so that it either drains back to empty when the sun goes away or the whole thing is set up as a closed system and the fluids are anti-freezed - my own preference would be the first one since that can be simpler.

 

[tortoise]

The blanket pulled over domes at dusk is holding them about 10 degrees above outdoor temps. was overcast and only got up to 70 degrees again.

Greenhouse saved them from the first light frost last night.

I have a library book ready to pick up on Monday about using unheated greenhouse. I read the book a couple years ago and remember it being helpful, but I didn't try anything from it. I was trying to use it in spring and was surprised to have more difficulty with heat than cold.

 

[tortoise]

I laid a sheet of black rubber on the floor of my greenhouse. I hope it will absorb more heat and reduce evaporative cooling from the patio. It might reduce drafts at floor level too.

 

[tortoise]

There's a sad ugly pine tree that shades my greenhouse until noon. It only gets afternoon sun until 3. 🤔 I wonder if I can convince DH to cut it down.