Greenhouse heating

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1

Hey everyone,

I’m looking for some input on heating a small 86 foot plastic greenhouse.

This year we moved and this far I’ve been keeping my trees in an unheated balcony keeping temps around freezing all winter but now the best I could do for now was a plastic greenhouse, basically a large tent with window and door openings with zipper and velcro, for now.

I padded the interior walls with Buble wrap to somewhat stabilize the temps, but after a few nights of testing inside and out, there were about 2-3 degrees C difference, so I think heating is a must.

I’m in Europe, zone 5a according to plantmaps, though, I haven’t seen those extreme negative temps in a few years, we do get the occasional -15-20 C.

The house is next to a stream so the weather is a bit colder then the surroundings.

Heating would be electrical, either a blower or heating cable tied around or under pots or on a heatbed with sand, hooked up to a thermostat set to around freezing or -2-3 C.

As for trees, I got maples, bald cypress, pines, junipers, stewartia and a lot of other deciduous, some more sensitive then others.

Which would you recommend?

Thanks!

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It is most important to keep the roots from getting too cold - the tops of most of our trees can handle much colder temperatures than the tops. My greenhouse is 0.006 inch (0.15 mm) plastic, bubble wrap with the bubbles against the plastic, and a layer of 0.0003 inch (0.0076 mm) film about 2 inches (5 cm) inside of that for a 10 x 25 ft (3 x 8 m) structure. I keep it at just above freezing using a 1500 W heater until the temperature drops to about 10F (-12C) when I have to add supplemental heat. I heat the entire greenhouse because I have trees on benches. If all of your trees are on the ground, the use of a sand bed with heat tape or other under the pot heating would use less energy. Remember to insulate below the sand/grit bed and to control the temperature close the freezing so you don’t get too warm and start growing too soon. I bury the pots to their rims Of course, you can increase the temperature up to 40-45F (5-8C) in late winter / early spring to jump start the season.

3

Thanks Marty,

Yeah, roots are the problem.I have some antifreez textile to cover them, that might also help, when temps are super cold. Yeah energy prices are way up over here so the tape or cable would be a sounder solution and if we hit an ice age I have a basement, though it’s pretty warm and carrying 50+ trees up and down with some heavy ones wouldn’t really work.

How high is you’re structure, guessing a lot of heat just rises to the top and that’s it.

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I was thinking of laying down wooden planks, boards, as the base, xps- a hard insulator- over that to further separate it from the ground and heating cable on top- the manufacturer states it can reach up to 40 c tops and finally the trees over that.

Not sure if sand would be needed in this case.

All that hooked up to a thermostat.

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If you are on the ground and trying to keep the roots at around freezing, then insulation is not needed. The ground temperature 0.5 - 2 meters down is a fairly constant 10-13C in all but the more extreme climates - both hot and cold. If you protect the surface from the extreme cold this will provide a source of heat from below. I keep my greenhouse at just above freezing and the ground in the center of the greenhouse is typically around 7C in the middle of the winter. I also have a fan that runs constantly to circulate the air which helps distribute the heat into the corners and keep it all from raising to the peak which is just over 2 meters. I would use the sand/grit around the pots if you use heat tape to 1) distribute the heat more evenly and 2) serve as thermal mass so the heater does not cycle on and off constantly (the probe for the thermostat should be in a pot).

6

This is great, thanks for sharing.

My thoughts behind the insulation below was that we dug 1m deep this summer for the waterline, so 80cm- ish feet deep the frost might go,down and I’d be losing a lot of heat in the wet soil, but since you mentioned that you’re greenhouse stays pretty much frost free at soil level all winter, that’s incuraging.

I do have some crushed rock laying around, basically gravel, though a bit larger in size then ideal,it should work when packed down a bit.

I’m looking to put some sort of fan in to keep the air moving a bit.

Thanks again

7

I think there is already some great information here.

I use a “ green shed “ in zone 4-5 depending on who you ask. A un insulated rough cut pine shed with a metal roof.

I run an intake fan, an exhaust fan, a circulation fan and a small heater set between 32-35 depending on outside conditions. I have seen 20 below for a few days, the shed drops to 25-28 when it is that cold. I also run a led light 8 hours a day. Not a grow light, just a led that was in the window or the correct color, light temp.

I think as mentioned above using the temperature of the earth is free heat, and it should be taken full advantage of. Many electronic devices are now wifi enabled so it allows you to monitor what is going on inside the shed/ greenhouse when at work or out, etc.

I have a cold frame/cold box which I have used for native trees, Japanese maples, and nana or garden juniper with only the juniper receiving winter damage or death. These trees freeze rock solid in the winter to the point of the ceramic pots exploding..

I also have wildly collected, pre bonsai and random stuff in plastic cement mixing trays with holes drilled in them on the North side of the house on the ground burned in maple :maple_leaf: leaves.

I have had one death in 3 years.

I have found that a nice quality meat probe is a great product to test temps in the ground or in the pots.

Fast easy and we all usually already have one kicking around.

If looking for wifi enabled equipment look to the “ grow industry “ if that is legal in your country.

This industry has many consumer grade products that are wifi enabled and allow tracking from the house, car, work, etc and many can be set up with low temp alarms. So when the alarm goes off, take the meat probe out and check soil temps inside the pots. Brings a peace of mind and then you can learn at what outside temps your setup crosses into the danger zone and adjust as needed.

Peace

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