They will be fine with 40-50 now and then...I like to run mine about 64. This keeps them growing.

So, the answer is Yes. As long as they don't freeze.

Is it the textbook right way to do it? No. You should have adequate BTU's to maintain 64 with whatever mother nature throws your way.

45 is the usual recommendation for minimum allowed as long as it isn't for a long period of time. 50 would be better but I know the problems you face myself and I can live with 45. Any lower than that and I start covering them.

One thing that does help IF you have the room is to tent over the plants with a second layer of plastic (not touching) - a tent inside the greenhouse - and stick a couple of incandescent lights inside the tent. Good for an additional 20 degrees or so on the really cold nites.

Dave

I'll let you know tomorrow... Temps outside epected could be between 19-24F. I have no heat or power in my GH (22' x 50') I've covered my flats with an extra sheet of plastic after placing them on the ground. I am hoping the ground will release heat to the plastic. I am thinking that if i kept them on the benches there wouldn't be any residual heat to help them. It was sunny today so i kept it shut hoping that would help the soil temps to hold a bit more heat. got quite warm in there! Maybe a bit too warm...

I also have a 1500 gallon open water tank that i use for some fish and i floated some styrofoam on top and set as many flats of marigolds in there as i could. Covered the tank with styrofoam. The last time the temps dropped to the high teens i lost about 80% of my marigold seedlings.

Hope i can sleep tonight!

Poppa

About May 1 I get tired of dragging all my plants in and out of the garage every day, so move them down to the greenhouse. For the next 30 days, I feel fortunate to keep the temp above 40 every night. My tomato plants suffer no ill effects.

Mytime, snowmobile trailer, roll em in and out... just a thought.

The tomatoes should survive 32F. I use 600 litres of water to moderate tempertures in my unheated greenhouse and the only effect is to prevent below 32F temps. Ironically, the only tomatoes I have lost were sub-arctic-plentys. They aren't happy but they live. They do better if they are bigger. I'm starting mine indoors and putting them in the greenhouse at the first potting up. Using the dense planting approach I have 64 varieties planted and ~150 growing plants in two trays. The two trays could handle 300 plants; but I only have room for 50 in the garden. :)

I'm going to cheat and supplement with an electric heater.

So the overnight temps reached 23F last night. No damage to any of my tomatoes (big boy, celebrity, Super sweet 100's). Actually no damage to any plants in my unheated GH. I left some trays of marigilds out and they all were fine. Whew!

I did have some asparagus spears coming up in the garden which froze.

Thanks for the posts guys. Poppa glad to hear your stuff survived. I am in Rhode Island not far from you and timmy. Had the same frost last night and ran a 1500 watt heater all night and tested temps throughout. It kept the temp 10 degrees warmer when it was 35 out but once the temp dipped to 28 it just couldn't sustain the temp more than 3 degrees at 31.

So poppa would you assume that it appears that plants like tomatoes suffer wind chill similarly to human beings? It seems like a plant that is not stuck in cold plus wind can survive just the cold if protected.

Jon, the snowmobile (or as we call them up here...snowmachine) trailer is a great idea, except that ours is too large for the garage. I do use garden carts, the grandkids wagon, and shelving on wheels, but even that reaches a point where it's just too much as the plants get potted up in size.

soulreaver: While i don't have heat or power i do have a few things that work in my favor.

First off, my gh is pretty good size, 22 x 50 inside. The size helps to moderate temps.

Second, i have a good size tank in there, 1500 gallons, and that has also helped to moderate temps. Prior to installing the tank (Thirdly, i have built a greenhouse within a greenhouse. I have 2 foot dead air space on all sides and 3 feet in the roof. My goal was to build a "Solaroof" design where the dead air space is filled with soap bubbles at night to act as insulation. I have not really needed it as i grow (not just harvest) a number of cool weather crops in there all winter long. Tomatoes and potatoes need a couple of more degrees and if i decide i want to grow them i will need to add the insulation. As it is my tomatoes will bear fruit until December when temps fall below freezing. I start my tomatoes in march and have only a few scares. It does get quite damp and i would likely have molding issue with tomatoes anyway. It literallyr rains inside when the temps drop outside.

Last year I actually had a citurs tree survive all winter in there, though it did die back to the roots. Again, if i wanted oranges in winter i may need to add the foam insulation, but i'd have to run power out there and i have no plans to do so quite yet.

Poppa

Poppa I only have 1 lay of insulation and it is a 500 dollar greenhouse plastic 6 mil. But my temps are definitely 5-7 degrees higher than your temps on most nights and I have a red brick foundation on the greenhouse which absorbs quite a bit of heat during the day so I hope those two things combined with the fact that I will have 2 1500 watt heaters running on the colder nights would be enough to keep my greenhouse above 45 from this point on.

I am also wondering if once I have 150 flats in the greenhouse all watered during the heat of the day if the soilless potting mix of peat and vermiculite soaked with water in in the 150 flats will contribute to thermal warming during the nite.

Also I have 6 105 watt heating mats which will be used for seed germination and those will be running during the night as well. All these little heat sources, the mats, the 2 1500 watt heaters, the brick foundation, the 150 flats you think this will be enough to combat a 25 degree night here and there? I know there are alot of variables that I am putting fourth but like you just posted I have all these little things that might make a difference going on in my greenhouse too.

If your greenhouse is 22x50', I would just get a thermostatically controlled kerosene bullet heater in there for the cold nights.

I have a 7x10' x7' tall greenhouse that is built against the house, I live South of Boston MA
I actually dug down into the ground, so the front is only 5' out of the ground
It faces South, no heat....it has a "cement" foundation maybe 12" deep
I also have a 55g drum of water that stays in the GH to help moderate temps
I dug down inside maybe 2' & put some rigid foam around the outside perimeter
Usually the end of Feb is the last time it dips below freezing
I put 3 TM plants in as a test, I wanted to see what would happen
March 16th Temp dipped to 31.1, 2 of the 3 died
March 22nd Temp dipped to 31.6, 3rd plant still alive
I'm past the last freeze now & just moved 60 plants from my sm indoor greenhouse to the outside greenhouse
I bury the 3-4" pots in the soil...Daytime temps go up to 55-65
Today it hit 74 with a nice sunny warm day

Tomatoes can survive temperatures 34F and higher. I have had tomatoes planted that stayed at 38F low without protection.

Remember that when they say low will be, eg, 38F it is not going to be all night long. Most Often the forecasted low will last no more than 2 hours. If the day before the high was 55F and the following day will be also 55F, then the lowest between those highs will last just couple of hours. BUT when they issue a frost warning, that is different. In that case a cold freezing front will be moving in with high winds that will cool off the air and ground much faster and will last longer too.

Well, the thing to remember also, they might survive but you are not doing your tomatoes any favors if they are sitting in cold trays. There has to be some middle ground to provide not only survival but growth and minimizing stress of dropping to low temps is something to remember. I have a hoophouse, large tarp like plastic dome, it is a bit of a game. If I only have occasional dip into nights low I can get away with wrapping electrical blankets over shelves for the night. If I have days and nights on low side for prolonged times there is no reason to stress seedlings so much.

Timmy, which heating system would you recommend for my upcoming 50x110 8 foot side walls 11 foot roof height 6mil single poly hydroponic greenhouse. Temps in my area falls to 32f at night and 60f in the day for two months. And would it be cheaper to use wood, kerosene or LPG.

Some of my tunnel grown tomato plants got frost damage on Monday. Interesting aspect is that damage only extended about 1/4th the distance from the end and I have Windows open on the opposite end of the damage. Cold air acts in mysterious ways. Outside temps had dropped to 30*F for the morning and I had no heat or fans in this structure. In ready to call it a season for these plants but I may stoke wood stoves for 2 other structures where I have 496 tomato and 474 pepper plants still going strong since early spring.

Thanks barrie for the advice. I'm more interested in wood heater bcz wood is cheaper in my area and i don't have to get connection for natural gas and don't want to deal with kerosene at all. I will be using circulation fans all night during winter. But the question is can the tomato plants survive the outside 32f temp when circulations fans are turned on all night even without heating turned on? In my area 29f is the lowest during last 50 years, most of the time it stays above 32f. I'm asking this bcz i don't want lose my sleep bcz of worrying about heating system not working properly.

The short answer to your question is probably. Different researchers have shown that well established plants can tolerate temperatures below 30*F but delicate new growth may be damaged. The other problem is that wood heat is reliably unreliable. Even last night I loaded larger unsplit logs into my stoves and the heat differential was a mere 6*F.

Also keep in mind that some other research studies have shown that under certain circumstances the inside temp may actually dip below the outside temp for a period of time.

Just use extreme care when flirting witth low temperatures.

Hmmm. That's worrisome. What type of heating system would you recommend then? I obviously don't want to lose plants bcz its not a small investment for me.

I agree that wood is cheap and there is no reason why you could not figure it into your plans. I would only recommend a backup heat source that you could readily revert to if the wood was inadequate.

I still don't know where you are but if 29*F is your lowest temp you may not want to even mess with wood. Starting fires in rainy low pressure conditions is not that easy. You may get irritated with smoke in your greenhouse due to inadequate flue draw.

Many specialists even condemn wood stoves for structures. They usually require a lot of interrupted sleep to tend to fires during the night. An alternative to an indoor stove in your situation may even be an external boiler unit with an internal heat exchanger.

If you're wanting to use wood for heat, consider a "rocket stove space/mass heater" setup. Combining a rocket stove heater with a large thermal mass/heat storage could work very well in a green house. The thermal mass/heat storage could be a masonry or concrete block wall down the center of the greenhouse, with the exhaust gases from the rocket stove routed through the thermal mass to extract as much heat as possible from the exhaust. Fire the rocket stove for an hour or so to heat things up, and let the thermal mass/storage release heat into the greenhouse overnight.

That use deviates from my purpose of a wood stove. The reason I add wood every few hours during the night is to extract every BTU that I can to keep plants warm. Often I push the limits on my 160,000 BTU/hr. stoves in my larger structures. The sides of the stove is glowing red in order to maintain an inside temp of 20*F above outside temp in my 30x96' structure. I have up on heat sinks many years ago because they usually leave you hanging after 2 a.m. when you need the heat the most.

Well, if you're pushing smoke and hot air up the chimney, you're not "extracting every BTU that you can." Even without a thermal mass/storage, a rocket stove design will generate more heat with less wood than a conventional fireplace or conventional firebox with chimney.

A more modern stove design with secondary air injection will perform better than a plain firebox design. Sourcing the combustion air from outside the heated space helps as well.

In theory one you want to be as efficient as possible but in practice we are talking about a film covered framework that tends to leak BTUs like a sieve. I use a Riteway and a Hitzer stove that were both considered efficient 40 years ago. A fireplace or Franklin type stove is no comparison to these wood stoves. But although I may burn a chord of wood in a week between those two stoves the cost is still a fraction of what the other heat sources run to heat the same space.

Heat sinks (thermal mass storage) is not only a waste of money but a bigger waste of valuable space.