seeds How low of temps can seedlings handle in an unheated mini green house?

filmost

filmost

I have been hardening off half of my seedlings for about a week now, and am considering leaving them outside in a mini green house tent type thing. It will be unheated.
 
Currently my weather forecast for the next several days shows night time lows of 3C/37F and daytime highs between 13C/55F and 16C/60F---Next week the temps are forecast at 6C/42F ~ 11C/51F at night and 16C/60F ~ 20C/68F during the day.
 
Would the seedlings be able to handle 3C nights since they'd be protected from wind? My home is not centrally climate controlled and my grow area fluctuated between 5C nights and 20C days throughout the winter.
 
I think they will be okay but need a second opinion.
 
3C seems a bit low but I guess you'll find out - I also have some seedlings I cant physically fit in the house and we're forecast 1C at the end of this week. I guess this is going to be interesting! 
 
One thing I have noted is that the ones I have in the greenhouse (5C min at night) are growing a lot slower than the ones inside (15C at night)
 
moosery said:
3C seems a bit low but I guess you'll find out - I also have some seedlings I cant physically fit in the house and we're forecast 1C at the end of this week. I guess this is going to be interesting! 
 
One thing I have noted is that the ones I have in the greenhouse (5C min at night) are growing a lot slower than the ones inside (15C at night)
Click to expand...
 
Yeah I definitely expect slow growth, but I have been having slow growth all winter (expected) so it isn't too big a deal. I just don't want them to die, lol.
 
3C is definitely on the low end, but fortunately its only for a couple of days, and the forecast might change as well. I guess I will try it with a few plants first then put the rest out.
 
depends on how much the greenhouse insulates them from the cold. Peppers will live as long as the roots aren't frozen solid, they can handle a light freeze(although expect some death /  pruning ). So 3C should be fine,  especially since it's warming up during the day. You can store thermal energy in rocks, or water and set them next to your plants to keep them a lil warmer.
 
I got a small forced air heater that can heat my small shed so i won't have to worry about it, also plants will grow much faster when they are toasty warm.
0004601376286_500X500.jpg
 
I do this every year with my peppers, though I always put the black plastic mulch down first (to warm the soil), plant the seedlings in holes punched in the mulch and build a low row cover over top. The plastic mulch warms the soil making a warmer microclimate during the day, and radiating heat after the sun goes down. The low row cover traps that heat and holds it down next to the plants. You can see my method and results in my last two glogs. I'd post pics but am waiting for a new computer since I fried the last one, and am forced to use a 20+ year-old Emac until then. 3 degrees celsius should be fine as far as the plants surviving if you have them out of the wind... they won't grow much, but that's OK this early in the season.
 
Try building the green house and put a thermometer in it to see how the temps fluctuate (I'm thinking a chep type with "out" probe, that can also recall min/max).
 
If you get min. temps of under 10, I don't think you should bother. The plants will not grow (or grow really, really slow). 
 
On the other hand, if you don't have space for them indoors anymore, you could move them. They shouldn't die at those temps...
 
Mine are outside It is 40s in the morning 70s in the day. They dont grow much, but its more light than I could give them in my house
 
I have an answer for you - my seedlings (very young) went down to 3C last night and about half of them were fallen over this morning. It was only 3C for a couple hours too.
 
So the answer from me is: 5C good, 3C bad.
 
How big are your seedlings? I would suspect the smaller the riskier. I would monitor the greenhouse thing vs outside temps a day or two to see the difference it made. I'd also worry that a forecast of 3c could easily drop to 0c for a few hours. But that's just me and my girlfriend is always calling me a nay-sayer. :rolleyes:
 
Hope they fare well!
 
Thanks for all the response! I ended up deciding to wait til it warms up a bit more before leaving them out; I mean hell, I'M cold.
 
Correction, or update! As of 3pm, they've all recovered. Marvellous. Robust little things aren't they?
 
 
AaronRiot said:
How big are your seedlings? I would suspect the smaller the riskier. I would monitor the greenhouse thing vs outside temps a day or two to see the difference it made. I'd also worry that a forecast of 3c could easily drop to 0c for a few hours. But that's just me and my girlfriend is always calling me a nay-sayer. :rolleyes:
 
Hope they fare well!
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very small - as in, not even first set of proper leaves. I literally can't fit them anywhere but the greenhouse, every windowsill is full of plants, so I had to chance it against my better judgement. I did expect them to die to be fair, which they haven't...always full of surprises! 
 
Pic - as you can see, all look fine now! 
 
http://imgur.com/x8w9UqF
 
[I know, some are sort of tomatoes and not peppers!]
 
 
 
An older plant was also out there, it seems far less bothered....
 
http://imgur.com/8EEUsJC
(the leaf damage is a separate issue...we don't talk about that...lol)
 
Well I'll be damned! Still, I think I will keep bringing them in until monday when temps pick up a bit. I need to move my portable green house outside as well, just in case the wind picks up. We have had several extremely windy days over the past couple of weeks.
 
This is starting to get interesting now. I've been graphing the temps on a "rolling chart" overnight - long story. Last night the low on that graph is 1.8C, the chart currently plots "backwards" i.e. it's 12C now, and was 1.8c a thousand readings ago, readings are sent every 8 seconds so that's 2.5 hours ish for the whole graph - a work in progress, need to enhance the graph somewhat :) 
 
Anyway the point, 1.8C for some time - plants not even bothered. 
 
http://imgur.com/8hBV6tk
 
We have a few "close to freezing" nights coming up according to the forecast, so might be able to get some really good data. It's certainly beginning look as if you can harden chilli and tomato seedlings off to handle some surprisingly low temperatures, never mind the plants.
 
Wind - well, that's another story. All this data is coming from an unheated greenhouse. I suspect the wind "chill" would yield a far more devastating blow to the plants...
 
moosery said:
Wind - well, that's another story. All this data is coming from an unheated greenhouse. I suspect the wind "chill" would yield a far more devastating blow to the plants...
Click to expand...
 
Exactly! Wind is definitely your enemy... it's not just the cold, but the dryness of it that sucks the life out of your seedlings. Most of them have a large surface area for their size and the stems are very tender, leaving them open to getting battered as well. The plants need to stiffen up and be hardened off before you put them out in the wind.
 
 
Exactly! Wind is definitely your enemy... it's not just the cold, but the dryness of it that sucks the life out of your seedlings. Most of them have a large surface area for their size and the stems are very tender, leaving them open to getting battered as well. The plants need to stiffen up and be hardened off before you put them out in the wind.


How long do you usually take to harden your plants off? The ones that I have been working with will have finished 10 days worth as of this Monday. Still have another set I need to get started on too.

The weather still won't be consistently above 50F for another week of so though, so I am still taking them in a night.
 
filmost said:
How long do you usually take to harden your plants off? The ones that I have been working with will have finished 10 days worth as of this Monday. Still have another set I need to get started on too.

The weather still won't be consistently above 50F for another week of so though, so I am still taking them in a night.
Click to expand...
 
I take my cues from the weather. If we're getting stiff wind I leave whatever I have covering my low row cover on the frame. Early in the season I use 4mil sheet poly since it does a better job of keeping in the warmth. If it warms up enough for the plants to be comfortable at night but the winds are still too strong, I use a spun-bonded agricultural fabric like Agribon-19. The Agribon has the added advantage that it lets the rain through instead of letting it run off.
http://www.johnnyseeds.com/p-5452-agribon-ag-19-floating-row-cover-83-x-50.aspx
Eventually, the winds die down as the season warms up, and I remove the cover and frame and turn the plants loose to grow solo. We can still have freak wind squalls anytime, so I always stake up the plants when they get more than about 30cm tall.
 
Here's a couple of pics from last year.
SANY0698_zpsc03c065e.jpg

SANY0699_zps26b5cc3d.jpg
 
Impressive data moosery! Definitely puts things into better perspective. Is your greenhouse the completely sealed kind?
 
filmost said:
Impressive data moosery! Definitely puts things into better perspective. Is your greenhouse the completely sealed kind?
Click to expand...
 
 
It's a tiny 6x4ft cheap perspex/aluminum thing, so it's sealed as in all doors/windows close and no wind inside but its not sealed as in airtight, not by a long way.
 
 
 
It's a tiny 6x4ft cheap perspex/aluminum thing, so it's sealed as in all doors/windows close and no wind inside but its not sealed as in airtight, not by a long way.


Ah k. Same as my little portable one then. Cool, I am planning to take mine it and leave plants in it over night starting this week.
 
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