Insulating a Coldframe - advice please

[Ron]

I have a 4' x 3' coldframe which isn't assembled yet. If I insulate it with a layer of thick bubble wrap, do you think half hardy plants (ok down to 0C) grown from seed would survive in it? I'm aiming to plant at the beginning of February.

[Barbara]

Mine is made of bricks, hubby built it for me, it has a plastic lid and I line it with bubble wrap, I stand the plant pots on half a wooden palette, I hope this helps Ron,

[Ron]

Thank you, Barbara, I like the pallete idea.

[Barbara]

I think Ron, if it ever gets well below freezing I may put a tea light in there.

[Ron]

Another good idea, Barbara, I'd been wondering how I might heat it if needed, never thought of that.

[Ron]

Thanks, Barbara, for your input. Your mentioning the tea light set me on a different track. I'd been searching online for info regarding insulation with bubble wrap without getting a lot of useful results. When I searched from the point of view of a heated cold frame (or greenhouse), I found what I was looking for. Bubble wrap is great for cutting down heat loss, especially when used with an air gap, but is next to useless for insulation against frost where there is no heat source. I think I will grow the seedlings indoors, I think its too risky in the cold frame.

[Chuckles]

Ron,Barbara, dug up these 2 bits of info from way back that you might find useful

Nov 1, 2006 20:49:32 GMT Chuckles said:

You used to be able to get thin polystyrene on a roll for putting on room walls for extra insulation, not sure if you can still get it at DIY stores. You could line your cold frame out with that, it would cover any gaps and give you a little more protection too. Also ceiling tiles in poly too. I use some of the polystyrene trays that hold the small 3" pots for cuttings in pots over winter, you could uses those as a base.

Sept 17, 2008 22:26:26 GMT Missredhead said:

someone told me that you can put a lit tealight on a saucer with a little water on it and place a terracotta pot upside down over it and place it at the bottom of the GH it keeps the frost out.
Haven't tried it myself though as the bubblewrap kept the frosts at bay last year.

[Ron]

Sounds interesting, Chuckles, thank you. Polystyrene sounds worth looking into, and Missredhead 's used a tealight too, which Barbara mentioned. I should think B & Q or Homebase might have the polystyrene.

[Tig]

I bought a roll of the foil lined insulation like this Ron www.screwfix.com/p/thermawrap-loft-insulation-0-4-x-5m/76477?kpid=76477&cm_mmc=Google-_-Product%20Listing%20Ads-_-Sales%20Tracking-_-sales%20tracking%20url&cm_mmc=Google-_-Shopping%20-%20Building-_-Shopping%20-%20Building&gclid=CPT3-OnUhskCFWsTwwodicIMWg

Not only does it insulate a bit it also reflects light which helps stop the seedlings getting straggly. I keep the polystyrene trays that multipacks of pansies and the like come in and pack the bottom of the coldframe with those, then put a layer of the thermo wrap over the top and up the back wall of the coldframe.

Beware using the tea light if the area of the coldframe is not very big, they can use up the oxygen and cause condensation which can cause seedlings to damp off and encourage mould on tender plants. Also, only use with glass / aluminium frames.

It also depends what seedlings you are hoping to grow in it. Some can cope with cooler temps than others.

[Ron]

Nov 10, 2015 20:23:06 GMT Tig said:

It also depends what seedlings you are hoping to grow in it

Bidens, Felicia and Lobelia.

[Tig]

They are all spring sown and I would probably start them indoors March/April time, you should be able to harden them off in your cold frame in May if we aren't having major frosts.

[Chuckles]

Ron,Barbara,Chuckles,Tig,

That foil lined insulation looks great stuff Tig especially as its only 4mm thick compared to 55mm of Polystyrene

[Ron]

Nov 11, 2015 13:46:29 GMT Tig said:

They are all spring sown and I would probably start them indoors March/April time, you should be able to harden them off in your cold frame in May if we aren't having major frosts.

I'm also sowing Anagalis, Diasca, Nemophila and Sanvitalia which I think are hardy. They're all for hanging baskets. I wanted to sow them early to get the baskets off to an early start, so I need them all at the same time. I have read that Feb 1st is the usual time for an early sowing under glass.

[Ron]

Tig, Chuckles, the foil insulation is similar to something I've already looked at and it's unfortunately not effective in my situation. The surface of it is excellent for reflecting radiated heat so if you have a heater it will work well. In an unheated cold frame (or greenhouse) it would be detrimental as it will conduct heat more easily. It is loss of heat through conduction that is the problem. I've looked into polystyrene, bubble wrap, creating air gaps, they are all effective but it obviously depends on the temperature. If we get severe frosts the plants would be at risk and the frame is too small for a heater.

I'm sorry not to take any of the advice I asked for (I know that can be annoying!) but I think it will be safer to grow them indoors. I'll still set up the cold frame just to have somewhere to keep them and avoid mess, then use it to harden them off by taking it outside later. Thanks, anyway, for your ideas.

[Chuckles]

Don't be sorry Ron, asking for advice and sharing ideas is how we all learn

[coppice]

Now this mostly based on trials in NH-VT-NY.

Soil just plain old dirt in the bottom of a trench tends to run about 42F / 6C. If your trench is covered over by glass or other 'shelter', that protected space cannot get warmer than the ambient temperature of the soil after the sun goes down.

I built my last cold frame in Henniker NH and covered the glazing with clear plastic. Inside I ran a kerosene lantern after sundown. It kept the interior above 50F / 10C on nights that got as cold as -25F / -34C. On a 4 foot by 16 foot coldframe.

Burning K-1 (kerosene) is stinky, ultra refined parafin is much less so. I also used a minimum-maximum thermometer in it to check.

[Ron]

Thanks, coppice , for your input. Only just noticed it, sorry. My cold frame is only 6' x 4' and using a heater that gives off fumes would adversely affect the plants unless I ventilated it and that would defeat the object. 

[coppice]

Ron, drop-light with a 100 watt filament bulb should do for your smaller cold frame. A string of filament Christmas lights will also do the trick. Ron,

[Ron]

coppice, thanks, but there is no power supply. I live in a rented flat so I couldn't put one in. Thought of batteries but not really feasible.

[Dutchy]

Have you found the trick of an upturned terracotta flowerpot on top of another normal standing one with a hm waxine light that burns for 6 hours.
They say it works.
growingarden.wordpress.com/tag/greenhouse-heaters/

My uncle uses what we call a peut
He puts a sheet of metal on top and burns things real slow. No bad fumes according to him and it keeps things above freezing.