Frost protection....tunnel in a tunnel!

[Duronal]

Hello all

I wanted to say a huge thankyou to everyone who has helped/encouraged me to keep growing over the last year, there is so many helpful people in this community it feels more like a group of friends then a gardening forum.

Today has FINALLY seen me finish off my poly tunnel i couldn't have done it without you,

Here's a pic for all those who have seen the steps along the way,




If i use a plastic green house in a poly tunnel am i going to get any increased frost protection? I would be hoping that the air in the mini green house would stay warmer than the normal tunnel air and thus insulate against frost. Any ideas?

Many Thanks

D

P.S your seeds are on the way Phreddy.

[ricwiley]

Thinking back to the frosty nights earlier in the year, I measured down to minus 7C and I do not think a mini greenhouse inside my greenhouse would have prevented frost getting to plants. I use an electric propagator on such nights or just bring the plants indoors.

Try it though and see how you get on.

Cheers

[Seahorse]

Last year I used small (unheated) propagators, inside plastic greenhouses, inside my 'proper' greenhouse. I would think it wouldn't have been enough on a very frosty night but temps certinaly stayed a couple of degrees or more above outdoor readings.

[Storming Norman]

I read a Bob Flowerdew book recently and he had a picture of his poly tunnel inside another poly tunnel. It looked a bit mad but apparently he grows pineapples in it and it is frost free. They were big tunnels though.

I wondered about the light levels.

[kentvegplot]

I hung some thick bubblewrap on the inside of a small section of the tunnel, and across half the roof (if you see what I mean!) which created a small area which I could then heat with a small paraffin heater. It worked very well.

[Two_Sheds]

I read a Bob Flowerdew book recently and he had a picture of his poly tunnel inside another poly tunnel. It looked a bit mad but apparently he grows pineapples in it and it is frost free.

Bob is over here in Norfolk though ... we don't get much in the way of frost.

[Sue]

Hi
I've got a coldframe and having run out of space at home took some tomato seedlings up to the allotment. Some I put in the greenhouse - now dead and some I put in covered propagators inside the coldframe and these have survived and looking very healthy. We've recently had two frosty nights and they survived as have some aubergine seedlings in their cosy nook.
So it does look as if covers within covers works?
Sue

[-pat m]

Hi – Your tunnel is fantastic great tension in the plastic congratulations!

This is a pic of my greenhouse in my tunnel – during the really cold times even with a eletric heater on the go the best I could do was keep the frost off –
You will get some extra protection in having two together (no wind on the inner tunnel) but you will need some form of back up for a cold snap – as soon as you get a little sun on the tunnel the main problem is keeping the green house (inner tunnel) cool!
Thanks for the pic’s

I’ve said it before ..your blog is great I may try it myself after reading yours!

Regards

Pat

[bramble]

Well done Duronal. Great poly tunnel and I am so envious. My toms are in my cold greenhouse, inside my propagator and covered over with fleece and polystyrene.
Nearly two weeks outdoors now and so far so good.

[Duronal]

do you think i could use a fleece cover (meant for the mini greenhouse) as frost proof staging.....

Bernard salt's book also lists using fish boxes as polystyrene cold frames when topped with plastic/perspex. I imagine bubble wrap would work.

[teakdesk]

My "greenhouse within a greenhouse"....

Wooden frames glazed with greenhouse glass and clipped together to form the "house". The closest half has 200 watt thermostatic air heater and 50 watt undersoil heating cables - the other half is unheated with a removable glass partition. There are a couple of old computer fans in there to mix the air around as well.

The tops lift for venting on hot days and as the plants grow and the season gets warmer the frames clip off to be stored in the garage leaving the greenhouse back as normal but with the undersoil heating if I want it.

Night-time temperature is easily held 15 degrees above the outside temperature even with only 250 watts of heating.

[-pat m]

My "greenhouse within a greenhouse"....

Wooden frames glazed with greenhouse glass and clipped together to form the "house". The closest half has 200 watt thermostatic air heater and 50 watt undersoil heating cables - the other half is unheated with a removable glass partition. There are a couple of old computer fans in there to mix the air around as well.

The tops lift for venting on hot days and as the plants grow and the season gets warmer the frames clip off to be stored in the garage leaving the greenhouse back as normal but with the undersoil heating if I want it.

Night-time temperature is easily held 15 degrees above the outside temperature even with only 250 watts of heating.

Great set up – I am interested by your use of fans – Could one use a domestic fan in a greenhouse in the summer to keep the air moving? Air flow will be a problem for me on still days this summer?

Regards
Pat

[SarzWix]

Pat, I use an ordinary domestic fan in my small greenhouse at home over the summer, it makes a big difference as this greenhouse doesn't have any ventilation apart from the door. I couldn't do it on the lottie though, as there's no electric

Duronal, nice tunnel It would certainly be worth a go with a mini-greenhouse inside the tunnel, or a sectioned off area with bubblewrap/polythene that you could put a small paraffin heater in?

[teakdesk]

Could one use a domestic fan in a greenhouse in the summer to keep the air moving? Air flow will be a problem for me on still days this summer?

Pat - the biggest problem with fans etc in the greenhouse is the danger of death from electric shock.

I built my current set-up as a safer method than my earlier attempts to heat or cool the whole greenhouse with domestic fan heaters (which can be set to blow cold!!). Even fan heaters designed for use in damp conditions carry some risk. You need to make sure the watering can or hose puts absolutely no water on the heater/fan.

You need to make sure you do not touch or move the equipment until the electricity is turned off outside the greenhouse because of condensation on the fan heater.

If you do decide to risk it first get a qualified electrician to install an outside weatherproof socket that is correctly fused and fitted with a RCD on the outside of your house not too far from the greenhouse.

All cables outside will need to be armoured cable or in conduit to prevent them being chopped with a spade. And remember that rats often chew cables so they could be damaged that way as well.

The greenhouse frame probably needs to be earthed as well.



Given the dangers I must urge caution.

If there is a chance that children will use the greenhouse I wouldn't put electricity in it.




PS the fans I use are 12 volt fans that came from a computer and are perfectly safe even if dripping wet !! But they will be too small for your greenhouse.