Heating a Polytunnel

[Greenmax]

Hi This might seem like a silly question (I am a polytunnel newbie) but can you heat a small polytunnel? Mine is 2 x 2.5m

Advice please????

[boboff]

I am sure you can, but not sure why?

what are you trying to do? Could you not more sensibly use your house with its own heat?

[oldjerry]

Agreed ,think about making a propagating bench,using electric cable ,inside your tunnel then plant out in the tunnel.Let us all know if you need more detail. Best Wishes.

[Greenmax]

Hi Thanks for the advice. I suppose I was thinking it would not be warm enough to grown seeds in polytunnel at the moment. I already have seeds starting off all over the house and will soon run out of room.
The propagating bench idea sounds really good and I would love more details please

[oldjerry]

Have alook at www.freeplants.com/bottomheat.htm (advance apols if it don;t work ,I'm crap at links) nb the photo in this link shows the cable before it's covered with a layer of sand. I'd stick the whole lot on a table or something.
Best wishes.

[okra]

Have alook at http://www.freeplants.com/bottomheat.htm (advance apols if it don;t work ,I'm crap at links) nb the photo in this link shows the cable before it's covered with a layer of sand. I'd stick the whole lot on a table or something.
Best wishes.

Good advice and the link works perfectly - very interesting article

[Cassiepod]

It probably is warm enough to start stuff in the polytunnel now. I planted some seeds in the ground very keenly at the end of January and when I popped in on them today a lot of them have germinated radish, mizuna, lettuce and something else. That's in deepest darkest Aberdeenshire with some very frosty nights. I wouldn't put anything tender out there yet but clearly more robust stuff is starting to think about growing. I have all the tender stuff starting out in the house, I'm keen to get a head start this year, a lot of stuff didn't have long enough to get to full ripeness last year.

[Greenmax]

Thanks everyone for your help

[MuddyWitch]

I treated myself to a few of those 'mini greenhouses' from £streacher a few years ago. I find if I pop seed trays in those & zip them up, (within the main tunnel) I can acheive a god germination rate a good two to three weeks earlier than normal.

MW

[sarahturner]

Hi,
I have insulated my polytunnel and heat it using a small propane heater. I used greenhouse bubble wrap to line the inside of the tunnel which lets a surprising amount of light through but keeps the heat in and then have installed a small thermostat controlled propane heater. This is enough just to keep the temp at between 8 and 10 deg C at night for early tomatoes etc. I got the bubblewrap from LBS warehouse and stuck it to the tube frame with sticky velcro strips so I can remove them without damaging the tunnel and the heater from First polytunnels.

Hope this helps

Sarah

[wulf]

I was getting plenty of stuff started in the polytunnel in February. It rarely got down to freezing inside and was often pleasantly warm on sunny days. You can also use further insulation inside - even just putting a plastic cover over a seed tray will give an extra layer of insulation while still letting the light through.

In fact, for the past month or more, the problem has been keeping it cool enough (various mesh screens have been added so we can leave the doors open and still it goes above the maximum 50C level on my Min-Max thermometer on the sunniest days).

Wulf

[SaveSomeGreen]

I would have to agree with wulf, , biggest concerns will be keeping the bugger cool enough when the temp gets up. The victorians used to use fresh manure underneath the soil as the rotting of the doings toasted it up a treat.... make make things a little whiffy though!!

[EarthTongue]

Hi Greenmax,

some ideas for you -- but you might not have space for these in your polytunnel as it sounds pretty small.

1) Keep some rabbits (or guinea pigs) in there, in a suitable enclosure, under the potting bench.

Livestock can process some used greens for you and add a little heat & CO2 to the polytunnel. Move them out when the weather warms up.


2) Add some thermal mass to collect heat and regulate the temperature swings.

This could be done in various ways, either having a dark coloured water-butt inside the tunnel (or a 55 gallon drum etc) or by adding some rocks/bricks/broken paving slabs etc. Going down the water route, you could keep a few fish in there and grow duck-weed for the compost heap too.


3) Add a compost heap.

Heat, CO2 and compost in the tunnel. Alternatively, do your composting outside along the most sun-less edge of the tunnel itself. This might, at least, buffer that side against the external temperatures, even if the compost doesn't heat up too much.


4) One or two of those reflective car windscreen sun-shields (the aluminium foil on bubble-wrap ones) could be tapped along the northern wall to reflect more sun onto the internal beds and insulate it a little (as has already been suggested.)

HTH.

[oldjerry]

That strikes me as innivotive and really interesting,hats off to you.Especially the livestock under the bench.
BW.

[EarthTongue]

Hello oldjerry,

actually, hats off to Anna Edey of Solviva fame, as using livestock as greenhouse heating elements is something she writes about (along with many other interesting topics.) There are also some folks over at the permies.com forum doing some interesting stuff (in the US) using rocket mass heaters to heat grow beds in greenhouses.