[Esthalon]

Hi, We've just got our first polytunnel up and running and all is going well.

What I'm wondering is is how cold is it likely to get in the winter. i.e. At night if it's -5C outside what temp am I likely to get inside the tunnel?

Also if I built a big fleece cloche inside the tunnel, what if anything would that do for the min temperature?

The tunnel is 14 x 25 ft, single sheet polythene. I'm based in Rush North Co Dublin about a 1km inland.

Reason I ask is that in addition to wanting to grow veg I also want to use the tunnel to overwinter my pelagoniums and a huge Yucca I have that has suffered really badly the past 2 winters. I've also bought a Boungainvillea and a lemon tree, I'm wondering weather to plant them in the ground in the tunnel or to put them in pots so I can bring them indoors if the tunnel gets too cold.

Any advise on worst case scenario winter night time temperatures & what to do to mitigate them would be much appreciated.

June

[michael brenock]

The temperature in a tunnel can drop lower than the external temperature at times especially towards the early morning. Putting fleece inside would certainly help even with a lift of one or two degrees. What you really need within the tunnel is a source of heat eg electric heater with or without fan. If you burn anything within the tunnel you must ventilate it as carbon monoxide and dioxide are released on combustion. A long sloping chimney coming from a simple burner is often used. The fuel is usually a peat briquette or turf or slow burning wood. The stove can be made from something as simple as a tin can with a narrow pipe (2-3 inches diam). A look in the internet should yield a few more ideas. Finally the tunnel protection on it's own will not give protection from severe frost, the plants within the tunnel are more susceptible to frost damage having been grown for some time in the tunnel.
michael brenock horticultural advisor (retired)

[heno55]

you could also put a filled water butt or a few 5gallon drums of water inside when frost is forecast these will act as a heatsink and keep temperatures up slightly especially if they are dark in colour and have been exposed to sunshine during the day this is what i am doing, i also have recently purchased a lemon tree and when the forecast is for 5deg or less then i wrap the tree in a few layers of fleece.

[Esthalon]

I just wanted to say thanks to all for your insight and advice. I will now prepare for the worst!

I plan to get an electric greenhouse heater that will kick in if it goes below 5C, I can get one online for €29.99.

Also going to use frame of old dome tent with bubble wrap to create a "tunnel" (dome) in the tunnel. And I may use fleece too for good measure!

Thanks again all for your advice.