insulating polytunnel?

[SelkirkAlex]

I have seen various ideas to thermally insulate polytunnels, the most popular seems to involve lining the inner surfaces with bubble wrap.

is there any real point / advantage to this?

my tunnel has an electric greenhouse heater that comes on at 2C, so last winter my tunnel hovered just above zero at night. I had pretty much accepted that for where I live.

active heating is jut too expensive and pointless given the lack of sun.

does passive insulation offer any benefits better than what I already have?

[Small pumpkin]

Tricky one that. Personally I've never tried. I can't work out a good balance between insulating and light. If you insulate for warmth you're probably going to block out a considerable amount of light which due to our location is at that time of year very limited anyway.
I find the best thing is not do any gardening in winter . I'm probably not living in the best location to be a fair weather gardener.

[SelkirkAlex]

is there such a thing as fair weather in scotland?

[chris_m]

is there such a thing as fair weather in scotland?

Yes, it's when the rain is just coming straight down instead of sideways

[roitelet]

I've tried to insulate with bubble wrap and the main problem is fixing it in the tunnel. Tried all sorts but whatever I tried was a pain. This year I am considering constructing a tunnel within the tunnel. I'm thinking along the lines of uprights with flexible pipe on the top to give a roof covered with either bubble wrap or thick fleece. That way I will be able to create an airspace between the inner and outer layer. I have a gas heater which will only heat the inner tunnel. I only use the heater from about the end of Feb until May or when it warms up enough.

My tunnel is 3 x 6 mètres and I envisage the inner tunnel to be about 1 x 4 mètres that way I will be able to access all round the inside one.

[SelkirkAlex]

what will the effects be? are there any practical benefits in growing?

[DannyK]

This might be interesting. I remembered he's spoken about double tunnels on GQT.
Double polytunnels; grow tropical fruit & veg.. at home | Bob Flowerdew

[bramble]

Its not just about keeping your tunnel heated. Its about the light levels.
Without sunlight and brightness nothing will thrive no matter how high the temp is.

[SelkirkAlex]

that's exactly what I was concerned about bramble, a possible couple of degrees increase that wouldn't serve any usable advantage.

sounds exactly like my efforts in my first winter growing here, desperate to get heat before I learnt of all the other problems in winter growing in scotland.

[bramble]

I know how you feel Alex.
I only use my greenhouse for overwintering my gersniums and fuschias.
I do however start my sweetpea seeds in the greenhouse in late stumn and overwinter them there to give an early start in the spring.

[MarkPelican]

A couple of years ago, I insulated the polytunnel with bubblewrap, built a tunnel within the tunnel (with the left over bubble wrap and put a heater inside that to trip in at about 5C.

I got lettuce throughout the winter in the majority of the tunnel and got my tomatoes to germinate early.

Last year I didn't do anything special, got lettuces throughout the winter and germinated my tomatoes in the house.

So I don't know.

[bramble]

Agree Mark.
I dont actually like to eat lettuce in the winter, when its cold.
I germinate my tomato and pepper seeds indoors in my heated propagator.
For me, it would be a waste of time and energy.
Having said that, I cant wait to get started every year, so perhaps that break is good.

[ESBkevin]

There is a US gardener called Patrick Dolan (and his cat Oscar) that does Double hoop house growing to extend the season and he has a poly tunnel with some further glazed units inside.
He appears to be successful at producing vegitables all year round even though they have snow cover extensivly in his area.

Extending Your Growing Season in Winter: Can Your Garden Survive the Cold? | Ready Nutrition

search yootoob for oneyardrevolution to see his construction meathods and results.

For my part I attached bubblewrap inside my greenhouse last winter, it was a faff and I'm not sure it helped really. I shan't repeat the exercise. I usually have a 4 shelf blowaway inside the greenhouse as the plastic cover gives an extra level of insulation against the cold. I've tried a parafin heater, candle/tea lights and plant pots etc. and a huriccane lamp to give overnight tempreture boosts. To be honest early seeds do best just in the house or in the shed with and electric propogator.

HTH.

[SelkirkAlex]

interesting reading but to quote him " Cold frames may still be useful in Zone 7, but may have minimum usefulness in Zones 8 and higher, "

most of the uk is zone 8 with parts of the penines and of scotland being zone 7, all tends to suggest going to great great efforts will have little benefit, maybe we should just stick to cold weather crops in the uk

[veggiechicken]

In Ye Olde Dayes I use to bubblewrap the GH, put tube heaters in on timers, paraffin heaters etc and for what? To keep a few geraniums alive over winter.
Now, I save myself the hassle and expense and garden with the seasons. I can still keep the geraniums alive without all the faff, winter veggies grow in the GH without heat and benefit from that bit of protection from the weather - as do I when I pick them.
I know you're further North than I am, but I still wouldn't do anything special to outwit winter. Try a variety of veg and see what grows best.