I am not convinced by arguments that heated greenhouses and polytunnels are a viable sustainable option. I think that, for the most part, we ought to be putting more energy into growing foods suitable for our climate. That said, there will always be some things on a household scale (like tomatoes and peppers) that need a little extra heat and that we don’t want to do without.
This year, I have been able to germinate heat-loving seeds without investing in a heat mat and propagator by putting them on top of our oil fired boiler. But we will be moving away from that and I am not sure that we will have such a good spot for germinating seeds once we move towards using wood burning/ multi-fuel stoves. I am not sure what the solution will be then but it is a problem to be considered in the future.
Growing indoors (in an area that is already heated for our benefit anyway and not being especially warmed for the benefit of plants) will help us to keep productive plants going for longer. Case in point: my tomato plants in pots, salvaged for the last few fruits when I left my allotment last October and popped on the windowsill in the porch when we moved in here. These slightly straggly tomato plants have kept growing over the winter in a room that is not particularly warm. Now, I was rather surprised to see, they have flowered!
I am guessing I may have to give these tomatoes a hand with pollination by giving them a bit of a shake when I water them. I look forward to seeing whether they produce any worthwhile fruit. In the meantime, the cuttings from these plants are still in water and I hope they will form roots in the next week or two.