This is the temperature yesterday morning - 2 and a bit degrees! And I'm in sunny Auckland. I have tomatoes in there and they are (amazingly) starting to flower. Not sure they will survive if the temp swings between 2 and 20 (which it gets to on a good sunny day) though. The bell pepper plant I rescued from the chilly garden seems to like things, it's fruiting. And the chilis are doing OK, but all they have to do is survive.
- I've tried burning candles under terracotta pots, which probably lifts things by a degree or so at most, and is very localised in effect.
- I've also put fruit juice bottles full of water around the planter boxes, for thermal mass. Not sure if that's making a difference, to be honest.
- I'm looking for lots of cheap bubblewrap so I can insulate the roof.
- And I am thinking about rigging up some sort of solar thermal system (once I finish building my chicken coop, and if I can find cheap bits to do it with). Not absolutely sure what I'm doing with this though, but hey, how hard can it be? :)
Any other ideas for very cost-effective greenhouse heating?