Okay, call us wimps. It’s gets a couple of degrees below freezing and we think we are in the high arctic. But, this is the Central Coast of California – it’s not supposed to freeze, or at least, not very often. In any case, we grow year-round, and some of those crops really don’t like the cold.
Thus, the hoop house, aka high tunnels. They do a great job at capturing and holding heat during the day, but aren’t very effective at keeping out the cold at night. If our min-max thermometers are to be believed, it’s actually been a couple of degrees colder in the hoop house than outside, although I can’t explain why. In any case, this is all fine when the night-time lows are above about 30° F, but they have for the last couple of nights gotten down to about 26° F.
Our long-term strategy is to build a rocket heater in each house. We have more than enough naturally-fallen wood to keep them going through the coldest of winters. But, since we haven’t built them yet, we had to resort to this:
That’s a little infrared heater sitting atop a 20# propane bottle. The first night we tried these, they helped a bit, but not really very well. The second night, we placed a fan behind them, and the results were great. The inside temperature was between 4 and 7 degrees F higher than outside.
Of course, given the price of propane, not to mention the non-sustainability, this isn’t going to deter us from doing the rocket heaters:
In the morning, the outside crops were pretty well frozen, but were just fine when the morning warmed up:
Many plants produce a natural antifreeze that allows them to tolerate below freezing temperatures. It also seems to make them sweeter – “kissed by frost.”
–posted by Steven