Well, I'm in zone 7 (Raleigh NC) and we usually don't get really cold until Thanksgiving and then we warm back up for a few weeks of Indian Summer - but not this year. Some nights in the teens already!! daytime highs up to 40 degrees! Looks like its gonna be a long cold winter.
When I say I have a greenhouse, what I really mean to say is that I bought one of those hoophouse kits and built it on top of an old basketball court in the yard. Asphalt does a good job of soaking up sunshine and radiating heat over night but when the structure is 20 by 30 with a 15 foot tall ridge - asphalt can only do so much. A hoophouse does not seal up tight like a greenhouse so I have modified mine somewhat by stapling the plastic sheeting to lumber I screwed to the metal posts and mounding up wood chips along the base to stop air leaks under the edge. For heat I use an old wood burning stove with a blower unit attached. I can easily get a 20-25 degree gain from outside temps BUT, I have to tend to the fire every hour or so ALL NIGHT LONG. This gets about as old as de-tangling vines (and yes, I grow passionvines in pots so I know all about the tangle). I use a kerosene heater as backup which does a good job on a freezing night but it takes both heat sources on nights below 25.
It sounds like a hassle, but actually sitting by a roaring fire surrounded by tropical trees ain't so bad. Wi-fi will reach out there so I can play on my laptop in the evenings and it still beats hauling everything in and out of the basement.
Stay warm everybody!
