How I Kept My Greenhouse Warm Without Electricity This Winter

I know winter is supposed to be cold, but I moved to the South to get as far away from the cold as I could. Seriously, *the* deciding factor for us leaving Colorado wasn't the expense of living there, or the tap water that you could light on fire, or even the wind so dry that you need a bottle of lotion just to get out of bed in the morning. No, we weighed the pros and cons like good, responsible adults and said "screw this" let's move somewhere warmer.

So, naturally, we moved to the south—where we've had, wait for it, unusually cold winters. Stupid irony.



Last week it had the nerve to get into the single digits with a windchill recorded at -5. This is the South, we don't do negatives here. Even our insults sound positive (bless our hearts). Negatives do not compute. So, of course, we all lost our minds.

After we set ourselves right by cleaning out the grocery stores of milk, eggs, bread, and peanut butter, we bundled into our little houses, washed our peanut butter & egg sandwiches (not a thing) down with milk, and crankily waited it out.

Not one for peanut butter and egg sandwiches (still not a thing), I spent most of my time running back and forth to the greenhouse to manically check on the temperature inside. In between trips, I came up with MacGyverian plans to keep it warm should the temps dip too far. I had a design for an outer greenhouse wrap made of tarps, bungee cords and duct tape... and a ginormous tea light / clay pot heater (which I hadn't quite thought through since my biggest clay pot is about 6 inches in diameter and I'm pretty sure no amount of duct tape would change that fact).

Keeping it warm

Because we don't have electricity running to the greenhouse, we had to find other (sciencey wiency) ways to keep it from dipping below freezing in there.

1. Use Thermal Mass
• The greenhouse floor is made of a 4-inch thick bed of gravel, which helps to absorb heat on sunny days. Yay us for planning ahead—although 6 inches would've been better.
• A 55 gallon drum filled with water (plus another 10 or 11 milk jugs filled with water) help to absorb heat during the day and regulate temperatures throughout the evening. We found our drum tossed on the side of the road, but Craig's list has tons of them listed fairly cheaply. You could also fill up a large trash can with water or a bunch of 5 gallon buckets. Paint 'em black for more heat absorption.
2. Insulate
• Because the walls are essentially made of thin plastic, I covered the inside with bubble wrap to help insulate and keep the wind out.
• Additionally, on colder nights, I wrapped pots in bubble wrap to help keep the roots from freezing.
• On the coldest nights, I covered plants completely in bubblewrap, creating a cloche or a greenhouse within a greenhouse.
3. Create reflective and black surfaces
• Along the north facing wall of the greenhouse, I put up a reflective bubble wrap (like the sun screen you use in cars during the summer to keep the steering wheel from melting your flesh). You can buy rolls of this stuff at the big orange or blue (or green) box stores. This helped to reflect sunlight back into the greenhouse.
• Having black (or darkly painted) objects in the greenhouse also helps to absorb heat.

Even with these efforts, my little 6x8 greenhouse dipped down to 27 degrees on our coldest day (which wasn't bad considering the negative temperature outside). Still, I lost one of my ferns, but everything else seems to be hanging in there.

We may have to eventually invest in a propane heater (or run electricity out to the greenhouse), but for now we're keeping it on the cheap and low.