Two nights ago, the temperature dropped to about 27 degrees Fahrenheit.
Rachel and I buttoned up the greenhouse for the cold, taped up any small rips and pieces of plastic, and stuffed pool noodles into the gaps between the front and rear double doors.
I opened the greenhouse yesterday to check on it and found that coffee, papaya, and other tropical plants were growing even though there was no additional heat other than passive heat provided by dozens of 55-gallon drums inside the greenhouse. Everything was fine.
That thermal mass alone was enough to keep the greenhouse cool enough to prevent frost. My coffee plants are the main indicator of whether the greenhouse is getting too cold. They were in their early 30s and damaged, but all looked green and happy after that cold night.
Last night was even colder, with an expected temperature of 24 degrees, so I also lit one of the small propane tank heaters I had placed in the front half of the greenhouse where I keep my coffee.
I checked on them this morning and they were all fine, even though they were on the floor where the cold was creeping in.
It probably would have been fine without the heater on, but I figured it was cheap insurance. We have about 70 coffee trees that we use to keep warm, and they are very valuable. Some of them aren’t big enough to flower or set fruit, and the idea of coffee produced in Lower Alabama is very interesting to me. I don’t really take chances because I want to see that happen. But it’s reassuring to know that they’re already experiencing 27-degree nights.
Barrels make a huge difference in keeping the greenhouse warm enough to avoid freezing on cold nights. It also prevents the plants in the greenhouse from overheating during the day, even if I forget to open the greenhouse and the sun is beating down overhead.
You can read more about this method and many other easy ways to grow tropical plants outside the tropics in my book Push the Zone.
Sometimes the simple things can make a big difference. There is no need for expensive heating systems, climate-controlled vents or other technological solutions.
Placing a barrel of water next to a sensitive young tree in your garden will have the same effect and prevent the tree from freezing on cold nights. Place the barrel next to the tree and cover the barrel and tree with a sheet to prevent frost from touching it. Keep it simple.
