The Greenhouse Heaters are on high right now. It’s currently snowing here at our demo greenhouses in Grass Valley, CA. Typically, I let the kale deal with the cold temps on its own; but this year I bought a little 125,000 BTU to help get by. I also thought it would be an affordable heater for me to use when showing the greenhouses.
Ultimately I prefer the commercial style greenhouse heaters with venting and bigger tanks, but I wanted to experiment a bit with a more affordable option. Realistically, we’d prefer to have a radiant heating system in the greenhouse because when using this type of heat, 95% of the heat is concentrated to the plant. Radiant heating can be laid under concrete, under gravel, under benches, and even directly on the ground. Radiant/root zone heat can be used as primary heat while air-fired heaters can be a secondary source. In extreme conditions, some greenhouses need under the gutter heat.
Kale and spinach can handle pretty cold temperatures so we haven’t put much into greenhouse heaters for our demo unit. This fall I cleaned out the greenhouse, washed the grow bags, and replanted with new soil. Using Mr. Heater was my attempt to have the greenhouse warm enough to work in and run some tests. Before it started snowing, I heated the greenhouse air temp to 68°-70°. The soil temps were at 42° and the leaf surfaces were 55°. I’ve seen the opposite with root zone heat where it’s 30° outside and the root zone is 70° with an air temp of 55 and things were great! I can see now that the little heater here isn’t keeping up and the snow is accumulating on the roof of the greenhouse in some areas. I went ahead and rechecked the soil and it actually dropped 1 but the leaf surface remained near 55. I went over to the plants that were obviously getting hit with heat because they were swaying back and forth. The plants in close proximity to the heater had leaf surfaces only 3 higher at 58.
It’s clear the soil temps are the main focus for warming up a plant. The little heater can’t warm up 30 gallon grow bags efficiently for full plant support but they can definitely help melt snow. The funny thing is the spinach and kale look perfectly happy but I’m pretty sure production has slowed down. Soil microbes have trouble thriving in cold conditions so while they look good now, once we harvest the leaves, it will take some time to regenerate. Our seedlings have barely budged in a month’s time.
The last thing to consider is the gas emitted from greenhouse heaters. Most people imagine it’s carbon dioxide, but in most cases, gas (propane) heaters do not burn clean enough and emit ethylene and carbon monoxide. Proper venting is required and some plants can have a negative reaction to a constant flow of noxious gases. For greenhouses that aren’t being used in the winter, it’s better to remove the cover so that snow cannot accumulate. If leaving the cover on, be sure to heat the greenhouse to a minimum of 50 to help reduce snow loads. Snow loads for greenhouses fall under a different category than regular homes or buildings. Single wall greenhouses have a reduction rate that allows a lower snow rating if heated to required minimum temperatures.
Stay warm everyone!