HEATING YOUR GREENHOUSE
by Carole Schwalm

Yes, you can use your greenhouse twelve months of the year it is just a little trickier to maintain the proper heat during cold weather. First, the minimum temperature (day and night) has to be between 60° F to 65° F to ensure plant growth. Second, a greenhouse loses heat 5 to 10 times faster than the same footage in your home. In this light however, having a working flower, fruit or vegetable greenhouse is worth it! Did I hear you say: “I’m in! Now what?”

No matter what type of heating you choose, take time early to address leaks all around the structure. Insulate if necessary or double-seal the structure if you do not have double-paned ‘glass’ area.

How much power is needed? For an average hobby-size greenhouse: 2,000 watt or 7.6 BTU to 3,000 watt or 10.2 BTU is recommended. Too much power and you risk too much heat and water loss similar to summer’s brutally hot days. Plants should not be blasted with the air flow. The use of benches elevates plants, and with the heater at floor level, they are protected.


ELECTRIC

If you have an electrical outlet, this type of heater is inexpensive to install, and you can also move it around as necessary, all you need to do is to make sure you are circulating the heat evenly.

Many electric heaters serve the purpose of heating for cold and cooling when it gets hot. Your heater should also be designed specifically for a greenhouse, not for in-home use.

Notes: The key to electric heaters is the need for a waterproof circuit. You should also turn the heater off when watering.

There could be a power failure and one hour of freezing is devastating to the plant world. Have a plan just in case.


INFRARED

Here, you are using waves that form electromagnetic energy. When waves hit something solid, like a cucumber plant, it absorbs the warmth. You can also put this type of heater close to the plant and it will not cause any harm. Using reflectors helps you beam heat where you want it.


PROPANE:

If you do not have electrical outlets to your greenhouse, propane is an option. The propane cylinder is the same type found with grills.

There are several key factors when using propane:
  • You need to keep the tank away from anything combustible.

  • You also need ventilation, because they can give off carbon monoxide. Without vent openings, you can also get a lot of condensation.

  • Most propane heaters do not have fans lessening the amount of heat. If you have very cold winter weather, and a larger greenhouse, you may find that propane isn’t your best choice.

  • To save costs you can partition off part of the greenhouse.