The winter greenhouse – to heat or not to heat? That is the question!!!

Should you heat your greenhouse in the winter?

We all want to use our greenhouses in the winter. But, it can be costly to heat them all winter long. For certain crops you will need the heat. Do you want to grow seasonal  winter crops without the cost of additional heating? Or, do you want to pay the heat bill to have tomatoes and peppers all winter long? That is the real question.

Did you know that a greenhouse will build up a lot of heat during the day? That is why you need a ventilation system in place. But, once the sun goes down the heat will begin to dissipate and disappear. In order to keep your greenhouse above the outside temperature at night you will need to have heating systems or other solar systems in place.

Solar Practices

You can keep some heat in your greenhouse at night by using a few solar practices. You can pull a solar blanket over the roof of the greenhouse to help keep any heat inside. These are on the inside of your greenhouse and are typically a heavy blanket that can be pulled at night.

Probably the most popular and easiest method is to use black containers filled with water. These will build up heat during the day and let off the built up heat slowly through the night. You can use gallon water jugs painted black or 55 gallon drums.

You can put a compost pile in your greenhouse. Although, I have heard quite a few people complain about the smell. If you have a properly balanced and properly functioning compost pile you should not have these odors. But, if you want to spend some time and money you can put your compost pile outside and pipe water through the pile (which will heat the water in the pipes) and through the greenhouse for heat.

Some people will use a layer of bubble wrap (yep, like what is used for packing in all the boxes you receive) to help add insulation to their greenhouse. They basically just line the interior with the bubble wrap to help keep the greenhouse a little bit warmer.

These methods will all give you supplemental heat, but none of them will give you a way to control what end temperature you require. To set the heat at let’s say 60 degrees, you will need a heater with a thermostat.

Heating systems

Greenhouse heating systems are available in electric, natural gas and propane. I much prefer the natural gas or propane. My top pick, and the heater that I use in all of my personal greenhouses, is the Southern Burner heater. I have used both the natural gas and the propane models. I find that they both function the same. These are great heaters because they require no electricity. They are the perfect size to fit under a greenhouse bench, thus staying out of the way and not using up valuable space. There is a vented and a non vented model. I personally have always used the non vented heater, but there are some locations in the US where this is a problem and against code. Even though it is called a non vented heater you still need to have a fresh air supply.

Max/ Min Thermometers

A relatively inexpensive, but very valuable tool is a max/min thermometer. These can go from low tech models to models where you can monitor the temperatures from inside your home. Some even have an alarm system set up with them if the temperature drops too low. These are valuable in both a heated and unheated greenhouse to help you troubleshoot any potential problems that you may have.

Crops You Can Grow in a Heated Greenhouse

You can grow just about anything that you can grow in your garden in the summer if you heat the greenhouse. Your night time temperature for tomatoes must be a minimum of 55 degrees. You can also grow peppers, squash, cucumbers, melons, beans, eggplant, corn, basil, tomatillos, etc.

Rules To Growing in an Unheated Greenhouse

If you are growing in an unheated winter greenhouse there are a few rules you should follow for the best harvest. You must be growing crops that are in season during the winter in your area. These cool weather crops include crops such as lettuce, spinach, chard, carrots, etc. Do NOT try to grow warm weather crops in an unheated winter greenhouse. If you are not sure of your growing seasons I would check with my local extension office to see if they have a free vegetable planting guide available. If you don’t know where they are just do a search for extension office “my town”.

Do not try to grow in containers. They will lose any heat they have retained rapidly. You should grow in  the ground or in raised beds.

Cut back on how much water you think the plants will need. Plants require a whole lot less water in the winter than they do in the summer. Only water when the ground is dry 1″ to 2″ below the surface.

Grow in “layers”. Add a cold frame or a mini hoop house inside the greenhouse. If you have electricity you can even add heat cables to the cold frames or under the mini hoop house. I always like to use heat cables in  my personal cold frames. I  find that it gives a higher yield earlier. Just be sure that you check these in the morning. Depending on your location and your weather your cold frame or mini hoop house made need to be opened during the day and closed at night.

Crops You Can Grow in an Unheated Greenhouse

You can typically grow lettuce, spinach, radishes, carrots, beets, turnips, kohlrabi, broccoli, cabbage, bok choi, chard, greens, mustard greens, kale, chives, chinese cabbage, english peas, and cilantro (may require a double layer growing system such as the cold frame).

In Conclusion

To heat or not to heat? Well, that is really your decision and should be based on how much money you want to spend for winter heat and what crops you want to grow. Whichever way you go, fresh veggies year round can’t be beat! Enjoy!