Many greenhouses are solar heated and runs much cooler in the winter months when heat is not supplemented. There are many types of cool loving plants that will survive the winter months if you do not want to supplement your heat and if you live in a grow zone that does not ‘go below’ freezing. The greenhouse is generally going to be fifteen to twenty degrees warmer inside than it is outside but in the night the cooler nights will mean colder temperatures that your plants will have to endure.
To fight back the cooler night temperatures and to keep your plants from freezing you can implement thermal storage of the solar heat for slow release all night long. You can use five gallon buckets of water (painted black and with a lid tight) to collect solar heat through out the day and this will release heat through out the night. If your outside temperature does not go below thirty degrees, this solar heat collection will work great in keeping your greenhouse interior temperature above thirty five degrees. If you find that your temperatures continue to drop below thirty degrees you may have to use supplemental heat in order for your plants to survive.
Some of the best plants that you can grow for the cooler temperatures are going to be your leafy plants. Houseplants, vegetables and you can still grow your fruit trees or bushes in the cooler temperatures as well. Usually you will find that other flowering plants or producing vegetable plants will be slow to grow but if you have a little more patience you could ‘get away’ with the cooler greenhouse and producing vegetables. As the outside temperatures increase the environment in the greenhouse will also increase where you will need to monitor your temperatures and remove the solar heat collection during the hotter summer months. You can take the lids off of your solar collectors to allow humidity and moisture into the air if you have a dry heat in the greenhouse.
During the falls months you will find that your greenhouse glazing will ‘do’ the solar heat collection for you, harnessing the heat from the sun and warming the inside of your greenhouse. This is how greenhouses are used to extend the growing seasons for plants, vegetables and flowers in many areas for gardeners. You can also use the power of the greenhouse to start your plants in the early spring when the soil outside is not right for planting yet, but you find your temperatures are ‘staying’ above the freezing point. Starting many of your garden plants in the greenhouse saves you time and money in creating a vegetable or flower garden.