Photo: Min An

How much warmer is an unheated greenhouse than outside?

If done correctly, the greenhouse can stay an average of 20-30 degrees warmer than the outside temperature – even in the dead of winter!

rimolgreenhouses.com - 5 Low-Tech Winter Greenhouse Heating Techniques

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Cooler temperatures mean slower growth, and that is never welcomed news in the greenhouse. In fact, raising a plant’s soil by just 10 degrees Fahrenheit has the power to increase the plant’s height – depending on the plant – by a factor of two. That's why heat retention matters for growers looking to maximize efficiencies without spending their hard-earned capital on supplemental heating devices. Some growers will have the means to install an integrated environmental control system with an attached heating system. This is a fantastic upfront investment that will bring major dividends come harvest time. But for others, this may not be an option. The following are five passive heating tricks to maintain natural heat in your greenhouse.

Paint Them Black

This is a great option for growers with a little extra space in the greenhouse. Paint the outside of several 55-gallon plastic containers with flat black enamel. Smaller greenhouses can achieve the same effect with painted single gallon jugs or paint buckets. Place whatever vessel you choose in a place where it will receive the most sunlight possible throughout the day. The larger the bucket, the more heat that will be retained. As night approaches and temperatures dip, the heat captured emanates from the water and will warm your greenhouse or high tunnel. Only fill the buckets three-quarters of the way. If the buckets are sealed tight and heat to a certain temperature, there is the potential for the lid to blow off due to increasing pressure. If done correctly, the greenhouse can stay an average of 20-30 degrees warmer than the outside temperature – even in the dead of winter!

Compost For Warmth

Compost is a grower’s best friend. Finding just the right blend for your specific crops can take years to perfect. But beyond providing the essential nutrients to your plants, compost has another beneficial use: heat. The chemical breakdown that occurs in compost releases energy in the form of heat that can rise well above 100 degrees Fahrenheit. This benefits your heat-starved plants in the winter (and speeds up their growth). There are several ways to implement this low-tech technique. You can use more of those 55-gallon drums mentioned earlier or bales of straw.

Rescue With Row Covers

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This might be less creative than compost or gallon drums, but row covers – also known as floating row covers – can protect your plants from freezing. Just ask the team at Pleasant Valley Farms in Argyle, NY. This four-season operation uses both a Matterhorn Greenhouse and two Nor’Easter High-Tunnels. Even in the bitter cold winter, the family-run farm is able to grow produce. They credit the use of row covers and a constant monitoring of weather conditions to protect their plants at night.

Keep In The Heat

Ever heard the saying “did you grow up in a barn?” This applies in the greenhouse just the same. You generated this hard-earned heat through all the creative ways we discussed above. Now make sure that you retain that heat as much as possible. To do this, survey your greenhouse for any small cracks or gaps. Where you find either, apply silicone caulk to ensure that heat cannot escape. Duct tape is also an option for a quick-fix in a bind.

Heat Only What You Need

Separating space can save you valuable resources and maximize the efficiency of your greenhouse. Especially in larger greenhouses, heating the entire space can be a time-consuming, costly endeavor. First, group delicate plants and more hardy plants in different sections of the greenhouse. Then, erect a solid Perspex partition or create bubble wrap curtains to divide the space into more easily heated spaces. This is more economical and will allow you to control the temperatures to the liking of each plant that you grow. Four-season growing is a challenge – especially in hardiness zones 1-6. Without supplemental heat generated through oil or gas, it can be that much harder. But with these low-tech techniques it is still possible to generate much-needed heat for your plants all year round. Do you have your own low-tech ways for generating passive heat? Share the wealth in the comments below for other growers to use and profit from.

rimolgreenhouses.com - 5 Low-Tech Winter Greenhouse Heating Techniques