Facing Fall and Winter in the Heated Greenhouse

By Roger Marshall, "The Greenhouse Grower"

In my 300-square-foot heated Rhode Island greenhouse the banana trees are pushing out leaves as fast as they can. They seem to know that winter is not far away, and they want to be as large as possible before the cool season comes and growth slows or stops. Yes, I do get bananas from them, but of more importance to me as the home cook are the banana leaves. Adding a good sauce and wrapping most meats in banana leaves makes the meat more tender, juicier, and tastier.

The heated greenhouse also contains a number of citrus trees. I grew enough oranges to make marmalade last year. I also have lemon, lime key lime, and olive trees in the greenhouse. Frankly, there is nothing quite like picking fresh key limes in January or February and making a fresh key lime pie for dessert. It’s almost like living in Florida without the hassle of airplane travel.

You might ask how much it costs to heat the double-paned greenhouse all winter. If I were growing only bananas, the costs would be prohibitive. For example, I figured that I spent more than $200 heating the greenhouse the first winter I grew a banana plant. I got two hands of bananas that in a supermarket would have cost just a few dollars! But if the cost of heating is shared between all the plants – the citrus trees, the herbs, the flowers (dahlia, mandevilla, clivia,), the numerous seed flats in spring, and the overwintering hanging baskets – the cost becomes much more realistic.

Heating with propane appears to be the least expensive method, and I have found that my greenhouse needs about 18,000 btus. That means a forty pound propane tank a week during January and February, and monthly during other cold months.

There are a few strategies that can be used to reduce greenhouse heating costs. Probably the most well-known one is to staple Bubble Wrap™ around the inside of the greenhouse, and to cover the plants with a spun fleece. I figure that the use of these materials moves the greenhouse up one gardening zone.

Alternatively, you can cover the entire outside of the greenhouse with clear ShrinkWrap™. ShrinkWrap™ is a plastic film used for covering boats that shrinks taut when gently heated with a propane flame. Just staple it in place on 2x4s installed over the greenhouse. The tightness of the membrane reduces heat loss to the outside and cuts heating costs by about 15% to 20% compared to years when I have left my greenhouse uncovered. ShrinkWrap™ can be found online here. In spring, the product can be removed and recycled.

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