Commercial greenhouses use a lot of energy. Whether they are used to grow blooming geraniums in time for Memorial Day, tomato seedlings for the home gardener or fresh greens for Maine restaurants and grocery stores in mid-winter, it usually takes a lot of fossil fuel to keep greenhouses warm enough for plants to thrive.

Cozy Acres Greenhouses, owned and operated by Jeff and Marianne Marstaller in North Yarmouth, in July finished its first year operating a greenhouse which uses no energy from fossil fuels.

“Those signs say it all,” Jeff Marstaller said during a recent twilight meeting of the Maine Landscape and Nursery Association held at his business. The signs say, “Electricity from the sun. Heat from the Earth. Emissions at zero.”

The new greenhouse is 96-feet-by-30-feet. In a nearby field, workers installed a mile-long network of underground pipes connected to a geothermal heat pump. The electricity from 102 photovoltaic solar panels installed in the same field is used to run the heat pumps.

Marstaller said he turned the heat pumps off in late April, and doesn’t intend to turn them back on again until at least mid-October.

Because the greenhouse is connected to the power grid, Cozy Acres can sell electricity to the Central Maine Power Co. in the summer, when the greenhouse uses almost no electricity but is generating a lot because of the long days of sun. The greenhouse buys electricity back in the winter, when it uses a lot of electricity and generates little.

Over the greenhouse’s first year of operation, Marstaller said that the solar panels created 39,000 kilowatt hours of electricity. It used 29,000 kilowatt hours, and Marstaller said it is unlikely it will use 10,000 more by the end of the year.

Last winter, the coldest recorded temperature on the outside wall of the greenhouse was 33 degrees Fahrenheit, just above freezing. But the plants in the greenhouse stayed warm, despite it being the coldest winter in recent memory. The geothermal system provides heat through the greenhouse floor, so Marstaller put tents of clear plastic over the plants to trap it and use it most efficiently.

“It didn’t get below 40 to 45 degrees around the plants, and the temperature every day hit 55 to 65,” he said.

Marstaller uses his zero-energy greenhouse to grow microgreens and herbs, and he is looking for more markets for these products. Wild Oats in Brunswick is his only regular buyer so far. He hopes that when other restaurants and grocers learn that the products will be available year-round, he will gather more customers.

Building the new greenhouse was an involved process. The Marstallers originally approached the Maine Farms for the Future program for help in increasing their profits and received a $6,000 planning grant. Later, they won two federals grants, $48,750 from the Rural Energy for America Program and $5,000 from the Environmental Quality Incentive Program.

Cozy Acres still has seven traditional greenhouses, heated by propane, in which the company grows seedlings for nurseries and flower shops all over southern Maine. The business is wholesale only.

Marstaller said he couldn’t convert his traditionally heated greenhouses to net-zero energy because they have concrete floors and it would be too expensive to add a radiant floor heating system. He could expand the new greenhouse to double his space for less money than it would cost to build a new one.

“I’m not sure I’ll do it at this stage in my life,” he said, but added that is something he could do if future business warrants. He would move the long north wall farther north. Then he would have to build only the end walls and a roof, in addition to more solar panels and heat-pump capacity.

AT THE SAME Maine Landscape and Nursery Association meeting, Maine state apiarist Tony Jadczak spoke to the group about an attempt to ban the use of neonicotinoid pesticides on ornamental plants. Several groups have proposed a ban in response to concerns about the pesticides being harmful to bees. A neonicotinoid bill was submitted to the Maine Legislature last year, but later withdrawn.

Jadczak said he believes the problem with honeybee colonies has many causes, but that varroa mites, which began infesting honeybee colonies in about 1987, are one of the major factors.

While neonicotinoid insecticides can kill bees because bees are insects, he said, they are less harmful than the pyrethroid and organophosphate insecticides that the neonics replaced.

Jadczak noted that Australia, which uses neonicotinoids as much as the United States but does not have a problem with varroa mites, has no problem with colony collapse disorder.