Art Hegeman, of New Market, Va., heats his greenhouse year-round for the comfort of his prize cockatiels, as well as his collection of tropical plants and vines.

AP / Dean Fosdick

NEW MARKET, Va. This is prime growing season for the estimated 3 million gardeners who maintain greenhouses. Now is when hobbyists protect tender plants, gather seeds to start under lights, or bring in incubators to hatch chicks.

Chicks in a greenhouse?

“Sure,” said Michelle Moore, general manager of Solexx Greenhouses and Panels, in Salem, Ore. “It’s a little nontraditional, but some of my customers use them as brooder houses and aviaries.”

Greenhouses are emerging as more than protected growing spaces — they’re also incubators, science classrooms and even therapy rooms. Think of them as sunny lifestyle extensions.

Art Hegeman, of New Market, keeps a cockatiel in his gas-heated greenhouse, along with an assortment of flowering tropicals. “One seems to complement the other,” he said.

Moore has customers who raise exotic finches and rabbits, or even set up their greenhouses over ponds to protect turtles and koi from the cold.

“It’s kind of a ’60s throwback,” she says. “I had a customer write us recently saying he suffers from severe seasonal affective disorder [SAD] but began spending time in his greenhouse and it almost disappeared.”

Mike Helle, sales and marketing manager for Sunshine Gardenhouse, in Longview, Wash., installed one of the company’s greenhouse kits recently for the Make A Wish Foundation, a nonprofit that grants wishes to children with life-threatening medical conditions.

“It went to a young boy who had contracted leukemia,” Helle said. “The project spun out of time he’d spent in a hospital. He liked the food there so much, he decided to grow his own in a greenhouse.”

Many greenhouses are sold to elementary and secondary schools, where they augment natural science and biology lesson plans, and Helle said they’re also in demand for assisted-living facilities for the elderly.

Even those who use them for gardening can have ambitious plans.

“One person in the Dakotas grows his own coffee. His whole greenhouse is coffee [trees]. He keeps it hot and harvests beans all through the year. I don’t know how difficult that is to do but it’s pretty ambitious. I understand it took a few years to get any kind of crop,” Moore said.

Other customers have included a raw-food vegetarian, who grew only plants that could be eaten uncooked, and a man who heated his greenhouse into the 70s all winter to grow dwarf bananas.

Helle, meanwhile, enjoys spending time reading in his greenhouse, particularly when rain is spattering on the roof.

“A greenhouse is a great place to relax as the days grow shorter,” Helle said. “You can go into a greenhouse no matter what the weather and it’s always bright and cheerful inside.”

Hobby greenhouse gardeners “grow anything that you can grow indoors, from tropicals to vegetables to perennials and annuals,” said Janice Hale, with the Hobby Greenhouse Association, in Bedford, Mass. “Most start seeds for their outdoor gardens in late winter or early spring.”

Greenhouses can be made to run warm, moderately warm or cool, depending on their intended use. People who want to over-winter a collection of potted plants or root crops can place them in cool or frost-free greenhouses with nighttime readings bottoming out at 45 to 50 degrees.

Such things as kitchen herbs, dwarf fruit trees, strawberries and mushrooms require a slightly warmer greenhouse, with nighttime temperatures holding at around 55 degrees.

You’d better make it a jungle in there if you want to pamper tropical plants such as orchids, philodendrons and Bougainvillea while snow is on the ground. That means heating the greenhouse to at least 65 degrees at night and 70 degrees or more for at least a few hours during the day. Add foggers and pumps to build humidity to a clinging mist.

The cost of heating a greenhouse can be considerable. Heating systems also occasionally break down, and many gardeners have woken to the heartbreak of a greenhouse full of cold dead plants.

“The majority of hobbyists use greenhouses as cold frames, or as something for extending their growing seasons,” Moore said. “Some only do minimal heating, which can translate into wrapping a few strings of Christmas tree lights around specific pots.

“Properly equipped, you can grow many different things in a greenhouse, ranging from edibles to cut flowers, 365 days a year.” Gardening year-round

Gardeners turned wintertime couch potatoes? Not if you have a greenhouse.

Greenhouse gardening presents a different set of seasonal routines from the outdoor pastime. If you’re looking to extend your growing time, you can easily gain a couple of extra months to enjoy your blooms or let your vegetables mature by using a greenhouse. Let’s take it month by month:

January: Your greenhouse should be at its showy best. Snow may be piled up outside, but the container plants you chose to winter over are still flush with blooms. This is also a good month to start your new bulbs, especially daffodils, crocuses and hyacinths, or for rewriting weathered labels and readying pots for repotting.

Keep the greenhouse warm throughout winter, but be sure to provide the necessary ventilation.

“You want to be replacing the moisture-laden warm air, especially if it contains gas [carbon dioxide],” said Michelle Moore, general manager of Solexx Greenhouses and Panels, in Salem, Ore. “Exchange the air two-  to three times an hour. High humidity can mean a high disease rate if it isn’t controlled.”

February: Late February is a good time to get your seeds started if you want some maturity for a springtime display in your greenhouse, or want plants ready to go into the ground after the last killing frost. Many succulents are dormant, making it an easy time to clean them up, repot and check for insects. Those that are still growing should be watered, but sparsely.

March: This is a good month to get your vegetable seeds sprouting and encourage their growth under lights and over warming trays. That includes cabbage, tomatoes, cauliflower and lettuces. Check seed packets for countdown to planting outside so you start at the right time.

April: Springtime warmth begins to build this month, making it a prudent time to establish a watering routine. Insects also are beginning to emerge, so keep a wary eye out for mealy bugs and mites on your maturing or carry-over plants.

May: This is the month for transplanting all those seed-started flats into your garden. In Rhode Island, we usually consider it safe to plant outside around the Memorial Day weekend. It’s also the right time to add heat-resistant shielding to your greenhouse ceiling and walls to help diffuse the strengthening sunlight. Exchange your heaters for fans.

June: Start thinking about starting your second crop in the greenhouse, perhaps a late summer batch of tomatoes. Remove faded blooms and spent leaves from remnant plants, which will help reduce disease.

July: It’s summer cleaning time. The greenhouse is emptier now, which should provide enough elbow room for scrubbing things down — it’s amazing how quickly layers of pollen and algae can coat greenhouse walls and roofs.

August: Houseplants transferred to the greenhouse for a summer’s airing can be returned indoors late in the month. Note: Any plant you bring into the greenhouse can harbor hidden pests that can become out of control in the year-round warmth and humidity. Some gardeners consider their greenhouse a one-way operation — they don’t bring plants back in.

September: When the cooler days arrive, remove the summer shading you installed. Trim and prune whatever plants you choose to carry over. Glaze glass windows or plastic surfaces to eliminate drafts. This is a good time to start the so-called “winter plants,” like kale and chard.

October: Start shifting your favorite potted plants back inside the greenhouse to avoid damage from early frosts. Discard any plants that didn’t perform as well as you wished.

November: This should be a blooming, booming month in the greenhouse, with all those fall bulbs beginning their colorful display. Reduce the amount of water you give your plants from the drenching summertime norms. Over-watering kills more indoor plants than any other cause, and spreads many plant diseases.

December: It’s time to haul out those poinsettias and Christmas cacti you’ve patiently been tending. Catalog your successes and losses for the year so you can make wiser buying decisions once the seed catalogs arrive. Spend some reflective time sitting in the greenhouse and smell the blossoms on your Meyer lemon trees.