Robin Sweetser

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Robin's greenhouse Potted azalea plants, often given as gifts, are not cold hardy but will blossom all winter in the greenhouse. Slipper orchids grow and flower year round, producing impressive blooms on a small plant. Fibrous-rooted begonias flower all winter in bright indirect light, while tuberous types eventually drop their leaves and need a rest. Chrysanthemums will re-bloom if cut back after flowering.

For more than thirty years I had longed for a greenhouse. An incurable plant collector, I am constantly rooting cuttings and trying to raise new plants from seed. After years of trying to cram all my plants onto a few sunny windowsills, I needed more space for year-round gardening.

But I wasn’t quite sure what kind, how big, and who would build it. Couldn’t we just fashion some funky but functional greenhouse out of scrap lumber, plastic, and those old wooden storm windows I’d been collecting?

After doing some serious research, we added on a nine-by-twenty-foot, two-story, aluminum-framed, double-paned glass greenhouse. We refer to it as our Caribbean vacation, but it was in the price range of ten vacations! However, the heat we gain from it on a sunny winter’s day is as valuable as the amount of growing space it affords; I hate traveling, but whenever I am in need of a rejuvenating shot of heat and humidity, all I have to do is open the greenhouse door and step into another world. It is a sure cure for the winter blues.

Outside, the flower garden may be bare, but in the greenhouse we are blooming up a storm. Bright red geraniums blossom year-round and seed-grown begonias—both tuberous and fibrous—reward me with red, white, orange, and pink flowers. Every fall I try to rescue a windowbox or two since many of the plants are tender perennials. Cutting back and fertilizing them encourages regrowth, and eventually they’ll blossom again. In the spring they are ready to go outside and begin a new season.

Within the glass walls, amaryllis bulbs are starting to show signs of life, but probably won’t be blooming in time for Christmas. Chrysanthemums always do well in the greenhouse and we have some mini-azaleas that bloom in late winter. Dwarf citrus plants—two Meyer Lemons and a key lime—have blossomed and set fruit. African violets and streptocarpus are still setting buds, and a hanger of yellow jasmine scents the air. Scented geraniums are one of my passions but it is the orchid family that keeps me thoroughly entertained; there is always new growth, elusive buds, and new aerial roots appearing. All visitors are taken on the “orchid tour,” whether they want to or not.

Technically speaking, our greenhouse is considered a cool conservatory because night temperatures can drop to 45 degrees, but since it is two stories tall we have some leeway in positioning the warm-loving plants at a higher level and placing those that can take the cold nearer the glass. Double-paned glass keeps the greenhouse from losing too much heat at night while still allowing it to warm up comfortably during the day. In summer, nearby maple trees shade the greenhouse all afternoon, keeping it from overheating. Windows, doors, and a skylight vent excess heat and bring in fresh air.

As if that wasn’t enough growing space, we also have a fourteen-by-twenty-four-foot, plastic-covered hoophouse that we use to grow spring seedlings and extend the gardening season at both ends of the calendar. We try to grow greens as late into the winter as possible and have used the hoophouse to harvest fine crops of cold-hardy lettuce and Asian greens until Christmas in milder years. Since it has only one layer of plastic, the hoophouse suffers from wide temperature swings. On a sunny day the heat rises greatly, but at night the hoophouse can cool off to within 10 degrees of the outside temperature. We create microclimates within the hoophouse using row covers, hay bales, water-filled containers, and even a small cold frame, but eventually the plants succumb to frigid temperatures. I still keep a path shoveled to the hoophouse all winter however. On a sunny mid winter’s day, temperatures inside can reach the 80s while the outside is windy and cold. Off come the sweaters and boots, out come the lawn chairs, and we get a refreshing mini-vacation without having to stand in line at the airport.

Is there a greenhouse in your future?

If you are planning a greenhouse project, here are some points to consider when choosing the perfect structure:

• Purpose—What do you plan to do with your greenhouse? Use it as a season extender or year round? Will you grow plants directly in the ground or in containers?

• Site—Will it be attached to your home or free-standing? Is the area level? Does it get enough sun? Are there trees that should be removed first?

• Style—There are as many types of greenhouses as there are companies that sell them. Hoophouses or high tunnels are made from plastic or metal pipes bent into a round or gothic arch shape and covered with UV stabilized plastic. Traditional looking greenhouses are framed in wood or aluminum and glazed with polycarbonate, acrylic, or glass.

• Size—Everyone says to get the largest greenhouse you can afford because you will soon fill it and wish it were bigger, but it is more practical to plan the amount of usable space different sized houses will give. Biggest isn’t always best.

• Skill—Can you realistically build a kit or will you need to hire a carpenter?

• Foundation—Glass greenhouses need sturdy masonry foundations. Lightweight plastic covered greenhouses can be built with wooden bases and most hoophouses are attached to pipes driven into the ground.

• Heat—Greenhouses heat up rapidly on a sunny day and cool off fast when the sun sets. Double walls—whether glass, polycarbonate, acrylic, or two layers of plastic sheeting with air blown between them—will help to moderate the highs and lows. If you plan to grow year round you will need supplemental heat.

• Ventilation—Doors, windows, vents, and roll-up sides all help to get fresh air into the greenhouse while exhausting hot, stale air. Thermostatically controlled fans or solar-powered vent openers help regulate temperatures.

• RESEARCH—Visit a greenhouse similar to the style you're considering. Ask the owners what they like and dislike about theirs and what changes they'd make. Before starting any building project be sure to check your local building codes and zoning rules and get the necessary permits.