A GREENHOUSE IS a splendid antidote to a Canadian winter. It's a little oasis, a piece of summer, or at least a temperate zone where plants can flourish, sheltered from the cold. A greenhouse is the ticket, whether you plan to raise exotic orchids year-round near Whitehorse, or grow cool-season vegetables for Easter dinner around the Niagara escarpment. But you'd need two different greenhouses to accomplish these purposes. It's important to choose the right greenhouse and plan carefully to meet your needs. Winters are notoriously harsh in Canada, but summers can be, too, especially for a delicate flowering plant trapped in an eight-by-ten-foot glass bubble. In its native home, it is warmed by the moderating effects of a nearby ocean, and cooled by its breezes. The glare of the July sun overhead at noon in Regina will be enough to cause the plant's buds to drop - or worse, if the stomates (pores) don't close fast enough. Kyle Exner, manager of B.C. Greenhouse Builders, fabricates greenhouses in British Columbia's lower mainland and ships them across North America. He says it may take longer to select the proper greenhouse than to build it. "You need to ask yourself some critical questions early on. Do I see myself tending tropical plants in December, or starting my bedding plants in January?" The cost of a greenhouse will depend partly on its purpose and partly on how much time the gardener plans to spend in the structure, Exner says, adding, "Most of the greenhouses we build are 12 by 16 feet, or smaller. Most are of energy-efficient materials, and most will be a permanent addition to a yard." In B.C.'s lower mainland or along the shores of Lake Ontario, south of Hamilton, a four-season greenhouse is possible, thanks to a single layer of glass, or a six-millimetre sheet of light-weight, shatter-resistant polycarbonate. A heat-cured plastic, it is best known as the substrate for compact disks, and in plastic eyeglass lenses. It is the material of choice for building the modern hobby greenhouse. Exner says he still sells a lot of single-pane glass for greenhouses in southern B.C. and on Vancouver Island, but most of his customers opt for more than one layer of glass, to reduce winter heating costs. And the majority of his customers choose polycarbonate. Twin-wall polycarbonate takes advantage of air spaces sandwiched in large cells between two sheets of plastic. In colder climates north of Toronto, in Quebec, in most of the Maritimes and in the British Columbia interior, this will create a greenhouse capable of fending of all but the harshest conditions. On the Prairies, in northern B.C. and any other region where the mercury drops below -20 C for more than a day or two each year, it is advisable for greenhouses to have triple-wall polycarbonate - especially if one wants to cultivate orchids or fruit-bearing plants. "In those climates," Exner says, "you can over-winter begonias and fuchsias with only a small electric heater and a twin-wall glass or polycarbonate greenhouse. With a larger heater, you can grow cold-season vegetables all season. If you want tomatoes in January, then 16-millimetre, triple-wall material is for you." The cloudy quality of polycarbonate reduces the need to cover the roof with a cloth to keep out the burning rays of the sun during the summer months. For a similar price but a clear view, twin-walled tempered glass is available. Those new to greenhouses should pay particular attention to the roofing material. "Your roof is where your major heat loss takes place," Exner says. Typically, it's also where solar gain needs to be reduced. His company offers a roof made of triple-wall polycarbonate. This material admits only 75 percent of the light that strikes it; with glass, it's nearly 100 percent. With glass, the owner gets a view, moderate heat efficiency and a showpiece for the property. Suitable heat and other utilities for the greenhouse must also be carefully planned. Electricity is critical, and running water and natural gas are useful. Fans control dreaded condensation, and lighting convinces plants that the warm weather is a product of the longer days they would enjoy if they were rooted closer to the equator. Having invested in the building itself and the plants inside, a greenhouse hobbyist will do well to select adequate fans for the structure. A hardware store propeller fan will meet most growers' needs, but to ensure mildew and moisture control, a horizontal airflow fan is necessary. Mounted near the ceiling, this type of fan encourages plant growth by increasing carbon dioxide availability and promoting uniform temperature from floor to ceiling. Adding a season or two to the gardening year means adding some daylight. There are several ways to accomplish this, Exner says. One can add specialized, full-spectrum fluorescent bulbs to a light fixture. Another approach is to purchase one warm-colour temperature fluorescent bulb (yellow) and one cold-colour temperature fluorescent (blue) to use in the same lighting fixture. This is an economical way to create a full-spectrum light: each bulb costs about $4, whereas each full-spectrum bulb costs $30 and up. In either case, an inexpensive shop light fixture to hold the bulbs costs about $18. "If you are growing high-value exotic plants, you will be choosing high-pressure sodium or metal halide lighting," Exner says. There is growing interest in horticulture, and greenhouse owners have many high-end lighting choices available at the flick of a switch, says Patrick Vivian, of Sunlight Supply Inc. in Vancouver, Washington. The lighting manufacturer builds and distributes lighting systems for commercial growers and hobbyists. The technology once available only to industry is being adapted for much smaller operations. "There has never been so much choice in the market," Vivian says. There are small, high-pressure sodium systems for a few hundred dollars. By contrast, the top-of-the-line lighting strategy uses a combination of light from red-spectrum sodium bulbs and from blue-spectrum high-output T5 fluorescent bulbs. After determining how much greenhouse you want, the next decision is where to place it, Exner says. Attaching it to the home is the most efficient, inexpensive option. Builders agree sharing utilities and a common wall can save $2,000 to $4,000 in construction costs on the average greenhouse. A stand-alone structure will require buried utilities trenched in from the house. Greenhouses require firm foundations. If glass is used for the walls, a concrete base is mandatory to prevent shifting and breakage. At a minimum, a four-by-four or four-by-six cedar grade beam is needed over a packed clay and gravel base. New pressure-treated woods should be avoided because they contain copper, a substance that will corrode aluminum, a common component of greenhouse frames. In softer soils or where soil is well frozen in winter, concrete piles will be needed to anchor and support the structure. Many greenhouse owners opt for a concrete pad and short pony walls to add height. This provides an easily washed and maintained floor surface as well as a sturdy foundation. In addition, concrete is easily sterilized in the event of a plant disease infection. "If it gets into your dirt floor, it is a real problem to get rid of," says Exner. Most hobby greenhouses arrive as do-it-yourself kits, but contractors will assemble them for a fee. If a contractor is providing all the labour and when benches, lighting and utilities are included, a buyer can expect to double the cost of the greenhouse, Exner says. "You can reduce that dramatically depending on how much of the work you do yourself. A lot of country homeowners like to do that sort of stuff on their own, so they can add a good deal of sweat equity to their project." However, a greenhouse owner doesn't want to experience excessive sweating, especially in summer. Most greenhouses have roof ventilation systems and automatic pressure cylinders that open these vents when the temperature reaches anything above a simmer and close them as the room cools. Additional wall vents and fans can be added, especially in larger greenhouses, where heat buildup can occur swiftly, even on a mild February day. When the sun's heat is inadequate, supplementary heat is required. "If you are planning a greenhouse and will be bringing in water and electricity and natural gas is handy, put it in," Exner advises. "You will spend a lot more up front and get it all back before you know it, when you don't have to run that electric heater you plug in day and night." One way of moderating the temperature is to sink large plastic barrels filled with water, crushed rock or both below the floor of the greenhouse. These heat sinks will take in energy during the day and release it at night. Properly situating the greenhouse will also reduce the amount of light and heat required to operate it. A southern exposure is best, although east and west will also work. A greenhouse close to the house will reduce utility runs and facilitate trips to the washroom. If the hobby sticks, an expansion may be desired, so the location of the greenhouse should allow for one end to be extended. Most greenhouse systems provide for additional panels to be added, with the end wall moved out to accommodate an addition. Category Good Better Best R-value Single-wall glass. Double-wall glass, walls and roof, or double-wall polycarbonate. Triple-wall or multi-cell polycarbonate, walls and roof. This is the most efficient combination of all. For the best view with better efficiency, install double-wall glass with triple-wall polycarbonate roof. Utilities Garden hose water supply for three seasons and a water bucket in the winter. Electrical for light-duty fans and small power tools on an extension cord. Water and electricity underground from the house for in-greenhouse use throughout the year. A small sub-panel supplying power for lighting, fans and heater during the winter. Water and electrical as above, plus natural gas for heat. Natural gas costs more initially, but saves money over electricity in the long run. Foundation Compressed gravel over clay, suitable only for smaller polycarbonate greenhouses. Cedar 4 x 4 grade beam over compressed gravel. Concrete piles in soils prone to freezing and shifting. Concrete floor and foundation, piles as necessary. Concrete removes the risk of disease persisting in the floor soil. Frame Plastic. Prone to bending, it can be very durable otherwise. Easy and light to assemble and modify. Doesn't accept paint well. Lacks strength for hanging baskets, fans and other equipment. Wood. Strong, excellent construction material. Heavy, and unless it's pressure treated or cedar, it is prone to rotting. Aluminum. Light and strong. Cost is similar to wood. Works with proprietary building systems. Available in many colours. Very strong for mounting interior hanging accessories. A high-quality, entry level eight-foot by 12-foot polycarbonate greenhouse, framed in aluminum, costs $3,500 and up. Double-wall polycarbonate will add several hundred dollars to the price. A high-end, triple-wall polycarbonate or double wall glass with a polycarbonate roof costs about $5,000. Annual operating costs could range from several hundred dollars to $1,500 or more. This takes into account geographic and weather variables, preferred crops, the size of the greenhouse, the type of panes chosen for the structure, and the type of heating used.