They shelter the first seedlings of spring and harbor the harvest well into winter. Greenhouses, once the domain of the professional gardener, are now popular year 'round with home growers and professionals alike.
But growing greenhouse plants requires more than placing pots in a clear building. A greenhouse must be put in the right place and its interior must be controlled to provide the right environment for plants.
Greenhouses should be placed in a sunny location as close to the south side of the house as possible, if not directly attached to it, says Shane Smith, co-founder of the Cheyenne (Wyo.) Botanic Gardens and author of the book, Greenhouse Gardener's Companion.
"When you're living with your greenhouse, the better you're going to take care of it," he says.
A typical home gardener usually can install a greenhouse kit (most commonly an aluminum-framed structure with double-thick plastic) in two weekends, depending on the type of foundation, which can range from a dirt floor to concrete, he says. Home kits generally range from 6 feet by 10 feet on the small end, to 10 feet by 16 feet on the larger end, with a price range of $750-$5,000.
Part of that cost depends on the glazing, or clear protective material, that you choose. Options include plastic, fiberglass, acrylics, polycarbonates, and glass.
All those glazings will do the job; what you choose depends solely on your preference. But no matter which glazing you choose, Smith recommends one with double thickness because it will contain heat better.
As for greenhouse size, well, buy the largest you can afford, he suggests. "The one thing I always hear is, 'I wish I'd bought a bigger greenhouse.'"
To ensure plants will set fruit, proper ventilation must be maintained, either passively with a few open vents or actively, using exhaust fans to pull air from lower vents.
Without proper ventilation, plants may grow well, but vegetables will not form, Smith says.
Proper temperature is determined by crop - 60-90 degrees for fruiting crops or 50-80 degrees for leafy crops. When more heat is required, most growers use electric heaters, although small natural gas heaters and wood burners also work.
Greenhouses generally should be kept at about 40-60 percent relative humidity, although those numbers are not as crucial as most think, Smith says.
High humidity, which occurs when the greenhouse is sealed, can lead to mold and fungus, so be prepared to open a window or two. If humidity is too low, simply water the walkway in your greenhouse, he says.
Though many gardeners use greenhouses year 'round, most use them primarily in spring because controlling excessive heat in the summer requires additional equipment, such as exhaust fans, and additional work. Others, however, use that intense heat for growing tropical plants, such as palms or ornamental banana trees.
"The greenhouse," Smith says, "allows you to follow your garden passions a bit more."
By Amber Stephens
photography by Jason Houston