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Gardens Under Glass



Season extenders are a necessity in the north and midwest. Whether they consist of plastic stretched over hoops, plexiglass propped atop bales of straw or the latest incarnation of the cloche, gardeners refuse to relegate their activities to the traditional May through September growing season.


The most luxuriant gift a gardener can give to him or herself is a greenhouse, conservatory or four-season room. These structures are built for the comfort of plants, but allow humans to enjoy time working and relaxing in them during the worst days of winter as well as in pleasant weather. Best of all, plant rooms allow northerners to grow palms, citrus, cacti and tropical treasures that ordinarily only do well in warmer climes.


Plant rooms need not be extravagant or overly expensive. Many of today’s building materials combine strength and high insulating values with economy and aesthetics. Turning a porch or deck into a four-season room, or adding a greenhouse or conservatory to a house need not be the extravagant task it was during the Victorian era, when glass houses were the purview of the upper crust during the Gilded Age.  Building materials such as aluminum, vinyl, and pre-engineered, tempered glazing offer structural strength, excellent R-values (insulating capabilities) and economy.


Siting the Room


A plant room needs to be sited in a way that permits the greatest amount of sunlight in, but also provides some respite during the hottest times of the day in summer.  South and west-facing rooms will capture the most light, but may also heat to extreme temperatures in the afternoon and evening. An east-facing room will capture morning light, but will be in shadow during the afternoon. A north facing room captures the least light.  Generally speaking, homeowners in areas that have long periods of cool weather would do best siting a sunroom with a southern or southwestern exposure. Gardeners living in hotter areas could use a room facing due east, northeast or northwest.


Sunrooms will also need some climate-control additions, such as blinds or shade cloth that will keep out the hottest rays of the sun in the summer, and a space heater or radiant heat system to keep the area warm during the winter.


Choosing Building Materials


The biggest investment in building a sunroom is in glazing and windows.  Several factors, including aesthetics and energy efficiency, need to be considered when choosing the perfect glazing for a sunroom.


The three main building materials that are used in sunroom and greenhouse construction are PVC or a PVC composite, wood and aluminum, and windows can be either wood framed, aluminum framed, or framed with wood clad with vinyl or aluminum.  Glass should be tempered or a safety glass, insulated and at the minimum, be double-glazed. For a room in which there will be furniture as well as plants, consider using Low-E glass. This is glass that has a thin coating of metal on the exterior side that prevents ultraviolet radiation from coming in and also prevents thermal transfer. This means that upholstery won’t fade and heat won’t escape in the wintertime; conversely, the room will also not heat to the boiling point during the summer.    For rooms built for the coldest climes, specialty glazing is also available. These options would include argon-filled windows or triple-pane windows.


Because washing windows is never anyone’s favorite chore, any selection should be maintenance-friendly. Most window manufacturers have built in helpful features, such as tilt-in or tilt-around capabilities.  Many windows also offer built-in screens.


Handling Humidity


The transpiration from growing plants, water-saturated potting mix and water features create a humid environment. This is great for the plant but creates problems for the homeowner. Excess humidity makes for condensation that fogs windows, encourages mold growth and any woodwork may warp or rot.  A well-constructed sunroom should be ventilated, at minimum with a simple oscillating fan. More extensive ventilation systems include louvered fans that push hot, humid air outside.  Humidity can also seep in through the slab flooring, so be sure that a vapor barrier is installed under the slab during construction. In addition, many builders will include a drainage system in the glass walls and the floor; this is especially needed if a hot tub, fountain or other water feature will be installed in the sunroom. The drain design releases excess moisture outside.


Planting The Sunroom


Adding plants and decor is the final step, and one that is open to the imagination.  For a dry room, cacti, succulents, palms and some of the unusual plants native to Australia are good choices.  Plants such as camellias, bougainvillea, pomegranites and citrus thrive in a subtropical room. Lush, jungle plants such as bamboo, bananas, and papayas grow well in rooms that have tropical conditions.


As with any construction project, it’s best to work with licensed contractors who come with good references, warrant their work and are willing to put any agreements they make in writing.  There are a number of excellent contractors and home remodelers who specialize in sunroom additions, so finding a firm with the expertise to build a dream sunroom shouldn’t be difficult. 

Look for books on greenhouse gardening and sunroom construction at