Find Sanctuary in a Greenhouse

This rooftop greenhouse by Hartley Botanic Inc., still under construction, measures roughly 13 by 20 feet and is the ultimate urban getaway. Photo supplied by Hartley Botanic, Inc. 

Precisely because it defies the season, greenhouse gardening is a pure sensory delight that a growing number of urban dwellers are opting for as their garden amenity of choice.

Why own a greenhouse? Anyone who has visited the U.S. Botanic Garden’s glass house in January knows how good it feels to smell the warm, moist air, feel the sunlight filtered through lush green leaves, smell the tropical orchids, and hear the gentle sounds of water fountains.

There are many horticultural reasons to add a 50 to 100 square-foot greenhouse to your yard, your deck, or even your rooftop. You can extend the growing season for herbs and edibles and get a jump on starting spring seedlings. Eating fresh salad you’ve picked yourself in February is a delight. I’ve done it, I know.

If you’ve got a horticultural specialty, a greenhouse can be your cactus, succulent, or orchid clubhouse. It can be a place to share your love of gardening with your children. The elderly can garden easily in a greenhouse, either sitting or standing. Electronically overstimulated people of all ages can find peace in this quintessentially analog environment. It’s a safe and contained personal space – a true sanctuary. And besides, it’s not too hot, not too humid, and mosquito-free. I love walking out of the house into the cold, and entering my 85-degree greenhouse where I might knit or take a catnap in the sun.

Humans have always attempted to control their horticultural environment. Reclusive poet Emily Dickinson had a greenhouse built onto the south side of her family’s Massachusetts home. Even Matt Damon, in “The Martian,” tried his hand at extraterrestrial greenhouse gardening. It’s a universal urge, and thanks to several manufacturers and importers one that may now easily be satisfied for gardeners on almost any budget.

Getting Started

Usually the smaller the greenhouse, the easier it will be to find a suitable site. According to “Charley’s Tips” at http://www.charleysgreenhouse.com/index.cfm?page=_tips, your greenhouse should ideally receive six or more hours of winter sun per day. The long side is best angled toward the winter sun. In warmer weather, shade will be needed, either from greenhouse shade cloth or from a nearby tree. Shade cloth is readily available from your greenhouse manufacturer, such as Winter Gardenz (https://www.wintergardenz.com/store/p21/Shade_Cover_Kits.html), or mail ordered from a company like FarmTek (http://www.farmtek.com/farm/supplies/ExternalPageView?pageKey=EXTERNAL_PAGE_3001). I have had several Capitol Hill clients install shade cloth in summer above their garden pergolas, bringing down temperatures 15 degrees even without any overhead plants. My own greenhouse is shaded by a nearby oak in summer. When it loses its leaves in winter the greenhouse receives plenty of sun.

In urban settings, say on a Capitol Hill corner lot, greenhouses can be three-sided like a lean-to, sharing one exterior brick wall. This has the added benefits of wind protection and of daytime heat from the brick radiating out after sundown to moderate cooler nighttime temperatures.

Greenhouses are relatively lightweight, so deck installations are no problem. Rooftop greenhouses are also an intriguing option. Just as with a rooftop air-conditioning unit, you would span the width of the roof with two steel I-beams and attach the greenhouse to that frame, thus keeping the weight off the roof surface. If you already have a roof deck, bolt the greenhouse to it. According to Roger Fitness, managing director of Winter Gardenz greenhouses, “It’s helpful to install tile over wooden roof decking to prevent cold air from entering between wooden deck slats from below.” Fitness advises customers installing his company’s greenhouses on urban rooftops. As always, check with DC’s Department of Consumer and Regulatory Affairs, http://dcra.dc.gov/service/get-building-permit,to see if you need a permit. If you live in the historic district also check with the Capitol Hill Restoration Society, http://chrs.org/history-and-preservation/chhd-map/,before making a purchase.

If you’re installing a greenhouse in your backyard, just set it down on level ground (as I did) or stake it at the corners. You can build a pressure-treated wooden frame or a brick frame, or even pour a concrete slab onto which to bolt your greenhouse. An excellent foundation guide may be seen on the Winter Gardenz website, https://www.wintergardenz.com/store/c13/Foundations.html. Obviously your choice would depend on your commitment to both your house and your greenhouse gardening future. In the case of Hartley Botanic, http://www.hartley-botanic.com/, owners often dig brick or stone foundations as these greenhouses are built to last up to 75 years.

Other Design Decisions

Once you’ve determined you have a viable site and selected the size, orientation, and attachment method, you must choose a glazing material. Greenhouses come in the traditional glass or in polycarbonate. Polycarbonate has excellent thermal efficiency, is lightweight, and costs less. If made from a reputable source, not of recycled materials, and UV treated on both sides, it should last 15 years. For a good side-by-side comparison between glass and polycarbonate see https://www.wintergardenz.com/glass-vs-poly.html.

Other options would be motorized shade, heat, and ventilation systems. I have none of these and enjoyed several years of successful greenhouse growing. However, I do work from home and can monitor and easily adjust my greenhouse door and vent for variable weather conditions.

Cost

You get what you pay for with greenhouses, from a $700 Costco 6 by 8 foot model all the way to the high five figures (or more) for an English made Hartley Botanic glass house, installed by their expert North American crew. Several of these have been built in the DC metro area. Says Hartley Botanic Vice-President Shelley Newman, “You’d be shocked at how many baby boomers are giving these to themselves as presents. Many choose greenhouses instead of swimming pools.” So if you’re settled in for the duration and it’s an option, treat yourself to this greenhouse which is really more like an addition to your living space than a utilitarian amenity.

Another option, for somewhere between $2,000 and $4,000, is a polycarbonate greenhouse by Winter Gardenz. Made in the US, it is shipped to you or your local contractor for fairly easy on-site assembly. The gaskets are very durable, more so than those in my Costco model which I’m always poking back into their grooves. The doors, window vents, and shelves are nicer too. Roger Fitness and his staff will be on hand by phone to walk you through installation. This option would be the most reliable and cost effective for beginners.

What to Grow

Salad greens and herbs are great for first-time greenhouse gardeners. I’ve also grown radishes and turnips, and have started all my spring flower seeds in my greenhouse. One year I grew wheatgrass, which is fast and beautiful and great to throw in your juicer. Purchase a good soil mix from a local garden center. You don’t need deep soil to grow these plants in a greenhouse. After my first year using deep, heavy ceramic pots I switched to shallow plastic trays which were fine for my arugula, spinach, mache, and lettuce. When you water every morning, shallow pots will be easier to manage. Keep a thermometer inside, and know when to open the roof vent and door so your plants don’t overheat. Even in my unheated Costco greenhouse temperatures did not go below freezing when nighttime temperatures dipped below 20 degrees.

Greenhouse gardening is a great way to stay in touch with the seasons, especially winter when we are outdoors less often. Let me know if you take the plunge so we can compare notes!

This drawing of a 6 by 8 foot Winter Gardenz greenhouse shows the glazing panels, sliding door, vent, and ground stakes. Drawing by Winter Gardenz®
Step inside the greenhouse to another season. Photo by Winter Gardenz®

Cheryl Corson, RLA, ASLA, is a landscape architect and dirt gardener who designed her first Capitol Hill garden in 1998. She enjoys helping homeowners and business and school clients with garden, landscape, and playground projects. See www.cherylcorson.com.


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