Greenhouse Gardening

How to Choose the Best Greenhouse Kit

You can build your own greenhouse and bust the winter gardening blues. Our helpful tips will guide you in choosing the best kit to build your own greenhouse.

By Shane Smith
April/May 2013

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Curved eaves on the author’s first backyard greenhouse shed the snow of many Wyoming winters before being replaced with a more energy-efficient model.

Photo By Shane Smith

People who love gardens also love greenhouses. The best backyard greenhouses feed the need to dirty our fingers while the rest of the garden is dormant. Even a small greenhouse can provide effective season extension by jump-starting seedlings in spring. When managed properly, a greenhouse is a backyard oasis that yields fresh food year-round.

If a lack of construction skills is keeping you from building a greenhouse, consider a kit. The best greenhouse kit is one that fits your needs and your pocketbook. Kits are easier than building from scratch and don’t require as much building experience (although it certainly helps to have a DIY attitude when you set out to build your own greenhouse, even from a kit).

Shopping for Your Best Greenhouse Kit

Local Regulations. Start by researching required permits, zoning, setbacks, underground utilities and other requirements for your area. Some localities demand a certain type of foundation. A greenhouse attached to your home will likely face more stringent requirements than a free-standing greenhouse. In some places, greenhouses are regulated under a “storage shed” designation. Consider size carefully, as you may be able to avoid many regulations by simply settling for a small greenhouse.

Site. Your greenhouse site must have adequate light — six hours of uninterrupted sun on a clear day. You may have to trim or remove a tree to create more light for your chosen location. Also, consider access to water. Is there a nearby hose bib to provide water, even in winter? Some gardeners add gutters and an interior rain barrel to their backyard greenhouses for a winter water source. Electricity can power heating, lighting and ventilation, so keep an accessible power source in mind, too.

Vendors. Check companies carefully — even a small greenhouse is a big investment, and you should feel comfortable with the supplier. Don’t be afraid to ask questions, such as:

• How long has the company been in business?
• How many kits has it sold?
• Does it manufacture the kits or simply resell them?
• How extensive is the warranty?
• What technical help can the company provide?
• How is the greenhouse shipped and packaged?
• What is the cost of shipping?

You might add other questions to this list. If you have minimal building experience, read a copy of the kit’s manual beforehand to make sure it’s understandable to you. If you’ll be building the kit on weekends, ask whether someone from the company will be available to answer questions on Saturdays and Sundays. You may want to see demonstration photos or videos of the kit’s construction before committing to buy. Tech support may be limited if greenhouse kits are not the company’s specialty but just one of many products it sells. 

Greenhouse Frames

Most home greenhouse kits have frames made of either wood or aluminum. Wood frames tend to be more aesthetically pleasing but are a bit more difficult to construct. Wood can twist and warp, and wooden greenhouses usually include more parts. Aluminum greenhouses can be fragile or sturdy, depending on the model and the quality. Aluminum lasts virtually forever and is basically maintenance-free. Although generally easier to construct, aluminum frames conduct heat and cold and are a little less energy-efficient than wood.

Using a hoop house frame is another option to explore. A hoop house is a type of greenhouse made from a series of pipe hoops covered with heavy plastic that’s stretched tight and fastened to baseboards. Hoop houses are simple structures to build, and they’re an inexpensive way to control the climate over large areas, but they aren’t as durable as most kit greenhouses.

Glazing Types for Your Greenhouse Kit

“Glazing” is the term for a greenhouse’s exterior covering, such as glass or plastic. There are many variables to consider when selecting the right glazing for your backyard greenhouse kit.

Polycarbonate glazing is the most common type and is sold as either a single corrugated sheet or a multilayered honeycomb panel. Among the multilayered options, twin-wall is frequently used, but triple-wall and five-layered honeycomb panels are also available. Multilayered honeycomb polycarbonate is available in thicknesses from 4 to 16 millimeters. The more layers, the more expensive the glazing — but multiple layers conserve energy better. Multilayer glazings also reduce daytime heat from the summer sun, buffering the interior temperature so you’ll have a greenhouse that’s cooler in summer and warmer in winter. This glazing may be problematic for gardeners in climates with cloudy winters, because multiple layers filter out more light.

Polycarbonate glazing is treated with an exterior coating to filter out ultraviolet light. Because the coating is only applied to one side of the panel, make sure the treated side is facing out during assembly.

Most polycarbonate glazing comes with a 10-year warranty. It’s a tough material that can resist rocks and hailstones — until it gets old. The sun will eventually win and the polycarbonate will have to be replaced.

Polycarbonate is lightweight, meaning the greenhouse frame doesn’t have to be as heavy-duty as with other glazings. Unlike many plastics, polycarbonate is fire-resistant. It is also easy to handle and cut. It does expand and contract with heat and cold, though, and small greenhouses made with this type of glazing need a special mounting bar that helps the structure adjust with temperature fluctuations. Polyethylene glazing is available as a sheet film, woven sheet plastic or honeycombed material. Woven polyethylene is stronger than film. Polyethylene sheets, whether woven or film, are available with varying warranties for up to five years — the more years, the higher the expense. Polyethylene is still cheaper than polycarbonate, but a single sheet (either film or woven) doesn’t have the insulating value of a multilayer product.

Honeycombed polyethylene, sold as “Solexx,” is a double-layered product that looks similar to polycarbonate but is cheaper and doesn’t transmit as much light. It has a limited 10-year warranty. It’s noticeably softer and less rigid than polycarbonate, and it’s harder to weatherize because the softer edges are more difficult to seal.

Glass has the longest life of all glazings, assuming it doesn’t meet a rock or large hailstone. Difficult to cut and heavier to handle than plastic glazings, glass requires the support of a beefy frame structure because of its weight. Glass is available as a single sheet, as well as double and triple layers with better insulating characteristics. Tempered or laminated glass provides increased strength — essential for overhead applications. The positive aspects of glass include that it’s not combustible, doesn’t scratch easily, and has a low expansion/contraction rate in extreme temperatures.

Window glass is commonly sold as “low-e” (low emissivity), which means it has a surface treatment for energy savings. Plants grow more slowly under low-e glass, so I prefer untreated glass for greenhouse kits. Clear glass creates sharp shadows and doesn’t diffuse much light, which is less optimal for growing plants. Plastics diffuse light better, but the clarity of glass is great if you want to admire the view from inside your backyard greenhouse.

Fiberglass is great for diffusing light, which increases photosynthesis in a greenhouse. Commonly found in many brands and grades, it’s available both corrugated and flat, but only in a single-layer thickness. For that reason, fiberglass is often used in combination with a low-cost, insulating inner layer of polyethylene. Some brands turn yellow more quickly than others do, so that the life span of fiberglass products can vary from three to 20 years. Be wary of fiberglass sold in lumberyards — trust only a written warranty. Fiberglass is relatively strong but can be bent around large-diameter curves, such as hoop house frames. It’s easy to cut and work with, but do wear gloves, because the fibers can irritate your skin. It is highly combustible and has a low expansion/contraction rate.

Greenhouse Kits That Can Weather Storms Consider the wind when building your own greenhouse from a kit. If you live in a windy area, this not only affects your choice of glazing, but also means you’ll need to take extra care in anchoring your greenhouse to a foundation.

Film glazings, such as polyethylenes, are susceptible to wind damage. Woven polyethylene is sturdier than film, but the best material to use in windy regions is a sheet-like rigid plastic, such as multilayered polycarbonate. Fiberglass is also ideal.

Hoop houses are the greenhouse type most susceptible to wind damage. To combat this, hoop house owners sometimes use a double-inflated polyethylene film. The polyethylene layers are inflated by a small squirrel-cage fan. The inflation produces wind resistance by keeping the glazing rigid. Unfortunately, the power can go out when winds are high. Having a backup power source for the little fan is a good idea, otherwise your hoop house could suffer massive damage in a windstorm.

Be sure to check a greenhouse kit’s snow-load rating if you live in a snowy climate. You may risk greenhouse collapse unless you operate a heater, which will melt snow buildup on the roof.

Fresh Air and Sound Footing

Doors and Vents. Long-lasting, solid doors are important. Hinged doors are of higher quality than sliding ones. Some doors have removable or sliding panels that function as vents.

Most new owners of home greenhouses don’t give enough thought to the importance of ventilation. Overheating can be a major problem, so be sure your greenhouse comes with both low and high vents. The best greenhouse kits include automatic vent openers that are powered solely by the interior temperature. In areas with warmer summers, you should also consider the addition of an electric exhaust fan controlled by a cooling thermostat. It should be placed on the side opposite the door.

Foundations. Most greenhouse kits do not include a foundation. Usually you don’t need much of one, because most manufacturers recommend using rot-resistant, treated timbers in lieu of a concrete or concrete-block foundation. I prefer not to set greenhouse kits on concrete slabs. I like an exposed dirt floor because this setup gives me the option of planting directly into the ground, and it allows excess water to drain into the soil when I’m watering flats of seedlings. If you prefer something more substantial, check your local zoning laws for specific requirements.

If you opt for a simple foundation on timbers, it may take a day or two to build. Producing a level and square foundation requires a lot of fine-tuning, but it’s essential for proper assembly of your greenhouse kit. If your foundation is skewed, nothing will fit right and you’ll be guaranteed headaches. Gardeners who live in places with severely cold winters should consider adding 2-inch-thick foam board placed vertically against the exterior of their foundations or timbers, 1 to 2 feet down into the ground. The foam board set into the soil prevents the conduction of cold into the interior soil through the ground by tapping into temperatures deeper in the soil (45 to 50 degrees Fahrenheit in winter). Even when it’s minus 20 degrees outdoors, the foam will insulate the soil inside your backyard greenhouse.

Ready to Commit

You’ve made a multitude of decisions about your greenhouse kit — site, frame, glazing and more — but you’re not quite finished. Here are a few more tips to consider before you buy and build your own greenhouse.

Make an Offer. Many greenhouse kit retailers have regular sales and may be willing to negotiate the final price, especially if you’re knowledgeable about the competition. Don’t just compare kit prices — also factor shipping costs into your negotiation.

Warranties. The longer the warranty, the better the kit. Check the fine print, because the frame and glazing may have separate warranties.

Custom-Sized Options. Manufacturers may allow customers to order custom-sized greenhouse kits. Most gardeners eventually wish for more space, so purchase the largest greenhouse you can afford for your yard and budget, staying within local regulations.

Delivery. If you live in an area with severe winters, be sure to have the kit delivered during a warm season. Having the company store it for you is better than stashing it outside next to your garage. Wood-frame kits may warp if stored outdoors too long.

Before You Build. Check the kit thoroughly for shipping damage before you begin construction. Set aside some time to study the directions. Many problems people encounter with greenhouse kits are a result of not following the written directions.

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Greenhouse Kit Suppliers

ACF Greenhouses
Buffalo Junction, Va.; 800-487-8502; kits, accessories and supplies

BC Greenhouse
Surrey, British Columbia; 888-391-4433; glass and polycarbonate kits

Charley’s Greenhouse
Mount Vernon, Wash.; 800-322-4707; large selection of kits and supplies

FarmTek
Dyersville, Iowa; 800-327-6835; kits, irrigation supplies, heaters and lighting

Exaco
Austin, Texas; 877-760-8500; wide range of designs and sizes from German and Belgian manufacturers

Growing Spaces
Pagosa Springs, Colo.; 800-753-9333; solar-heated dome greenhouses

Harvest Pathway
Amherst, N.H.; 603-325-1232; dome kits, film and DIY resources

Solar Gem
Tacoma, Wash.; 800-370-3459; one-piece fiberglass greenhouses

Solexx Greenhouses
Salem, Ore.; 877-476-5399; home greenhouses and cold frames with polyethylene glazing

Sunrise Domes
Glocester, R.I.; 401-965-0753; geodesic dome greenhouses

Building From Scratch

Check out these suppliers and resources if you’re building from the ground up.

Build It Solar
free online design guides and plans for small greenhouses you can build yourself

Building a Passive Solar Greenhouse
drawing and materials list for a DIY solar-heated greenhouse

Solar Components
Manchester, N.H.; 603-668-8186; glazing, heaters and thermal storage tubes

Sundance Supply
glazing systems and extensive how-to information

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Shane Smith is the author of Greenhouse Gardener’s Companion, which covers all aspects of growing food, flowers and herbs in home greenhouses. Smith is the founder and director of the Cheyenne Botanic Gardens in Cheyenne, Wyo. Browse his website Greenhouse Garden

Grow More Food in a Portable Greenhouse

This portable greenhouse design has door flaps you can open for ventilation on sunny winter days.


Photo By Barbara Damrosch

Cam is trying to extend his growing season with DIY greenhouse structures.

Many gardeners use cold frames and quick hoops for season extension, but just beyond these is a simple and super-productive option for the home gardener: a small, low-cost, portable greenhouse. We’ve found that you can build a 10-by-12-foot greenhouse for less than you’d spend on a store-bought 4-by-4-foot cold frame. Our goals in designing this movable greenhouse were that it be simple to build with off-the-shelf parts, easy to move, easy to anchor and inexpensive.
Even gardeners in moderate or warm climates can benefit from a greenhouse, which gives you much more variety in your winter fare, and also makes the experience of growing it more pleasant. A greenhouse furnishes a warm and sheltered spot for plants, but because you can stand up inside of it, it also shelters you.
Similar to a cold frame, a simple greenhouse captures the sun’s heat and eliminates the drying, chilling effects of wind. You don’t even need to heat your greenhouse in winter if you plant hardy crops that are most content growing in cool weather. Come spring, you’ll get in those early crops even sooner than normal and you’ll transplant your warm-weather tomatoes earlier in the year. Then, sit back to wait for extra-early ripening.

Constructing Your Portable Greenhouse

The ability to move a greenhouse from one place to another will ease the seasonal transition from winter to summer and back to winter for all of the crops covered by the greenhouse. You can leave it over summer crops, such as tomatoes, peppers and basil, to safeguard them from fall frosts and keep them producing longer. Then you can move the greenhouse to protect cold-hardy crops that you’ve planted nearby so you can enjoy them well into winter.
With a portable greenhouse, you get the positives of greenhouse growing — namely cold protection — while eliminating the negatives, such as the pest and disease buildup that can occur in soil that’s continuously covered. In addition, you increase the number of crops that can be sheltered by one greenhouse by covering plants only when they need protection.
All that’s required to make a greenhouse mobile is a slight modification to its construction. (Four Season Farm provides step-by-step building instructions in Building the Modular Movable Greenhouse.) Normally, the standard pipe-frame, plastic-covered greenhouses stand on a foundation of pipes driven into the ground. Ours is firmly attached to the ground when it’s in place, but it can be detached for moving and then anchored again in a new location.
A greenhouse large enough to make a significant contribution to supplying your family with homegrown food year-round should be at least 10 by 12 feet. Our basic DIY greenhouse is just that size, and builders can double or even triple the length by adding on modules of the same size.

The frame consists of three half-circles of metal pipe attached to structural cross-pieces. A 10-foot length of pipe bends easily into a quarter-circle, and two of them form a half-circle hoop. We bend them the same way we bend our quick hoops, but we use a bender designed for high tunnels instead of low ones. For pipe, we prefer the 10-foot-long and 1-inch-diameter pipes used for electrical conduit (called “1-inch EMT,” which stands for electrical metallic tubing).

For the foundation of the greenhouse, instead of inserting the bottom end of the hoops into larger-diameter pipes driven into the ground, as with standard hoop houses, we attach the bottom of the hoops perpendicularly to a length of 1-inch EMT lying horizontally on the ground. With this setup, all parts of the 10-by-12-foot greenhouse module are connected as a single unit rather than having each rib individually attached to its own ground post. The greenhouse is thus like a metal-pipe, plastic-covered bird cage that can be picked up and transported to wherever you want it.

When the portable greenhouse is in place, we attach it to anchors to hold it there (they’re easily unattached for moving). The corner anchors consist of four lengths of top-rail pipe, each 2½ feet long. One is driven into the ground at each corner of the greenhouse, and each is attached to a U-bolt that secures to the base connectors.

We keep the plastic cover in place with form-fitting plastic clips that hold well even in wind. All of this works smoothly and keeps the price low. The weight of the pipes, the connecting parts and the plastic for this portable greenhouse add up to about 100 pounds. Thus the “pick up and move” part is doable for two reasonably fit and able-bodied gardeners. The two of us have moved this greenhouse many times with no problems.

More on Successful Greenhouse Growing

If you build your own greenhouse, you’ll love its benefits in winter. Achieve the greatest winter gardening success by growing crops suited to chilly weather. Read Best Winter Crops and Cold-Hardy Varieties for advice.

Check out the article Try Quick Hoops — Easy-to-Make Mini-Greenhouses for another season-extension option designed by the authors.

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Barbara Damrosch and Eliot Coleman are two of the country’s foremost authorities on organic gardening and winter growing. This article was adapted from their latest book, The Four Season Farm Gardener’s Cookbook — a great resource brimming with growing advice and recipes for the vegetable enthusiast


Gardening guru Eliot Coleman asserts that “the basic cold frame is the most dependable, least exploited aid for the four-season harvest.” We couldn’t agree more. Last winter, my humble box built of 2-by-4s topped with an old shower door added a month to the front end of salad season, but the best part was being able to sow some of my spring seeds directly into the frame. This made more space available under lights indoors for tomatoes and other crops that don’t like chilly conditions, and eliminated the hassle and setbacks involved with hardening off seedlings and then transplanting them. Best of all, seedlings get a nice head start in real sun so they never get stretched out and leggy as they often do when started indoors. (Indoor grow lights are vastly less intense than real sunlight.)
What can you sow in a cold frame? In spring you get a boost with virtually any crop by sowing into frames. The list of “Top 12 Winter Cold Frame Crops” (below) can get you started, and as days get longer and warmer in spring you can try your hand at framing up peas, bulb onions, potatoes or even tomatoes. When a cold frame is no longer needed for a crop that is up and growing, simply move it to a new location and plant more seeds.
Traditionally, gardeners have used cold frames to harden off seedlings started indoors, and you should have a frame suited to this purpose. But one cold frame is not enough. In addition to direct seeding some vegetables right where they are to grow, you can use a cold frame to winter-sow onions, cabbage or other hardy crops that are easily lifted and transplanted into rows.
A cold frame can be a wood box with a recycled window (or shower door) top, a hay bale enclosure covered with plastic, or you might build one with bricks or concrete blocks and top it with translucent corrugated fiberglass (see “Anatomy of a Cold Frame,” below). Your frames need not be all alike, though having two of the same size makes it possible to stack them for added height. I like frames I can move around by myself without straining, so size and weight are important considerations. If you live north of Zone 6, you may want to create frames that are large enough to accommodate black, water-filled containers for solar heat storage, and insulate the sides by adding a snug berm of soil or mulch. In climates with chronic winter cloud cover, you can maximize available light by painting the interior walls of your frames bright white, or by covering them with heavy-duty aluminum foil.

How Cold Frames Work

Cold frames shelter plants from ice, snow and treacherous winter winds, and heat up the soil whenever the sun shines. The soil inside a frame will warm up much faster than open ground, and because seeds of many hardy vegetables can germinate in the 50 degree range, a three-day spell of mild weather often coaxes them to life. Weed seeds will germinate alongside the seeds you plant, but you will see far fewer weeds if you cover the soil’s surface with a 1-inch-deep blanket of potting soil (purchased or homemade). Be prepared to add water as needed to keep the soil from drying out.After seeds have begun to grow inside the frames, the plants are surprisingly cold tolerant. I have watched lettuce seedlings sail through 10-degree nights when the frame was covered with a thick polyester-filled blanket, and framed-up spinach never sulks no matter how cold it gets. Yet these and other winter-sown vegetables will complain if a frame is allowed to overheat, so it’s crucial that frames be opened to vent out excess heat. When in doubt, it is always better to vent than to risk frying your plants. If you can’t be around to open and close your frame and a warm sunny day is in the forecast, covering the top of a closed frame with a light-blocking blanket for a few days is your safest strategy. If blustery winds threaten to sabotage your venting plan, place a board over the box, between the frame and the top, to keep it from slamming shut. Or use hooks and eyes to fasten the open top to posts sunk into the ground alongside the frame.

Climate-controlled Frames

Any cold frame will harness solar energy for your plants’ benefit, and there are several low-tech ways to help your frames retain solar warmth. Black antifreeze containers, milk or kitty litter jugs painted flat black can be filled with water and tucked into the corners. Or you can cover the spaces between plants with flat stones painted black or “solar pillows” — used freezer bags painted black and filled with water. If you want to get more sophisticated, check into the Solar Pods and Solar Cones developed by New Hampshire gardeners Leandre and Gretchen Poisson. Described in detail in their book, Solar Gardening, and in Mother’s online Archive, the Poissons’ devices are probably the best you can build, if you can afford the materials. The superior performance of these garden appliances comes from the use of Sun-Lite flexible fiberglass, which costs about $80 for a 4-by-8-foot piece.
Historically, gardeners have used the warmth generated by rotting manure to turn cold frames into hot beds. To make a hot bed, dig a hole inside your frame at least 12 inches deep and fill it with fresh horse manure mixed with straw, and topped with 6 inches of soil. As the manure decomposes, it releases heat into the frame.
But you don’t have to have fresh manure to build a hot bed — or at least a warm one. For example, let’s say you want to winter-sow broccoli, spinach or another crop that needs abundant nutrients. If you dig out a bed and refill it halfway with compost mixed with the cheapest dry dog food you can find (a sure-fire compost activator), and then top it with 6 inches of soil, the compost will generate enough heat to keep the little plants from freezing and thawing quickly — if they freeze at all. In spring, when the plants’ roots find the buried treasure deepin the bed, you may be looking at the biggest, best plants you have ever grown.Another option is to use the warmth generated by rotting hay to heat your cold frame from the sides. If you have plenty of space available and you plan to mulch with hay or straw this season anyway, go ahead and get four bales and arrange them in a semicircle on ready-to-plant ground, with the open side facing south. Plant the middle, and then top the bales with a wide sheet of plastic stapled to two 2-by-4s; one board will lie atop the back bales, and the other will anchor the plastic to the ground in front. You can make a bigger hay bale haven by arranging seven or eight bales in a square, and topping the enclosure with an old window, glass door or piece of sheet vinyl or corrugated fiberglass. Or, make your bales go twice as far by breaking them in half and encircling your planting with half bales, set side by side with their cut sides out. Allow the broken bales to get nice and damp before you plant, and then cover the bed and bales with a large piece of plastic sheeting. As the wet hay decomposes, much of the heat it releases will stay inside the bed.
To prepare a hot bed, warm bed or solar-charged cold frame when the soil is frozen, simply place a closed frame over the spot for several days. Daytime heating will thaw the soil inside, an inch or two at a time.
Various types of cold frames are multiplying like rabbits in my garden. With the help of the frames, spring now comes to my garden at least six weeks ahead of schedule.

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Top 12 Winter Cold Frame Crops

These 12 vegetables are easy to grow when sown in cold frames in late winter.

• Arugula
• Broccoli
• Beets
• Cabbage
• Chard
• Chinese cabbage
• Green onion
• Kale
• Lettuce
• Mustard
• Radish
• Spinach

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Milk Jug Seed Starters

This simple technique was developed for seeds that need to spend a winter outside before they will germinate, but it’s also a great method to start garden seeds in late winter if you don’t have indoor lights or a cold frame.

1. Cut a gallon milk jug (or other large plastic container) in half horizontally, leaving one edge intact to use as a hinge. Discard the cap.
2. Punch several drainage holes in the bottom.
3. Fill the bottom with 3 inches of potting soil, moisten well and plant your seeds.
4. Fold down the top cover, and secure the cut seam with duct tape. Enclose the planted jug in a large clear or opaque plastic bag (such as a produce bag), held together at the top with a twist tie.
5. Place in a sunny, protected spot outdoors.
6. One week before transplanting, harden off seedlings by removing the bag and tape, and propping the jug open with clothespins.

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Anatomy of a Cold Frame

Site Surface: Frames work best if the top is angled slightly toward the winter sun. You can either cut slanted sides (see illustration, Image Gallery) or, as an alternative, mound soil as needed to make the back edge of the frame sit slightly higher than the front.Frame: Scrap wood or untreated 2-by-4 or 2-by-6 pine boards are fine, or you can upgrade to rot-resistant cedar, redwood or locust or composite plastic lumber. Other options include logs, baled hay or straw, bricks or concrete blocks.
Corners: If you only have a hand saw, a hammer and a screwdriver, you can build a sturdy box from 2-by-4s, a few screws and four steel corner brackets. Brackets come in different forms — some for inside the box and some for outside. The simplest (and cheapest) ones screw into the top of a frame that’s already been banged together with 3-inch box nails.
Covers: The best materials for topping cold frames are tempered glass patio doors or shower doors, which often are discarded when homes and apartments are remodeled. Heavy enough to resist strong winds, shatter-resistant tempered glass doors are better scavenger hunt treasures than standard storm windows or paned windows, which can be a safety hazard. Look in thrift stores (Habitat for Humanity often sells donated doors), or call people in home remodeling or salvage businesses. Look for doors that still have plenty of hardware attached, and leave the hardware intact as you scrub down your prize. Later, after you’ve built a frame, the existing hardware may prove handy as part of a nifty hinge or a ready-made handle. Tempered glass doors come in all sorts of weird sizes, so it’s best to secure a top first, and then tailor the frame to match its dimensions.
Use thick blankets, quilts or bedspreads to bring winter-sown frames through winter storms, or to block sun when you can’t be around to vent the frames. Snow makes a good insulating cover, too.

Hoop House Update

A while back I explained my plan to extend the garden’s growing season by building  domed covers over my raised bed garden boxes and planting cold-tolerant plants.  I thought I’ll let you know how that’s going and what I’ve learned from the experience.

Fresh Vegetables in January

I planted mesclun lettuce, leaf lettuce, carrots, onions, chard, spinach, garlic, and Brussels sprouts.  On a weekly basis I’ve been able to harvest the lettuces, carrots, onions.  Chard comes in a little more slowly.  The spinach is alive but pretty well stopped in its tracks as far as growth goes.  I think this is mostly due to a lack of sunshine; which I will discuss in a moment.

  I didn’t plant more than a couple of squares of each plant because I didn’t want to be inundated.  That need not have been a worry.  We get enough each weekend to make one good salad, which will provide dinner once and provide a side salad once or twice for lunch through the week.

 My herb bed is also doing well and we can clip rosemary and oregano as needed.  The sage has gone dormant, so I don’t take cuttings from that.  I moved a basil plant into my office and that serves our needs well since I have to clip it aggressively to keep it from bolting.  I’ll plant fresh seedlings in the herb bed in the spring.

What I’ve Learned

The biggest mistake I made was in planting beds that are in a shaded area during the winter because the sun sits lower in the sky in winter than it does in summer and trees along the edge of my property block the sun.  In the summer this was not a problem.  Next year I’ll need to put in more boxes and the winter garden will be higher up the slope where full sun is received most of the day.

This lack of sun is compounded by the fact that the plastic covering the houses is semi-transparent, so it may be blocking some of the sun.  Whenever possible I go out and pull the covers off the beds on warm sunny days.

I was afraid that watering the beds would become a chore since I had to disconnect and drain the water hose for the winter.  But this has not been a problem.  Rain that falls on the cover slides down the sides and into the edges of the box.  The vermiculite in the mix then helps hold the water for the plants.  And because there are not many warm, sunny days where I pull the covers, the moisture that gets inside tends to stay there.  Evaporated moisture condenses on the inside of the cover and falls back to the soil as it gathers into droplets.  I have not had to add water even once so far.

One thing I did think to do was to make slits on the plastic where it wraps around the lower side bars.  This allows the water that runs down the sides to escape and fall back into the soil instead of building up in the pocket this wrapped plastic forms.

I have learned that there are some PVC pipe fittings that would allow me to build a “house” shaped roof rather than bending the piped into a hoop.  The hoop puts a lot of tension into the system and this can cause some problems with joints popping loose and legs not wanting to fit into their sockets.  Building domes with short straight sides and a peaked roof would take all the tension out of the system.

Conclusion

I’d say the project is a success; it is providing us with fresh food and will have a great start on the early spring crop because much of it is already in the ground.  I need to be more mindful of the suns winter position and put out more plants next year.  But it has worked well.