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Grow more food in a movable greenhouse: boost productivity in spring, summer, fall and winter with a do-it-yourself greenhouse you can transport around your plot.

Many gardeners use cold frames and quick hoops to extend the growing season, but just beyond these options is a step we think is simple and super-productive for the home gardener: a small, low-cost, portable greenhouse. At first this may seem like a big step. We've found, however, 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, wherever you live, and also makes the experience of growing it more pleasant. Like the cold frame and the quick hoop, a greenhouse furnishes a warm and sheltered spot for plants, but because you can stand up inside of it, it also shelters you. Just think about heading out with your harvest basket in hand, even while there's fresh snow falling.

Similar to a cold frame, a simple greenhouse captures the sun's heat and eliminates the drying, chilling effects of wind. Often a gardener's first thought will be: "Wouldn't it be nice to grow warm-weather crops, such as tomatoes, during winter?" But that would mean providing some sort of artificial heat, and suddenly the simple greenhouse becomes a big expense. Here's the great part: You don't 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--all of this with no artificial heating required!

The Greenhouse Structure

The frame of a non-glass greenhouse--the structural surface against which the plastic covering rests--can be made of a far wider range of materials than the frame of a glass greenhouse can be. We've seen them made of bowed saplings from the woods or curved sections of concrete-reinforcing wire panels. We've seen greenhouses made with a few leaning poles holding the plastic sheet out from the south wall of a building. All of these simple structures shelter plants well and show the creativity gardeners employ to be able to grow food all year.

In the standard commercial greenhouse, bowed metal hoops forming a pipe frame support the plastic sheet. This is what the phrase "hoop house" describes, and it's the style on which we modeled our greenhouse. But we've added a trick to make it even more productive: It moves!

The Movable 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. Such crops don't mind early frosts--in fact, they prefer to grow in the increasingly cool days of fall.

If a greenhouse can be moved to where you want it, when you want it, a whole new world opens up. 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. Normally, the standard pipe-frame, plastic-covered greenhouses stand on a foundation of pipes driven into the ground. The far more expensive glass ones are usually erected on a concrete foundation. 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 greenhouse is just that size, and builders can double or even triple the length by adding on modules of the same size. (For detailed building instructions, go to 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 (find hoop-bending forms through Johnny's Selected Seeds; 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). They are available in the electrical department of your local home-improvement store.

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 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 2 1/2 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, and because the greenhouse isn't so heavy that it has to be dragged into place, you can put it on any site, no matter how distant from the greenhouse's original position. If that seems beyond you, find some extra helpers on moving day.

Ideas for Every Season

This greenhouse design accommodates plants grown directly in the ground--not plants cultivated on the waist-high benches some hobby greenhouses feature.

The winter inhabitants of your greenhouse will be cold-hardy crops. Plenty of vegetables can withstand cold weather, and some actually taste better because of it. A few frosts have a way of sweetening leaf crops and root crops. Over the years, we've experimented with some 30 different vegetables in our winter garden, including arugula, beet greens, carrots, chard, chicory, claytonia, collards, kale, kohlrabi, leeks, lettuce, matche, mizuna, mustard greens, parsley, radicchio, radish, scallions, sorrel, spinach, tatsoi and turnips. (For specific variety recommendations for several of these crops, go to They've all been successful to some degree, and the favorites in our household are spinach, carrots, tatsoi, chard and kale.

In most of the country, these crops are harvestable through winter as long as they have the minimum amount of protection from the outdoor weather that a single layer of plastic can give them. Here in Maine, we usually move the greenhouse over the winter crops about mid-October and plan to start eating those crops about mid-November.

In a very cold climate such as ours, a second layer of protection inside the greenhouse will increase the value. We've kept temperature records for years, and here on the Maine coast, our portable greenhouse alone creates a winter climate akin to that of New Jersey, and the second inner layer magically transports the area under it to Georgia. When it's 15 below zero outside in Maine, it's 18 degrees Fahrenheit under the greenhouse's inner layer, and the cold-hardy winter crops don't mind that at all.

Your greenhouse can also help you transition from winter to spring. After our winter spinach begins to go to seed in spring, for example, we can clear the bed, add more compost, and replant it with early tomatoes. Thus, tomatoes get going about six weeks before our last spring frost date, because the double-layer of protection will keep them from freezing.

Our summer crops will have a great head start, and in this temperate climate, they will keep producing all summer as long as the greenhouse is well-vented. The doors at either end--we call them "scissor doors"--are used for both access and ventilation, and they allow for complete air flow if tied in the fully open position. If you live where summers get quite hot--too hot for even a well-vented greenhouse--you have other options. For one, you can uncover the greenhouse by taking off the plastic after it has given the early crops a jump-start, but before they're going to bake in there. If you prefer to leave the greenhouse covered, you can add a layer of shade cloth over the plastic to decrease the heat buildup. A 40-percent shade cloth made of a reflective material is a good bet for the backyard greenhouse. Or, you can always move the greenhouse out of the garden for a few weeks, until you're ready to put it to use again.

If you'd rather have more instant gratification in spring from salad-type vegetables than wait for tomatoes, peppers and the like to mature, another winter-into-spring planting scheme could be the following: Plant patches of beets, carrots and spinach along with a bed of potatoes (early baby new potatoes are a fine greenhouse treat). Plant lettuce along with a few scallions at one end. The beets, carrots, lettuce, scallions and spinach can be planted anytime in spring as soon as the space can be cleared from your winter crops. We plant our early potatoes on March 15; 'Rose Gold' is our favorite variety for early greenhouse production. Of course, you could always have all of these in addition to the early tomatoes, etc., if you built a second greenhouse. We're betting you probably will.

Another summer option for your greenhouse is to trap heat and use that heat to your advantage to prevent future weeds and pests in a process called "solarization." To do so, clean out all the early greenhouse crops after the outdoor garden starts producing. Irrigate the greenhouse thoroughly, lay a sheet of clear plastic over the soil inside, and shut the doors. Those two layers of plastic (the greenhouse itself and the plastic over the soil) will trap enough of the summer sun's heat to kill weed seeds and plant disease organisms down to at least 4 inches deep in the soil.

To get step-by-step instructions for building this portable greenhouse, go to Although we've been using these techniques for 30 years, the thrill has not worn off. We're still as delighted as children by the wide range of crops we can harvest daily from our greenhouse garden.

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. See Page 64 to order this resource brimming with growing advice and recipes for the vegetable enthusiast.
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Author:Damrosch, Barbara; Coleman, Eliot
Publication:Mother Earth News
Geographic Code:1USA
Date:Dec 1, 2013
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