The Winter Harvest Handbook

It is common sense to take a method and try it. If it fails, admit it frankly and try another. But above all, try something.

Like most fresh-vegetable enthusiasts, I have always wanted the production season to be never ending. That doesn’t mean I long for an endless summer. I love the pleasures of fall, winter, and spring. I just want year-round freshly harvested food for my own and my customers’ tables. I always knew that, somehow, there had to be a simple way to combine cold-hardy crops with a little protection during the cold seasons so I could produce food economically throughout the year even in the New England climate.

Cold frames have always been the simplest and least expensive climate moderator for the gardener of limited resources. I began using cold frames when I started as a grower in 1966, but I first started seriously developing these winter-harvest ideas from 1978 to 1981 when I ran an organic experimental farm just north of Boston, Massachusetts. I refined the system from 1982 through 1990 on a farm in a very cold area of Vermont. The fact that they worked just as well in those two different climates as well as subsequently here on the Maine coast convinced me of the wide applicability of winter production.

During the early years of my interest in the Dutch cold-frame design known as “Dutch lights,” the following books were helpful:

Carter, A. R. Dutch Lights for Growers and Gardeners. London: Vinton & Co., 1956.

Quarrell, C. P. Intensive Salad Production. London: Crosby Lockwood, 1938.

Willmott, P. K. Dutch Lights and Frames. London: Ernest Benn Ltd, 1958.

On trips to European farms during the 1970s, I had visited the few remaining practitioners of commercial cold-frame production of hardy winter vegetables in Holland as well as France. Their simple cold frames fascinated me because they did not employ highly technological solutions. To me, Styrofoam insulation, awkward reflective covers, and space-age materials seem inelegant. I am convinced that simpler is better, especially where simpler has been time-tested. Comparative investigations of different cold-frame designs show that the standard old-time model—a bottomless box made of 2-inch-thick planks, 8 to 12 inches high at the back and 6 to 8 inches high at the front, and covered with glass panels—is still the best. So I copied the Dutch design—approximately 30-by-60-inch glass panes in a wooden frame, (known as “Dutch lights”)—because they were simpler to make than the French models I had seen at Savier’s market garden.

Those simple glass panes over bottomless boxes gave our plants a surprising amount of protection. Growing plants in a cold frame is the equivalent of moving them to a climate one and one-half USDA zones warmer, or about 500 miles to the south here on the East Coast. A cold frame will usually prevent the crops inside from freezing until the outdoor temperature goes below 25°F. But our winters get a lot colder than that, so in the winter of 1980, we used our imagination and took a chance. We had an unheated greenhouse constructed in a traditional Dutch style—a structural frame consisting of 2×4s and covered with the Dutch lights. We planted it with winter crops and erected cold frames inside over the crops. Voila! The great leap forward! Our plants moved an additional 500 miles to the south to a Zone 8 climate and, as icing on the cake, had a snow-shedding roof over them.

It is fascinating how one step forward will suddenly help focus your thinking about an overall concept. This was one of those moments. First, the simplicity of adding a second layer made me understand better what we were achieving. We were not actively battling against the cold of winter, as one is doing when trying to grow hot-weather crops in a heated greenhouse. Rather we were simply maintaining a protected microclimate sufficient for the needs of our hardy plants. It was like the difference between sitting inside by the fire on a cold day and being outside with enough layers of clothes on to keep you comfortable.

Second, we began to pay attention to how plant growth changed as the season progressed. Once past the middle of November, most of the crops no longer grew at summer speed. They were semi-hibernating, just idling their engines, so to speak, waiting for us to come and harvest them. In other words, we were not extending the growing season as one hopes to do in a heated greenhouse but, rather, we were extending the harvest season.

Those realizations really helped us turn the corner on developing this concept of winter vegetables in protected microclimates. Lacking a guide, at first we had to guess at when to plant. During our first few winters of experimentation, it was obvious that some of our crops were too small to be harvestable while others were too large to be as hardy as they ought to be to survive the winter days yet to come. (Younger plants are usually hardier than older ones.) We hadn’t done too badly, but a lot more experimentation was necessary in future years in order to arrive at the ideal August, September, and October planting dates that would result in a productive winter harvest. Furthermore, we could tell that some of the crops would benefit from two, three, and even more successive planting dates so as to spread out the harvest better, and to take advantage of what slow growth did take place between mid-November and early February. Succession planting ensured that we would have more to harvest once the new year got well underway.

From that early beginning, the winter-harvest concept has blossomed. A few years experience gave us more precise knowledge about planting dates and determining when to add the inner layer. In addition, we experimented with making greenhouses movable. We devised basic systems for sliding hoop houses between two alternate sites. The first design relied on greased wooden skids sliding on wooden rails; another called for rails on the bottom of the structure, which rolled along on ball casters set in the top of support posts; a third had runners that slid directly along the ground like a sled; and a fourth had flanged wheels on the bottom of each hoop that rolled along pipes lying on the ground. (More on this in chapter 10.)

Up until the early 1990s, when we decided to pursue this idea on a serious commercial basis, our inner layer was the cold frames with which we had begun. However, we realized that in order to grow winter crops commercially, we had to find an inner layer that was less expensive and more time-efficient. (Cold frames are costly to build and need to be manually vented so they won’t overheat on sunny days.) After a winter of trials, we could easily see that the obvious choice to replace the glass was floating row cover held a foot above the soil on flat-topped wire wickets. Although row covers did not provide quite as much climatic protection as the cold frames had provided, row covers were self-venting, lighter in weight, easier to place over or take off the crops, and much less expensive.

Similarly, we knew we should shift production to larger greenhouses than our early prototypes, and we decided upon 30-foot-wide-by-96-foot-long houses as the most efficient choice. We had never moved greenhouses that large before, but by using our metal sled-runner design, and pulling them with a tractor just as one would pull a large sled, we had greenhouses that moved reasonably easily and could be bolted securely to ground anchors once they were in place.

At the start of our foray into winter production we joked about how it might be possible to run a “backwards farm,” producing salads and main-course vegetables from October 1 to May 31, and then taking a long summer vacation. So, for a number of years, we tried winter-only growing. We were curious to learn what was possible if we concentrated all our energies on the unexplored potential of winter. The reality was not quite as good as the dream. There was indeed a whole new eight-month harvest season, but vacation time was limited to the second half of June (after cleaning out the greenhouses) and the first half of July (after which the work of preparing everything for the season to come actually begins).

We grew green manures during the summer season to boost the soil up to high production standards. We also worked on refining many of the unique greenhouse design and cropping programs that I present in this book. Our present year-round schedule is the result of combining all we have learned from summer-only and winter-only growing into a system that supplies the best of both. In chapter 4, I’ll explain all the details about how our schedule ebbs and flows throughout the year.

Another dimension of the winter harvest is the quality that it offers to our customers. Their appreciation is the most gratifying we have known in many years as professional growers. People love having access to food harvested fresh either that day or the day before on a local farm—in the middle of winter! Over the past few years a flurry of articles have appeared in newspapers and scientific journals confirming what everyone’s mom always knew: “Vegetables are good for you!” Government nutritional recommendations exhort us to eat five servings of fruits and vegetables daily. Customers tell us that our winter-harvest products make it easy for them to eat vegetables.

• First, the taste, the sweetness, and the just-harvested freshness are exceptional. Their children ask them for our raw carrots. One woman told us that she used to suffer all through the winter looking forward to fresh summer vegetables. Now, she said, she tolerates summer looking forward to eight months of intensely flavorful winter production.

• Second is convenience. Our salad mix has been referred to as a healthy fast food, “because it looks so inviting you want to eat it, and is so easy to put a handful into a bowl and add dressing that you do just that.”

• And third is the fact that it is grown locally during the winter months. Customers say winter doesn’t seem so long or bleak when they can always look forward to our next locally grown delight.

For our part, we can now participate in all the seasons of Nature’s cycle, and we enjoy farming as an ongoing process, not just the start-and-stop operation it was when we were only summer growers. And remember, this is happening in Maine. Over 85 percent of the U.S. is further south than where we are and has more sun and warmer winter weather. There’s nothing standing in the way of winter production of high-quality fresh produce in any part of the country, except perhaps lack of knowledge about how to employ the simple technology of cold houses and row covers and lack of experience in planning planting schedules for continuous production.