The frame of a greenhouse built to hold rows of vegetables to last through each season.
Written By Anne Raver
Sooner or later, any gardener who gets hooked on arugula and tangy greens or a mess of tender spinach just picked from the garden starts extending the season at both ends.
First, you may find yourself bundled up in a parka, planting seeds of winter purslane or miner’s lettuce (Claytonia perfoliata), so-called because miners of the California Gold Rush stopped pounding rocks long enough to pick and eat the leaves of this hardy wild green, which is high in vitamin C and helped prevent scurvy.
I used to scatter seeds of it on the south side of the house during a February thaw. I also plant spinach seeds in August, so they take root and start producing leaves long before frost. Then I cover them with spun polyester cloth, like Reemay, or Agribon, laid over curved metal rods; and voila, a low hoophouse! If temperatures drop below 20 degrees, I add another layer of plastic, which literally gives double protection. And we eat spinach most of the winter. The leaves stop producing during the lowest light in January, then pick up again as the light grows stronger in February.
My kale and Brussels sprouts need no such protection, especially in a warm winter, and actually taste sweeter as temperatures drop.
I also use a cold frame or two, planted with hardy greens, including arugula, mache and bok choy, to produce more leafy vegetables during the cold months.
A cold frame is basically a bottomless box with a slanting clear lid, made of glass or plastic, set to face south for the most solar gain. And to my mind, it is the best solution for a gardener who does not want to spend a lot of time building a greenhouse, or a lot of money for a ready-made one. (My husband, Rock, and I built a greenhouse with friends, a few years ago, for better or for worse.)
Even with the greenhouse, we still feast on greens from two cold frames.
The first was built years ago with thick cedar boards: the back board is 12 inches high, the south-facing front board, 8 inches high; the two side boards are cut on a diagonal and an old storm window serves as the lid. (There are many instructions, including You Tube videos, for cold frames on the Internet.)
Our more recent cold frame is even more rustic, with its hay bales and boards that still have bark on one side. These came from a black locust tree felled in our backyard by a violent storm and milled by a man right on site.
Black locust was long used by settlers for fence posts, because it is so rot-resistant, and we actually used the best boards to replace the old floor of our kitchen porch. The wood is great for anything in the garden, because it does not have to be treated with toxic chemicals, like creosote, to repel water.
As for our cold frame, we used hay bales to form the sides and to insulate the north end. Yet another storm window completed the job.
The only problem with these simple cold frames is that they can over heat, even on a freezing day, if the sun is out. So you have to vent them with a little stick. If I am going away for the day, I do this early in the morning, even if the sun is not up, and have never had a problem with frozen plants.
And do not forget to water those greens: They can heat up and dry out.
If you are not the handy type, can buy a fairly good cold frame for a reasonable price. I had a Juwel cold frame that worked well for years; it sells now for about $130 (www.groworganic.com). You can buy them with automatic vent openers, or for that matter, buy an opener to attach to your homemade frame.
These simple hoop houses and cold frames work beautifully with a fraction of the trouble and expense of a greenhouse. But I only say that with the clarity of hindsight. I was overcome with envy one day a few years ago, while basking in the tropical warmth and fragrant Meyer lemon and grapefruit trees blooming one February day at a greenhouse built by our friend, Ed, who happens to be a farmer and nurseryman with all the tools and ingenuity of his farming ancestors.
He heats his office and four greenhouses by burning recycled vegetable oil; solar panels on the roof help heat water pipes running under the floor of the greenhouse I fell for, which is laid with brick and feels like some kind of Mediterranean paradise. It also had a deep in-ground planting bed for lettuces and cherry tomatoes. I was hooked.
After Ed offered to help us build something similar (without the solar panels and radiant heat beneath the floor), we put up a half-hoop house, with curving metal bows and big sheets of flexible double-walled plastic, attached to the south wall of an old shed. The concept was good, but our version left a lot to be desired. We have a lot of air leaks, automatic vents that refused to open, and rather costly propane gas bills, because we decided to install a space warm enough for citrus plants and overwintering my bougainvilleas, fragrant geraniums and African lilies.
We have had a lot of fun with it, though, and I suppose the whole thing is cheaper than a week in Key West. It really is a pleasure to enter this space on a wintry day, and we have to peel off two sweaters to get comfortable. I keep an old chair in there, for comfortable reading and writing, and there is something wonderful about being out in the garden with the cardinals and snow, with some protection overhead.
As for its horticultural benefits, my rosemary and basil continue to produce all winter, rather than dying slow deaths in the windowsill. And Rock built a beautiful deep bed – about 8 by 4 feet, and 12 inches deep – right on the old concrete floor of our shed-turned-greenhouse. So I grow a lot of spinach and mesclun there, as well.
We also use the space to start seeds, and they grow beautifully in the natural light. Our homemade rain barrel, fashioned from a 55-gallon, industrial-sized container, collects water off the roof. Painted black and set about four feet off the ground, it provides us with gravity-fed water all winter.
Considering the high cost of fuel, and our desire to conserve resources, we probably will not heat the greenhouse next year. But we will grow plenty of greens in Rock’s raised bed, under a plastic cover, which will give the plants double protection in the greenhouse.
I have seen this work beautifully at Four Season Farm, owned by Eliot Coleman and Barbara Damrosch in Harborside, Maine. In fact, these two long-time gardeners have tried almost every cold frame and hoop house, including ones that move on runners, under the sun. And they have an elegant glass one attached to their house. The beauty of a movable greenhouse is that you can plant crops in the fall, then move the greenhouse over them for winter protection. Conversely, in spring, you can start seeds early in the greenhouse, then move it off the beds when it is warm enough for them to flourish outside.
With all that Rock and I learned from our ups and downs with greenhouses, I’d be inclined to buy a movable one that attaches to the house – if I win the lottery.
The Coleman and Damrosch’s recent book, The Four Season Farm Gardener’s Cookbook (Workman, $22.95), published last year, is a compendium of how to grow and preserve, as well as cook, delicious fresh food year-round at home, even in a small space. The book includes instructions for cold frames, hoop houses and movable greenhouses, as well as resources for buying them. Four Season Tools, a company in Kansas City, Missouri, for example, custom-builds Coleman-style hoop greenhouses (www.fourseasontools.com; 816-444-7330).