Cold Frames

Gardening with cold frames at Light Morning

With May now under way, the season for cold frame gardening is drawing to a close. I keep my peppers and tomatoes warm on colder nights by closing the glass, but more often than not the glass stays completely off to allow unexpected thunderstorms to water the plants. More and more, the frames start getting in the way, though they are still very much appreciated when the threat of frost is issued on the radio.

By the middle of the month I am eager to get the cold frames off of my solanums and onto my cucurbits. I find that winter squash and melons especially enjoy the extra heat for germination and good growth until June’s blazing temperatures make the cold frames altogether superfluous. In spite of the cold frame, I will still put some hooped row covers over the young plants to slow down the squash bugs and cucumber beetles. It is nice to have the boxes hide the otherwise unsightly white gashes in the landscape.

By the end of May it is time to really start finding an out-of-the-way home for my cold frames. Not too out of the way, however, since I have found that cold frames make suitable solar dryers for fruits and vegetables. Sliced tomatoes, laid on screens, will dry in two or three sunny days! The heat trapped by the glass pumps the moisture right out of the vented crack I leave at the top. The glass also acts as a convenient barrier to rain and dew; no need to ever transfer the drying racks indoors.

This year I may even try curing my onions and garlic in the cold frames. It will probably be necessary to find something to shade the bulbs from direct sunlight. With careful monitoring, I hope that the cold frame might simulate the conditions of the awkward-to-reach attic where I usually cure my alliums.

Last year I tried to cure our sweet potatoes in the cold frames (they need warm humid conditions to encourage sweetening and storability) and had moderate success. I may have removed them from the frames a little too early, however, for the tubers never got their full flavor.

Before concluding this series of articles on spring cold frame gardening, I will share my revised timeline for next year’s sowings and plantings as a brief review and reference guide.

January (early)–Start Crucifers (Broccoli, Cauliflower, Cabbage)and lettuce seedlings. / Sow Salad Greens direct in cold frames.

January (middle)–Start Solanums (Peppers and Tomatoes) & Basil.

February (early)–Prick out Crucifers into small pots and put in an insulated seedling cold frame. / Sow Peas and root crops direct in cold frames.

February (middle)–Prick out Solanums into small pots.

February (late)–Re-pot Crucifers into larger pots.

March (middle)–Plant out Crucifers into cold frames. / Re-pot Solanums into larger pots.

March (late)–Sow Cucumbers and Summer Squash in large pots.

April (middle)–Plant out Solanums, Cucumbers and Summer Squash into cold frames. / Sow Melons and Winter Squash in large pots.

May (early)–Plant out Melons and Winter Squash into cold frames. / Sow more Melons and Winter Squash direct in cold frames.

Similar magic can be had by extending the season for fall crops with cold frames. This makes year-round gardening possible in our county. Quite the trick, especially if you can manage to do so without burning out!

By starting a late crop of tomatoes in June, I am able to get fruits to mature in cold frames in October and November. Special keeping varieties, like Burpee’s “Longkeeper,” will continue to ripen in storage well into January. A well-timed crop of lettuce will head up and be protected from the first heavy frosts of October and November, while baby salad greens can be direct seeded almost anytime, sometimes surviving even the coldest nights of winter.

Another nice addition to the winter cold frame garden is cooking greens like kale and spinach. These will provide infrequent meals throughout the winter and will then produce abundantly in March and April when warmer weather arrives. This past winter I learned that beets make a hardier substitute for chard in the cold frame. They are really the same vegetable, genetically, with the added bonus of having their roots, as well as their tops, be edible!

I hope that you have enjoyed and will benefit from the information shared in these articles, and that someday you will share with me your own cold frame experiences and discoveries.

Happy Gardening!

Jonathan weeding cold frame

Jonathan weeding cold frame

April is a busy and exciting time, especially when gardening with cold frames. While convincing signs of spring are just beginning to emerge outdoors, summer is well under way under the glass. With temperatures consistently 70° or above by day, and the danger of frost essentially gone, almost anything can be grown in the frames by mid April.

By early April, my broccoli and cauliflower plants will be pushing against the glass, exposing them to frost and sunburn. To avoid this, I have built extension boxes that essentially raise the height of my cold frames. By the middle of April, those plants are getting little benefit from the extra heat and protection of the cold frames and I carefully find the proper timing to remove the frames and let the young plants fend for themselves.

I eagerly look forward to the day when I plant out my tomatoes, peppers, and basil into the freed-up cold frames from my liberated crucifers. I again aim for the middle of a warm spell. Started in January, the tomatoes are usually bursting out of their pots, some of them with flowers blooming.

I will plant those tomatoes as deep as I can to encourage extra rooting from the stem, making sure to leave the flowers above ground for the possibility of some early fruits in May. Since determinate varieties of tomatoes have a bushing habit and do not vine like their indeterminate cousins, my cold frame plants don’t need trellising. However, the plants do have a tendency to flop over, so to prevent the fruit rot this encourages I have learned to put a hoop tunnel made from fencing for the plants to grow through, giving extra support for the luscious, pendant fruits.

This year I am growing twice as many cold frame peppers as last year. If you have ever struggled, as I have, with getting peppers to flower and fruit in the summer, cold frames may be your solution. I probably got more fruit, in one quarter the area, from my cold frame peppers than I did from the main-crop plants I started outdoors, all due to one month of extra, early protection.

The early-started plants, moreover, were spread out through the whole season and had plenty of time and fruit for early red peppers, unlike the regular plants that were mostly foliage all summer, with an excess of unripe fruits just before frost. Once again, a good example of how concentrated energy and attention can pay for itself multifold!

If you don’t have early tomatoes or peppers to plant, don’t fret. It is still not too late to start some fast-growing cucumbers and summer squash in pots to be planted out later this month. Kept in a warm, bright location, the large seeds will germinate quickly and will need to be planted out into cold frames before the roots crowd the pot, since cucurbits are not that fond of being transplanted in the first place. In fact, by mid April you could even direct seed those plants right into a free cold frame if you prefer.

Being such powerful tools of growth and transformation, cold frames do not come without certain costs and dangers. They will need constant monitoring, especially at first while getting the hang of it. Expect to learn the hard way, since all it takes is a couple of hours of midday sun without venting to find the foliage of your tender plants burnt to a crisp. Transpiration is also extreme in the greenhouse environment, so frequent watering is necessary. Opening the cold frames completely for soaking rains is ideal.

If you do find your plants burnt or withering, don’t give up. I have been amazed at how quickly well-rooted plants (much like their human counterparts) can regenerate themselves. Nevertheless, I hang onto any extra seedlings I have, in order to fill in holes caused by pests or problems. There is nothing more satisfying than a full house of plants.

It is also helpful to have family, friends, and neighbors who are supportive of your cold frame initiative. Otherwise, being tied down to cold frame maintenance will start feeling like a confining chore and not like the labor of love it was meant to be. Those early cauliflowers and tomatoes make flavorful rewards and compensation for the hard work of yourself and others.

Moreover, any mistakes and shortcomings will ripen into lessons for next year’s experiments. Already this year I have regretted my early broccoli transplant that left my tender kale and chard unsheltered. Shocked by a sudden drop in nighttime temperature, they lost most of their foliage to frost and windburn and have taken three weeks to recover. In the May article, I will share my revised timeline for next year’s sowings and plantings. Until then, happy gardening!

Jonathan moving cold frame

Jonathan moving cold frame

As the spring equinox draws near, the cold frame gardener finds it easy to stay busy. With greens, peas, and root crops already sprouted, it is a good time to look for holes in the rows of plants (often due to rodents) to re-sow. Be sure to keep the frames vented on sunny days and well watered. You can even remove the glazing entirely to catch any warm spring rains.

Now that your confidence in cold frames is swelling, you can begin to focus on your transplant seedlings. Assuming that you have already started your broccoli, lettuce, tomatoes, and other such delights, it is important to get these seedlings into containers in order to sustain the seedlings until transplant time. I tend to be short on space and will use small, 2 1/2″ pots with the option of re-potting into larger ones as needed. Though this is more work, I find it easier to keep a smaller area well protected and watered when the weather outdoors is still harsh.

Most seedlings need to be pricked out into pots about two weeks after germination, once true leaves have emerged and before the seedlings get too crowded and leggy. If (like me) you are without a greenhouse, your potted seedlings can get by with a cold frame that is well insulated with straw or leaves. A blanket and tarp also help reduce heat loss through the glazing on cold nights.

It is important to keep a watchful eye on the seedlings after they have been transplanted (bare rooted) into pots. Shading from direct sunlight is often necessary for the first few days. Lacking the buffer of a large soil mass, potted seedlings tend to be even more sensitive to extremes. Venting the cold frame is often necessary by mid-morning on sunny days in the 50′s. And all it takes is one frozen night to permanently shock a potted seedling’s root system.

Caring for seedlings in a cold frame in March is a delicate and demanding art. Guided only by a thermometer, observation, and intuition, the dedicated gardener must ensure that the seedlings survive and ultimately thrive through the extremes of temperamental Spring weather.

Why does the eager cold frame gardener bother to take on such a challenging task? Of course, there is the obvious explanation of early produce. What a shame to wait until July or even August for tomatoes when June and often May are already sunny and hot.

Another reason for all the labor that goes into extending the growing season is that it reduces the need for labor- intensive food preserving. Since the quality and nutritional value of fresh produce is incomparable, the cold frame gardener is doubly rewarded.

Moreover, cold frames reduce the temptation to purchase non-local produce whose real environmental cost is hidden. And any surplus from the cold frames can be bartered or sold to neighbors for a premium.

But there are other, less tangible benefits as well. I have found plants to be good reflections of our spiritual selves, with many parallels between caring for early seedlings and caring for one’s soul. Living in the somewhat protective environment of this community and this county, I often feel like a sheltered seedling. The warmth coaxes me to grow and evolve, but there is also the risk of being blasted by extreme conditions or negligent care. Like seedlings, we must trust in the coming season. When we are transplanted into the garden, and our roots are finally free to stretch deep into the Earth, our ripening fruit shall serve as signs of what is possible for the human species.

So by mid to late March you can begin to think about transplanting your hardier plants into cold frame protected garden soil where they ultimately belong. One of the main benefits of having individually potted seedlings is that there is virtually no transplant shock. Nevertheless, it is helpful to time the transplant during a period of mild weather and to warm the soil by moving the cold frames into place a few days prior to transplanting. You should hopefully be able to safely steal cold frames from the peas, root crops, and greens that you sowed last month.

Because my cold frames are precious real estate, I tend to pack them with plants that use extra compost and premium garden soil. When transplanting, I will crowd broccoli and cauliflower in staggered rows with 15″ spacing, even squeezing in some quick-growing lettuce in spare corners, to be harvested before their larger neighbors take over.

Less hardier crops like tomatoes, peppers, and basil will need to remain potted a month longer, until the cold frame housing your broccoli and lettuce frees up in April. The tomatoes especially may need quart-size pots before long to tide them over until then. More on the care of these warm weather crops and the maturing plants in your cold frames next month.

Jonathan watering coldframes

Jonathan watering coldframes

For several years now I have been experimenting with growing seedlings and plants in cold frames at Light Morning. The successes never cease to amaze me. From salads all winter to dried tomatoes in the summer, cold frames have kept my thumbs green (and sometimes shades of blue in January!) twelve months of the year.

People are sometimes surprised to find that after more than twenty-five years of intense gardening energy here, we still do not have a greenhouse. While I would like to have a greenhouse someday, I would not do without my cold frames for even a season. Not only are cold frames much cheaper and easier to build than greenhouses, they tend to be much more portable and therefore, in my opinion, more versatile.

It is this quality of mobility that has allowed me to develop a succession system that extends the season of various crops by about a month in the spring and in the fall. By successively rotating the cold frames to different beds and new crops (from hardier to more tender, and from January to June), I am able to keep virtually  four times the area of plants protected in one season than if using a permanent greenhouse structure.

In order to verify all this for yourself, of course, you’ll need to build a cold frame. We use a variation of Elliot Coleman’s design. (See his books, The New Organic Grower and Four Season Harvest, for ideas.)  I suggest first finding a cheap source of glazing material and designing your cold frame around them. We were fortunately gifted with some oversized tempered glass doors (61/2’ by 31/2’) that have proved to be excellent though heavy. I can barely manage carrying a single pane by myself. Sashes, though easy to come by, are headaches in my opinion, due to the ease of breakage and the annoyance and potential hazards of chipped paint. Be sure to design some thorough way of strapping down your glazing. (Rubber bungees work well.)  I have regretfully shattered several panes due to insufficient protection from strong winds.

I’ll assume that you already have a cold frame or two. (We have about a dozen. Watch out–they’re addictive!) Now let’s get out in the garden. Next time there is one of those mid-winter thaws you should be ready to plant some greens. In fact, I never stop sowing.  I plant successions of salad greens throughout the winter whenever I can (about once a month). Be sure the ground is well thawed, since working frozen ground damages soil structure.

All it takes is a little sunny weather to heat up the soil sufficiently for germination. I find things germinate in about twice the time they would under more ideal conditions. In the winter I sow thick stands of tightly-spaced rows of lettuce mixes and other mesclun-type greens. Harvested as baby greens, they are ready in about two months (also about twice the usual). I have found that the smaller plants are much less susceptible to freeze damage than mature heads. If you harvest an inch above the crown you should get three to four cuttings. This winter I am alternating rows of spinach with other greens so that the spinach can take over in March, once the salad greens are spent.

I actually hope to also start my first root crops and peas the next time I am able. I plant both dwarf and tall varieties of peas at the back of the cold frame to be trellised later, once the cold frame moves onto other crops. That leaves plenty of room for carrots, beets, and whatever else you like toward the front of the frame. You should get your first tender samplings of these by May if they’re sown by early February. We start our onion seedlings at about this time, too, and transplant them into garden beds in April.

As I mentioned at the beginning, this is also the time I start my early tomatoes, as well as broccoli, cauliflower, cabbage, head lettuce, peppers, eggplants, and basil. Germinated indoors, these will eventually get potted up and moved to a cold frame (insulated with hay and blankets) in March. There they continue to grow until warmer weather, when more cold frame space frees up for their protection. I will describe how this works next month. For now, if you want those early fruits, get the seeds started!

I strongly recommend the Territorial Seed Company catalogue as a good source for certain seeds and for information on over-wintering crops in general. They even have a separate winter gardening catalogue. They have been a wonderful source for early determinate tomatoes (often bred by Dr. James Baggett, my hero), which are perfect for cold frames. My favorite is “Siletz,” though the more commonly available “Oregon Spring” is also good. This year I am trying a new Baggett creation called “Legend.” It’s supposed to be the first late-blight resistant tomato. Both are open-pollinated to boot!

Finally, I cannot conclude without saying a few good words about spinach. Whether you have a cold frame or not, this is a crop that all gardeners in this area should grow. For the past two years we have been eating fresh spinach salads from plants growing in the garden without any protection! Started in September, spinach gets to mature just enough to hold plenty of delicious sugary sweet leaves to fill bowlfuls of salad throughout the winter.

Though some leaves may get slightly discolored and limp with extreme temperatures, it invariably rebounds with warmer weather and will even grow some, given a string of mild days. Come March, these same plants will go crazy before bolting and will give you many pots of steamed greens.

Well, that’s all for now. Happy gardening!