Just as for my spring garden, I prefer to start plants that are going into the greenhouse as transplants if at all possible. Starting with transplants is even more important in a greenhouse, actually, since the greenhouse may still be too hot to direct sow crops in the late summer, when some crops need to be started.
- Lettuces are quite resistent to frost, though they are not as cold hardy as some other winter garden plants. Some varieties are better adapted to cold weather and short days, so study your seed catalog descriptions. I always grow a dozen different varieties—I guess I’m easily bored with only one or two textures, colors, and tastes.
- Chicories are my favorite winter salad. Indeed, during the height of winter—January and February for me—you can forget your mesclun and fancy lettuces, give me chicories! And if you’ve been turned off to stringy, bitter, tough endives and escaroles from the supermarket, be assured that—in the reduced light and chill of the winter greenhouse—chicory’s bitterness is tinged with sweet, and the stringy toughness is replaced by a delightful juicy crunch. Chicories come in many shapes, colors, and types: round heading, tall heading (sugarloaf, the chicory equivalent of a Romaine lettuce), open heading (escarole and endive), cut-and-come-again leaf types (catalogna, cardoncella), radicchio, mini-headers of which you use whole tiny heads in salads (grumolo), even chicories with edible roots—all in a riot of beautiful colors, often variegated: green, rose, salmon, red, pink, etc. (An unusually good source for chicory seeds is Seeds from Italy. Be careful, though: Last time I was on their site I ordered nineteen varieties!)
- Less well known salads include mâche and edible chrysanthemum. Some are astoundingly cold hardy, such as claytonia (or miner’s lettuce) and minutina (Herba stella). And don’t forget scallions as an easily grown addition to winter salads.
- Spinach is extremely cold hardy. I prefer young spinach, so I make successive sowings throughout the winter growing season. During the darkest part of winter, of course, the spinach will not make much progress. However, with the coming of longer days it will grow rapidly.
- Crucifers—including mustards, raab, Oriental greens such as pak choi and tatsoi, etc.—are tasty and nutritious “potherbs,” and are excellent candidates for cold-weather growing.
- Chard (or Swiss chard) is simply a type of beet (Beta vulgaris) bred for its large tender leaves and rapid re-growth, rather than its roots. It is cold hardy and productive.
- Green onion and garlic tops make great cooking greens. When I plant my garlic crop in the garden in the fall, I use the biggest cloves only. The smaller cloves go into the greenhouse for growing “garlic scallions.” We also sort out the smaller stored onions, or the ones that have begun sprouting, and plant them in the greenhouse for their beautiful and nutritious green tops.
Parsley, cilantro, leaf celery, dill, and other cold hardy herbs make great additions to winter salads and to the soup pot. They are easy to grow.
Brassicas that head (such as cabbages and broccoli) are more likely to develop large, tight heads if grown in the late-winter greenhouse rather than in the fall. (Some varieties are more suited to greenhouse production than others, so study your seed catalogs.) An exception is kale, which is an excellent crop for the fall-winter greenhouse if you make an early enough start on your transplants.
What About Root Crops?
In my experience, root crops such as beets or carrots, even though cold hardy, are also not suitable for planting in the fall greenhouse—they will grow, but do not receive sufficient energy in the shortening days to “make root.” I have, however, had excellent results growing carrots, beets, potatoes, and daikon (as well as the smaller radishes) in the late winter greenhouse, harvesting these crops up to two months earlier than their siblings in the garden.
Overwintering Tender Perennials
Here in Zone 6b, certain of the “tender perennials”—such as rosemary, tarragon, and white sage—may or may not make it through the winter. In the late fall, I dig up these herbal allies and plant them temporarily inside the greenhouse. With the additional protection, they survive the winter easily, and are ready to go back out to their accustomed places come spring.
An Early Start on Warm Weather Crops
All warm-weather crops can get a much earlier start in the late-winter, early-spring greenhouse. I start tomatoes, peppers, and eggplants as early as mid-January to the end of February. (I start them under grow lights in the basement, then move them into the greenhouse when they get too big for the grow bench.) As long as I pot them on as needed to prevent their getting potbound, I have big plants that are growing fast and which experience no check on their growth when it is warm enough to plant them out in the garden. Using this strategy, I get ripe fruits a month earlier than I would if planting less developed plants.
Actually, I plant a few extra-early tomatoes in the greenhouse itself, to savor that first vine-ripened tomato earlier than any plant in the garden could possibly match.
Another warm-weather crop I like to start in the greenhouse is sweet potatoes. I choose a few of the tubers that have stored best of all through the winter, half-bury them horizontally in moist sand, and keep them in the warmest spot in the greenhouse until sprouts start coming up from the mother tuber. By the time the weather has warmed sufficiently to plant sweet potatoes, the “slips” have numerous dark green leaves and their own roots, and I snap them off for transplanting into their garden ridge.
Green Forage for Livestock
Winter can be a difficult time for our livestock, especially those lucky ones whose owners have given them access to pasture during the green season—how they miss those great greens in the dormant time of the year. To offer fresh green forage in the winter (which is beneficial even in small amounts), we can reserve some of the greenhouse for growing “green chop” for our goats, cows, poultry, etc. Grain grasses (wheat, barley, rye, oats), mixed crucifers (rape, mustards, turnips grown for the leaf, etc.), and peas are excellent candidates for cut-and-come-again green forage.
Another possibility is sprouting some of the grains we feed our livestock. Soak the grains, lay out in a thick layer in plant trays (or even directly on greenhouse beds), cover lightly with straw or other loose organic material, and allow to sprout. Once the shoots have grown an inch or two and “greened up,” offer them to your wards and see what happens.