Your Winter Garden: From Season Extension to Microgreens

Learn how to best continue your garden into the winter months with these winter gardening techniques; from season extension to microgreens.

forcing bulbs

Spring-flowering bulbs can be brought indoors and "forced" to bloom during colder months.

Photo by Fotolia/Grafvision

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Winter is a time of rest in the garden throughout most of the country. It’s a time when gardeners traditionally get comfy near the stove or fireplace, delve into the new season’s seed catalogs, revisit the last season’s triumphs and disasters, and plan for next year.

But sometimes, gardeners miss getting their fingers in the dirt. They miss those summer chores, and they miss watching green things grow. If you’re one of these gardeners, don’t despair—there are ways to garden right through the winter. At the very least, if you have an indoor space where you yourself are comfortable, you have a place where something can be grown; it’s amazing how even a few plants can lessen the winter blahs!

Outdoor Season Extension

Every plant needs suitable conditions in which to grow. Season extension means providing that climate before or after it occurs naturally. Usually this means protecting plants from wind and extreme cold. For any specific crop, you want to keep or create optimal conditions for as long as possible. This could mean extending the growing season further into winter than would be possible naturally; it can also mean warming things up early to get a jump on spring. Either way, the net result is to give you more gardening enjoyment and more great produce from your garden!

The English used heated glass structures to house orange trees and other exotics through the winter. The French used cloches, small bell-shaped glass domes, to keep vegetables warm until the weather was ideal. These days we have other materials that are much lighter and less likely to shatter from impact, though glass is still a viable option.

A wonderful material available today is called floating row cover. Brand names include Remay and Agribon. It comes in different weights for varying degrees of frost protection, the heavier weights offering the most protection, although arguably at a cost in light penetration. Water and air pass freely through this material, so you don’t have to worry about removing it on warm days, or do much watering unless there hasn’t been enough rain. Row covers also protect their inhabitants from drying winds. Sometimes only a few degrees of temperature can make a huge difference. The first time I used this material I was amazed at the rate of growth of the salad greens underneath. The heaviest grade claims protection from 15 degrees of frost. That’s quite a claim, meaning you could keep a frost-free environment when outdoor temps are dropping below 20 degrees. Such performance probably assumes the best possible configuration; I would expect more modest results in the rough-and-tumble of my own garden. Still the value and simplicity of this one single tool cannot be overstated.

For serious protection and very early starts, a hot house is ideal. But short of that expense, hoop houses or low tunnels covered with clear plastic are great for season extension. Hoop houses are tall enough to walk in, and low tunnels are just tall enough to provide a moderated mini-climate for the plants underneath. The first time I used a low tunnel to get an early start on corn, the seed germinated in three days, while it was still quite chilly outdoors. The temperature within was a balmy 90 degrees Fahrenheit. But the drawback is that temperatures can really soar on unseasonably warm days, so you need to monitor the weather daily and open the ends to draw some of the heat out on occasion – less and less, as winter tightens its grip, more and more in late winter until it’s time to remove them. I also use low tunnels to protect tender perennials and to grow cool-hardy crops well into the winter.

Author Eliot Coleman is a phenomenally successful year-round gardener in Maine, where winters are harsh and very long. He combines high tunnels (or unheated greenhouses—label them how you will!), with floating row cover further protecting his plantings within. He likes to say that every layer of covering moves the effective temperature conditions one climate zone south. He gardens in USDA Hardiness Zone 4, but with his arrangement, his plants experience the equivalent of a Zone 6 or Zone 7 winter. That’s something like Arkansas winter conditions inside, when outdoors it’s all Maine—not bad!

Coleman stresses, though, that not much growth occurs in the couple of months around the winter solstice (about December 21). The reason is not so much temperature, but rather light levels. At higher latitudes, the sun is just very low in the sky in early winter, even at mid-day. Total light intensity is therefore less, and the length of the days is very short too. So the plants may not actually be growing much right then. But ideally, they will have made plenty of growth beforehand. Coleman often says that at midwinter, he does no gardening at all, but only harvesting! Within these limitations, he has been very successful with the following cool-season crops: Lettuce, spinach, corn salad, carrots, turnips, Asian greens like pak choi. In other words, all the usual cool-season stuff. Naturally, gardeners farther south have milder conditions and longer days in winter, and so the spectrum of potential winter crops increases as latitude decreases.

Another, traditional method of bringing plants into or through a winter’s chill is the cold frame. This is any ad hoc structure utilizing old window sash, which really amounts to constructing a mini-greenhouse over the mature plants. The windows can be supported by 1-2 foot high frames made of scrap lumber. Or small bales of hay can be placed immediately to the north of the bed, with the windows propped upon them, facing south. Any arrangement will do, provided that it encloses the air immediately surrounding the plants. If blankets, old carpets or tarps can be draped over the structure at dusk and removed the following morning after things warm up, the protection is even more pronounced. Not pretty, perhaps, but serviceable, as generations of home gardeners have known.

So much for outdoor arrangements. Indoors the outlook is brighter, literally and figuratively! There are numerous options available to winter-weary gardeners: growing under lights, in bright windows, sprouting, growing microgreens, bulb- and flower forcing—the list is nearly endless!

Microgreens

Microgreens are a superb winter crop to grow, whether you grow them indoors n a window-sill or under lights, or outdoors in a cold-frame, low-or high-tunnel, or a greenhouse. Microgreens are super-healthful young greens, usually harvested when only a couple of true leaves have developed. In good conditions, this means you go from seed to harvest in as little as two weeks! They pack a big nutritional punch, since the tiny young plants are really just gearing up for further growth; they have a lot of nutrition. And while they do need proper light to achieve perfection, they’ll still make a pretty respectable crop in somewhat lower light levels, since the young plants are still living off of stored nutrient reserves from the seed. Heating mats, the kind you’ll be using under your tomato seedlings next spring, can be very useful when growing your microgreens on a cool windowsill; a small fan is good insurance against disease in warmer, humid conditions, as in a lush planting under grow-lights. Types to grow include any cool-season greens you enjoy—beets, arugula, lettuce, chard, turnips, mustards, spinach, kale, radish, peas, sunflowers, and even some herbs like dill or fennel. Seeds are sown very close together, since the plants will be harvested when tiny. They are harvested by cutting just above soil level, using scissors, a knife or even an electric knife if you’re growing them in flats. Baby greens are grown the same way as microgreens, with the exception that seeds are spaced a bit farther apart at sowing. Harvest of baby greens takes more like a month, and is less tedious since the plants are larger. Either way, flavor and nutrition are superb!

Indoors, The Season Never Really Ends...

Indoor gardening under lights has really come into its own over the last decade or two. There are numerous options available, and some of them get pretty spendy. LED’s, halogens, high intensity discharge, high intensity fluorescents—it’s a long list, and it’s important to evaluate carefully and choose the best type for your situation. Whichever sort of lighting you purchase, make certain it is safely installed, according to the manufacturer’s recommendation, and be sure to follow instructions regarding placement of the plants as well. Some lighting gets very warm, other types may not be very intense, and so it’s crucial to allow the correct distance between the lights and the plants.

You need to pay strict attention to the photo-period, or day-length you’re creating in your indoor environment. It might seem counter-intuitive but the longest days do not necessarily make for the best growth. Some plants will react to super-long days by running to seed. Lettuce and spinach will quickly bolt in days running much above 14 hours; onion seedlings might actually bulb up under long days. That’s not so good if your onion plants are small—the bulbs could literally be the size of a pea. So it’s important to understand the needs of your indoor crops and fix the length of their photo-period accordingly. You can arrange timers to make it easy on you, and consistent for your plants.

Not into such high-tech gear? I’ve had decent results with plain old “shop lights”, utility-grade fluorescent fixtures, widely available and inexpensive. I try to either use grow-light tubes, or at least to combine one “warm” (reddish) tube with one “cool” (bluish) tube per fixture. The results have been mediocre, compared to those of some friends who use top-of-the line systems, but certainly worthwhile for the time and resources spent on them! A big disadvantage is that, since these are not high-intensity bulbs, the tubes must be positioned immediately above the foliage for best results. The light simply isn’t strong enough to grow good plants if it shines down from the ceiling! And I find that even were leaves inadvertently touch the tubes, they are cool enough that the leaves are seldom harmed.

What about plain-old windowsill growing? It’s not impossible, but it’s not as easy as it might seem, either. Winter sunshine is far less intense than summer’s, but some plants can grow or at least stay healthy until growth resumes. The only windows likely to succeed would be south-facing ones, for in winter the sun is at a low angle in the southern sky (at least in the northern hemisphere!). Then too, on cold winter nights, the window-sill environment is likely to be markedly colder than the room’s interior; it gets even worse if curtains are drawn, isolating the poor plants right next to the cold glass! But it can work if the plants are removed from the windowsill at night and held at room temperature until next day. Bothersome, yes, but I can attest it works, if you want success badly enough to spend the time. The best plants to grow under these conditions are lettuce, spinach, other cool-season stand-byes of small stature, as well as herbs and microgreens. Amaryllis and other tropical bulbs are handled the same way, except that they do like warmer temps, and they don’t need a chilling period to initiate root formation. These types are often grown indoors in pots, start-to-finish, for many years.

Forcing Bulbs

Spring-flowering bulbs are great candidates for forcing. By the time the plants die down in summer, these bulbs have stored away all the energy they need to yield vibrant color and often superb fragrance the following spring. They are easy to coax into bloom. Dormant bulbs are potted in soil or placed in “forcing vases” which are filled with water. Either way, these are held in cool conditions, under 50 degrees Fahrenheit or even cooler, for a few weeks to allow roots to develop. At that point the plant begins to make new growth, and should be brought into warmer, well-lit conditions. Room temperature is ideal. The plants make steady growth, and in a few weeks time burst into full bloom, making charming specimens or focal points or room accents. After blooming, plants can either be discarded or else maintained until planted outdoors or until dormancy sets in again.

Overwintering in Containers

Gardeners not blessed with a greenhouse can still enjoy plant varieties that would never survive outdoors in their climates. Moreover, caring for the plants is pleasant and gardeners can often get some sort of a winter harvest as well. A variety of plants can be either grown in containers year-round, or lifted from the garden at summer’s end and potted and brought inside ahead of frost. Ordinary temperate zone garden favorites that respond well to this practice are peppers, lemongrass, stevia, basil and other herbs. However, sub-tropical or less tender plants are also handled this way, where the winters are too severe to allow them to survive outdoors. Plants like pomegranates, citrus, and figs can take some freezing, but not super-cold temps, and can only be grown in cold-winter areas by affording some sort of protection. Obviously, true tropical crops like banana, passion fruits naranjilla, pepino, tamarillo, etc, can only be handled this way if some sort of a sun-room is available for the plants to at least continue making slow growth during the winter.

Sprouts

Sprouts are said to be the most nutritious “greens” of all, and sprouting is very simple to do—it doesn’t even require soil. All that’s necessary is good, clean seed for sprouting, and some sort of where the seeds can be held. This needs to allow for occasional watering of the seeds and immediate drainage, and ample air and space for development of the tasty sprouts. Various arrangements of jars and colanders are the usual expedient, or you can purchase simple, purpose-made devices. So long as the temperature is correct and the proper balance maintained between air and moisture around the seeds, success is virtually assured. Good candidates for sprouting are any edible plants whose seed is not objectionable to eat. (Some, like beet or sunflower seeds, could be a bit much!) Alfalfa, wheat “berries” and mung beans are classic, of course, but a wide range of brassicas (cabbage relatives) and others are often sprouted as well. Sprouting takes only a very few days, and must be repeated many times in the course of a winter to assure a consistent supply.

Another seldom-used technique was more widely appreciated by our ancestors: forcing. It really means encouraging a dormant root to grow and yield flower or food. The classic veggie for forcing is the Witloof, or Belgian Endive. This lettuce relative would have been grown outdoors in late summer. In fall, the roots would be lifted and trimmed, and the tops cut back to about a half inch above the crown of the plant. The roots would be stored in moist sand in as cool conditions as possible, but above freezing. Then, periodically, some of the roots would be brought into warmer conditions, 60 degrees Fahrenheit being recommended. The roots would be positioned upright, still in moist sand, and within a few weeks succulent new shoots appear. These are often seen at markets, even mainstream ones, and are mild, delicious and wonderful fare in the depths of winter, whether used braised or raw in salads.

Few gardeners realize, however, that other types of roots can be forced with equally good results. First of all, relatives of witloof are all worth a try: these include radicchio, chicory, and plain old lettuce. Dandelion is another, and even wild roots may be harvested and used this way. Other plants that can be encouraged to yield tender, delicious leaves include turnips, rutabagas, salsify, beets, and even onions.

So curl up by the wood stove this winter, by all means. Enjoy the season for what it is. But for many of us, winter’s a time of tenderly caring for a few plants. It’s their rarity that makes them so alluring and precious. Tending to winter plantings is a great joy that more winter-weary gardeners really should experience!


Randel A. Agrella has overseen rare seed production at Baker Creek since 2005. He writes and lectures extensively, and owns and operates AbundantAcres.net, which has grown and shipped strictly heirloom, chemical-free veggie starts and plants, since 2004. He has recently relocated to Maine, and you can follow the development of his organic micro-farm, Parsnippity Farm, on Facebook.