Johnny's Winter Growing Guide
Ranked by Reliability for Winter Growing Success
Feedback received from northern growers has provided a ranking of crops proven successful for winter growing regionally. In order of popularity and degree of reliability, these crops fall into 3 tiers. Hardiness, adaptability to winter growing, and quality and quantity at harvest time also factor into the ranking.
- Baby Leaf Brassica Greens
- Pac Choi
- Choi Sum
- Broccoli Raab
- Bunching Onions
Branch Out or Specialize In
Numerous additional crops can be produced in winter, depending on your climate, risk tolerance, and market demand. You may, for example, gain success with claytonia, mâche, late-sprouting broccoli, parsley, or other roots, flowers, and herbs.
Crop by crop, here are some of our top performers in the winter harvest and overwintering slots…
Winter Growing, Crop by Crop
Winter spinach is exceptionally sweet and flavorful. The plant builds up sugars in response to cold, which protect its cells from bursting in freezing conditions. Spinach is also easy to grow, making it a good first choice if you are new to winter growing.
Sow your winter-harvest spinach 35–50 days before the start of the Persephone period. Spinach does not germinate well under the warm conditions that often prevail at this time. To optimize germination rates when it's warm at seeding time, irrigate before planting, to cool the soil. To ensure your desired plant density, you can alternatively start spinach in plugs or paperpot trays and grow to transplant size (two true leaves). Some growers configure LED-lit racks or shelving units in their basements to provide a conveniently cooler, indoor seed-starting environment at this time of year.
Seeding earlier will produce earlier harvests that will continue to grow and remain harvestable over the course of the winter. Planting in late fall, with the plants reaching approximately an inch in height by the solstice, is likely to produce harvestable spinach by February.
These spinach varieties can also be resown in winter for baby leaf production in early spring. They will grow quickly in spring and must be harvested before bolting.
In some regions, overwintered spinach is prone to downy mildew infection. Make sure you select varieties that are resistant to the races of downy mildew, if any, that are prevalent in your area. (Check with your Cooperative Extension Service.)
Like spinach, kale is much sweeter in the coolest months of the year.
All varieties of kale can be grown in the winter, but curled-leaf varieties are a bit hardier, and make for bigger bunches more quickly — you will spend less time harvesting the kale and your bunches will look fuller. Green curlies and Russian types grow the fastest and are the most winter hardy, red curlies grow a little more slowly, and lacinato types grow very slowly in the winter and are the most sensitive to tipburn from the cold.
Seed kale in late July or early August for transplanting in September. Cover with lightweight row cover to exclude a variety of insect pests. Harvest from late October through March by clipping the leaves from the bottom up. It may not be necessary to protect kale if the plants are fully harvested by the time the coldest winter temperatures hit.
Kale plants of varying size can be kept overwinter in low tunnels, for harvest in early spring. The quality of the large leaves remaining in spring will depend on the severity of the preceding weather. Surviving small plants will quickly begin producing new growth.
Numerous brassicas make good winter production candidates. Pac choi is one due to the thickness of its stems, which can endure a measure of freeze damage. Asian leafy greens such as komatsuna, mizuna, and tatsoi, as well as other brassica greens such as arugula and mustards, will regrow and can be cut multiple times throughout the Persephone period. Plants are less likely to incur cold damage when repeatedly harvested at the baby leaf stage rather than grown to full size, but may experience winter kill if planted too densely.
Choi sum ('Hon Tsai Tai' and 'Green 70D Improved') and broccoli raab ('Spring Raab'), too, are suited to winter production, most reliably in milder regions, as their stems and buds can be freeze-sensitive.
Because they are all very cold-hardy, claytonia and mâche can often be grown in an unheated hoophouse without a second layer of row cover. While they may not grow significantly during the Persephone period, they can be harvested during those darkest weeks.
Greens for winter harvest should be planted from August through October for harvest from September through March. Soil temperature when seeding should be 70°F (21.2°C) or lower, to optimize germination rates.
All of these greens will grow slowly through the winter for intermittent harvests during the coldest and darkest weeks and more uniformly into the spring for more regular harvests. For example, mâche planted in late September in the tunnel here in Maine is typically ready to be harvested in January and does not bolt until early March, while claytonia becomes full and beautiful as it emerges from the Persephone period, with lovely little flowers.
Chicory adds intriguing diversity to a winter greens collection.
Endive and escarole types (Cichorium endivia) are not quite as cold-tolerant as other types, and can be expected to behave similarly to lettuce.
Radicchio types (Cichorium intybus), however, shine in the winter tunnel, with superior cold-tolerance, eye-catching colorations, patterns, and shapes, and sweeter flavors that are not always as achievable at other times of the year.
It can be tricky to pin down an ideal planting date for consistent heading of chicories. We recommend sowing a few successions to help increase your chance of success if heading types are your target.
Young radicchio planted in the fall, unheated tunnel can likely overwinter with just a single layer of row cover. By late February they will start rapid regrowth, offering an extra-early harvest of unique, tasty greens to add to the mix.
Although hardy and reliable, chicory does take longer to mature than other winter "greens" and is less well-recognized by some customer segments than others; some customer education may be useful to assure its ROI potential.
Cilantro should be sown mid September to early October in a protected structure such as a high tunnel. With mild flavor and tender leaves, overwintered cilantro lends itself well to harvesting at baby leaf maturity.
Cover plants with heavy-weight row cover when temperatures dip below freezing in the structure, but try to uncover when temperatures warm back up, to better expose the plants to sunlight and allow for air flow.
Cilantro plants will grow very slowly through the depths of winter, but take off in late winter to early spring, with harvests possible from March through May.
"They were amazingly hardy and had little cold damage. We used 1–3 layers of row cover, but have a temperature monitor under the rowcovers, and it got down to the high teens on several nights. The only one we see with some damage is Green Incised Leaf, but it is minor….
"All in all, love it!"
— Sandy Arnold, Pleasant Valley Farm, New York
Lettuce is less cold-hardy than many greens, and fares best in a partially heated greenhouse or under a low tunnel within an unheated hoophouse. We suggest harvesting the lettuces before they're required to endure the coldest temperatures post mid winter. We also note the young leaves of salad mix tend to be less susceptible to freeze damage than mature lettuce heads.
Recently, growers in the north have been reporting some success with Salanova lettuces grown for mini head production and cut-and-come-again (CCA) salad mix in unheated high tunnels. Salanova has also excelled in winter trials at our own research farm in Albion, Maine. Setting out transplants in late September, and covering them with two layers of supported row cover, inside the tunnel, produces nice mini heads with minimal leaf damage for winter harvest.
One limiting factor in high tunnels is the filtering of sunlight that decreases the vivid red color of some lettuce varieties. For winter growing, we recommend 'Five Star Greenhouse Lettuce Mix' for its downy mildew resistance as well as the capacity of the red varieties in the mix to hold their red color. During winter months, varieties in some mixes may have varying growth rates. Some growers prefer to plant each variety individually and mix them after harvesting.
Radishes should be sown September through October for harvest through December. They can be covered with lightweight row cover to conserve heat or preclude flea beetles if necessary.
Although radishes are generally quite cold-tolerant, they will become spongy if frozen hard repeatedly.
You can direct seed turnips in the fall. Plant enough seed to provide for a long winter-harvest period, and lay row cover over the crop if flea beetles are a problem.
Be advised that turnips will not hold into the spring, however, and will bolt by March in the tunnel.
Winter-harvest carrots are super sweet. In addition, they are orange — unlike most fresh winter-harvest crops — adding a welcome touch of color to the produce you offer for sale.
Carrots should be direct-seeded in early August for harvest from Thanksgiving through Christmas. If grown under row cover, their tops will be protected. A display of bunched carrots with attractive tops brightly signals freshness to prospective customers.
Carrots can also be successfully overwintered as young plants, to grow and reach harvest size in early spring.
Bunching Onions (Scallions), Spring Onions & Leeks
Bunching onions, which include scallions, can be grown for spring harvest but require ample lead time. They can be planted in either low or high tunnels, but we suggest low tunnels so they are not occupying the more valuable real estate within a high tunnel all winter.
Direct-seed scallions in August, and begin harvesting when they reach the desired size. For spring harvest, we start ours in the third week of August. Use our planting chart to determine the best date to start yours. (To harvest them in the winter, they would need to be started in early August or even earlier.)
Different varieties are preferred for winter-harvested scallions than for overwintered scallions. For late-winter harvest, 'Evergreen Hardy White' is good and cold-hardy, but it will bolt in the spring if overwintered. For overwintering, we suggest 'Deep Purple'.
Some varieties of fast-growing onions can be overwintered in low tunnels. Onions for overwintering should be sown in late August to early September, and transplanted out in late September to early October with the goal of having them reach the size of a pencil (about 4–5 leaves) before the hard freeze in November. If they make it through the winter, you will have "bunchable" spring onions by late May to early June.
Many varieties of leeks are winter-hardy to varying degrees. Protection in tunnels or by row covers will further enhance their survival. 'Lexton' and 'Bandit' are particularly winter-hardy leek varieties.
The Bottom Line
Winter growing is not a simple process with a guaranteed return. If you have an interest and the required resources, however, it can be rewarding in many ways. Chief among these:
- Your winter harvests can help you build and retain a customer base, as well as retain valuable employees.
- Many growers find that fresh greens nicely augment a selection of winter storage crops at winter farmers' markets and in CSA distributions, where there is a growing expectation for local diversity.
- Fresh, locally grown crops command a premium throughout the winter and the shoulder seasons, being both in higher demand than the same crops in summer and generally unavailable in the supermarkets.
- Winter-grown lettuces and other greens are different from, and in many cases superior to those grown outdoors during the main seasons or trucked in from elsewhere.
If you complete construction of your first new high tunnel in late summer, you will likely want to plant something right away. That first winter harvest can be very inspiring. For those with just one tunnel, the wisdom of ripping out high-return crops like tomatoes, cucumbers, and peppers from the tunnel in late summer may seem misguided at first. But as winter draws closer, the quality and quantity of those crops will decrease. Your best decision may be to replace heat-loving summer crops with those that perform well during the darker half of the year. By combining clever succession strategies and subsequent construction of additional tunnels, you can reap the many benefits of winter growing.
- Intro to Winter Growing
- Scheduling Guidelines for the Winter-Harvest High Tunnel
- Winter-Harvest Crops • Planting Chart
- Winter Production in the High Tunnel
- Overwintering Scheduling Guidelines
- Overwintering Crops • Planting Chart
- Protection Methods for Overwintering in Low Tunnels
- Focus on Crops & Varieties for Winter Growing
- Overwintering Onions from Seed