Winter farming is an art that combines knowledge, precision, and passion. For growers, producing fresh greens and lettuce that can be grown in winter in a greenhouse not only provides a steady income but also serves a loyal customer base eager for high-quality produce during colder months. Growing greens in winter requires understanding principles such as frost hardiness, using double-layer protection, managing limited daylight, and scheduling planting dates according to your climate zone. These strategies can transform your winter greenhouse into a productive haven.
But winter crop spacing also matters!
As daylight decreases, adjusting row spacing helps plants get more light and thrive. Want a quick reference? Get our free spacing chart for winter plantings!
Tested and Proven Winter Growing Methods
As the author of The Winter Market Gardener, I’ve spent years refining these techniques, building upon the pioneering work of Eliot Coleman. At Ferme des Quatre-Temps, we’ve conducted trials to optimize crop selection, planting schedules, and environmental management. The following seven salads and greens have proven to be reliable and profitable in our winter greenhouses. Let’s explore why they are essential for any grower’s winter repertoire.
Lettuce that can be grown in winter in a greenhouse: tips for successful cultivation
Lettuce is a staple in winter greenhouse production. While less frost-tolerant than spinach or arugula, it can still thrive in winter with proper care. Hardy cultivars like ‘Winter Density,’ the French ‘Merveille des Quatre Saisons,’ and ‘Dragoo,’ a mini-Romaine type, perform exceptionally well. Timing is crucial; seeding should align with your zone’s daylight and temperature patterns. In the Northeast, lettuce should be started by transplanting 30 days prior to the desired transplanting date—ideally no later than the first week of October. This allows the roots to develop properly before the cold sets in.
Once the crop is well-established, it’s important to harden off the lettuce by gradually acclimating it to colder temperatures. This process can be done by slowly opening the roll-ups or ventilation panels of the greenhouse over a period of several days. Start by exposing the plants to a small amount of cooler air in the morning and then gradually increase the exposure to the colder outside temperatures during the day.
This gradual transition helps the plants adjust without experiencing shock from sudden temperature changes. Hardened plants develop stronger cell walls and better resistance to frost, allowing them to withstand light freezes and avoid damage when real cold nights arrive. The hardening-off process also helps lettuce develop more robust, thickened leaves that are better suited for winter conditions, ensuring better yields and flavor as the winter progresses
For best results, lettuce should be grown under double-layer row covers to shield it from light frosts. Additionally, maintain steady watering and ventilation to prevent rot, as excess moisture can be detrimental in colder weather. Consistent airflow and moisture control are vital to prevent fungal issues like powdery mildew.
For more detailed guidance on winter vegetable production, consider consulting “The Winter Market Gardener”
Types of greens to grow all winter in a greenhouse
1. Arugula
Arugula has become one of my go-to types of greens to grow in winter, despite its initial reputation as delicate. Its rapid regrowth and ability to thrive in low-light conditions make it a star in a minimally heated greenhouse. Arugula diversifies a salad mix, offering a peppery flavor that customers love, especially during winter when its taste becomes milder.
For continuous winter harvests, we plan two to three fall seedings spaced 7 to 10 days apart. Arugula grows best in six rows per bed, optimizing sunlight penetration and airflow. Early harvests, typically 30 to 40 days after seeding, involve using a sharp knife to ensure clean cuts above the growing tip. Removing dead leaves after each cut improves regrowth and reduces fungal diseases.
While arugula can survive in unheated greenhouses, it benefits greatly from minimal heating. In colder conditions, we protect it with heavy row covers on nights when temperatures drop below 23°F (−5°C). Cultivars such as ‘Astro’ and ‘Esmee’ have performed consistently well in our trials.
2. Spinach
Spinach is winter’s undeniable superstar. It’s definitely the best type of greens to grow in winter. Its sweet, rich flavor and robust texture make it a customer favorite. Spinach thrives in cold conditions, and its quality improves as temperatures drop, thanks to the concentration of sugars that act as natural antifreeze.
We’ve found transplanting spinach to be more effective than direct seeding. Starting spinach in a nursery tray allows us to transplant it into high tunnels after summer crops like peppers and tomatoes are removed. This method ensures uniformity and higher yields. Spinach is harvested weekly by picking outer leaves individually, ensuring the plant continues to grow.
In unheated greenhouses, spinach withstands freezing conditions, provided it is protected with row covers on the coldest nights. In minimally heated greenhouses, its growth is even more vigorous, particularly in early spring when demand peaks. Varieties like ‘Auroch’, ‘Kolibri’, and ‘Space’ have shown exceptional performance.
3. Tatsoi
This Asian green is highly resilient and a fantastic addition to winter salad mixes. Tatsoi’s spoon-shaped leaves and mild flavor make it both visually appealing and versatile. It can tolerate significant frost and thrives in unheated greenhouses, although minimal heating improves regrowth and reduces stress during prolonged cold spells.
For best results, sow tatsoi in late summer or early fall. Harvest it as a cut-and-come-again crop or as individual rosettes for a steady supply throughout the season. Adequate spacing ensures airflow, reducing the risk of fungal diseases. Tatsoi is particularly well-suited to compact spaces, allowing growers to maximize productivity in their winter greenhouses.
Additionally, monitoring humidity levels is essential, as excess moisture can lead to disease. Proper soil drainage and timely weeding also contribute to healthy and consistent growth.
4. Claytonia
Claytonia, also known as miner’s lettuce, is a winter wonder with its unique round leaves and delicate texture. It thrives in cold conditions and requires minimal light to grow making it an excellent choice among the greens to grow all winter in a greenhouse. This crop is perfect for unheated greenhouses and provides consistent harvests throughout the winter months.
Sow Claytonia densely in four rows per bed and harvest entire plants or individual leaves as needed. Maintaining consistent moisture levels without overwatering is crucial, as the plant is sensitive to both drought and excess wetness. Claytonia’s cold-hardiness allows it to thrive even during harsh winter conditions. Its slightly tangy flavor adds diversity to salad mixes, making it a customer favorite.
One notable advantage of Claytonia is its extended harvest window. Once mature, it can be harvested repeatedly over several weeks. It tolerates colder temperatures than many other greens, ensuring reliable production even during frosty spells.
5. Mâche (Corn Salad)
Mâche is another cold-loving green that excels as one of the best greens to grow all winter in a greenhouse. Its nutty flavor and velvety texture make it a customer favorite. Mâche thrives in low-light conditions and can withstand freezing temperatures, making it ideal for unheated or minimally heated greenhouses.
For successful mâche cultivation, sow densely in mid-September using a precision seeder. The crop matures in approximately 60 days, with each rosette harvested in a single cut close to the ground. While mâche does not regrow after cutting, its long shelf life allows harvests to be extended over several weeks. Proper soil drainage is essential to avoid rot, particularly in wetter conditions.
Later seedings can overwinter in high tunnels, providing early spring harvests. However, without minimal heating, these later plantings may not thrive. Mâche should be harvested before May, as it bolts quickly in warmer conditions. Cultivars like ‘Vit’ are particularly well-suited for winter greenhouse production.
6. Mustard Greens
Mustard greens bring a spicy kick to winter salads and are highly adaptable to cold conditions. Their vibrant colors and bold flavors make them a popular choice for CSA shares and market displays. Mustard greens grow well in unheated greenhouses but benefit from row covers on frosty nights.
For continuous harvests, sow mustard greens in succession during late summer and fall. Maintaining good airflow is critical to prevent diseases, especially in densely planted beds. Harvest individual leaves for a prolonged growing period or cut entire plants for quicker turnover. Varieties like ‘Red Giant’ and ‘Golden Frills’ add both flavor and aesthetic appeal. These greens not only diversify your offerings but also thrive in cooler temperatures, ensuring a reliable crop during winter months.
Additional Types of Greens to Grow: Cress
Cress, often overlooked, is a hidden gem for winter production. Its peppery flavor and fast-growing nature make it a versatile and rewarding crop. Cress thrives in low-light, cold conditions, making it an ideal choice for unheated greenhouses. Its ability to grow quickly allows for multiple harvests throughout the season, providing a steady supply of fresh greens.
Sow cress densely and harvest it as microgreens or let it mature for larger leaves. It pairs wonderfully with other winter greens, adding a spicy punch to salads and garnishes. With cultivars like ‘Wrinkled Crinkled’ and ‘Peppergrass’, cress can be a standout in your winter greenhouse. Its minimal requirements and high yield potential make it a great addition to any grower’s winter lineup.
Principles for Winter Greenhouse Success
Producing these greens successfully in winter requires adherence to key principles. Frost hardiness is the cornerstone of winter farming. Selecting cold-tolerant varieties ensures your crops can withstand freezing temperatures. Double-layer protection, using both greenhouse plastic and heavy row covers, is critical for maintaining a stable microclimate.
Daylight is another limiting factor. In northern regions, the short days of winter slow plant growth significantly. Scheduling planting dates to align with the fall daylight decline ensures crops are well-established before growth slows. Understanding your zone’s specific conditions is crucial for timing.
Ready to Optimize Your Winter Crop Spacing?
An important step you can take to cope with shorter light periods is to alter crop spacing to allow more light to penetrate in the plant canopy. This can be achieved by widening the distance between rows. Most crops that are grown on 10 rows/bed in the summer will be grown on 6 rows/bed in the winter.
Get your free spacing chart for winter plantings
Finally, minimal heating can be a game-changer. While unheated greenhouses are viable, maintaining just above freezing temperatures can improve crop quality, extend harvest periods, and reduce labor associated with managing row covers. In this video, JM Fortier shares 7 of his best cold-hardy greens and lettuce that thrive in unheated or minimally heated greenhouse.
The challenge of producing greens all winter in a greenhouse
Growing salads and greens in a winter greenhouse is both a challenge and an opportunity. By selecting the right crops, understanding their specific needs, and employing effective techniques, growers can produce high-quality greens that delight customers and sustain farm profitability year-round.
Ready to master winter farming and extend your growing season? Join our Season Extension & Winter Farming Strategies course and gain the essential tools and techniques to harvest fresh vegetables all year round. Learn from JM Fortier, a leading expert in small-scale organic farming, with over 20 years of experience in winter production.
Sign up today and get immediate access to engaging video tutorials, detailed technical sheets, and expert advice to help you grow frost-resistant crops, boost your farm’s profitability, and contribute to local food sovereignty.
