Winter Lettuce Production
Growing Lettuce in the Winter
When we think of winter crops, we think of tough, leafy greens and durable roots that grow close to the ground and survive the low light and cold temperatures of winter, in part due to their robustness and strength. These crops are often delicious, sweetened with the frosts and hardy to the difficult growing conditions of the cool seasons. One crop that has many of these enduring traits but offers something a little more subtle and tender, is lettuce.
While lettuce can struggle with frost due to its high water content, lettuce tolerates cold weather very well and with proper management, can be overwintered in some capacity in almost every region.
While climates that remain temperate all year long have the advantage of outdoor lettuce production with minimal cover (using tools like row covers and low tunnels), many regions will need to rely on more serious season extension tools to keep the harvests coming. Planting in cold frames, heated and unheated greenhouses and high tunnels can shield plants from the worst conditions of the winter months while also boosting their growth through added warmth and maximized available sunlight.
Seeding of lettuce for winter production happens from late summer to late fall. When direct seeding lettuce into soil, the soil must be above 32° F for germination. Seed should be planted no deeper than ¼ inch and should be spaced based on the stage of maturity you wish to harvest. In the winter, lettuce is often harvested before full maturity as baby-leaf lettuces are more tolerant to the conditions of winter than full sized head lettuces. In this case, lettuce seeds should be directly sown in rows spaced 4-6 inches apart. For full sized heads, lettuce should be sown at least 10-12 inches apart.
Utilizing transplants can help dial in planting schedules and help better manage the precious real estate of covered growing areas. In the winter, using transplants can greatly improve the survivability of young plants when growing conditions worsen or periods of cloud cover further reduce the availability of light. Transplants are planted at a spacing based on desired stage of maturity at harvest with just enough soil to cover the soil medium holding the roots from the transplant tray. Ideally, planting lettuce on a warmer day with partial sunlight will help with transplant shock as well as irrigating at the time of planting.
A diverse and balanced mix of nutrients and high organic matter are required for healthy lettuce development. Compost, minerals and other organic approved fertilizers can help with productivity and resistance to pests and disease. Lettuce is considered a heavy feeder and that should be considered when designing crop rotations, selecting amendments and making plans for cover crops. Testing the soil of covered growing spaces in the winter will give the grower the best idea of what nutrients are actually available during the winter months.
Growing lettuces outdoors in the winter under row covers or using row covers as additional protection in unheated greenhouses and high tunnels is a great way to protect plants from frost. It is, however, important to note that the row cover will reduce available light and airflow which can cause problems for the lettuce crop. The low light and reduced airflow can create the perfect environment for foliar diseases and pests such as aphids and plants should be checked throughout the winter season for signs of infestation. It is also important to note that row cover will further reduce available light which can impact the expression of red color in lettuce leaves.
What the Plants Need
Lettuce requires a soil pH range of 6.0-6.5 for optimal growth. The soil should be well-drained to prevent stagnant conditions promoting rot, soil acidification and root diseases.
It is important to water your lettuce crop through the winter, noting that lettuce will require significantly less water in the winter months than what is typically required during spring and summer production. Drip irrigation is a great method for watering overwintering lettuces as managing the frequency and depth of the water is easy and efficient. Keeping water off the leaves of the lettuce crop will help the grower prevent the spread of foliar diseases.
While light is limited during the winter months, it remains an essential aspect of healthy plant development. When days and/or weeks of direct sunlight occur, plants may grow more quickly, especially if the temperatures remain mild. During periods of cloud cover, rain, and/or snowfall, plants may slow to what seems like a standstill. This makes days to maturity more variable in winter production than what is experienced during the spring and summer growing seasons. A head lettuce that typically takes 50 days to reach maturity may take 60-80 days, or longer as a result.
Varieties for Winter Production
When selecting varieties for winter production, it is a good idea to choose varieties that are cold tolerant and offer disease resistances.
Growers have found success using varieties included in our Eazyleaf Lettuce Collection including Ezrilla, Burgandy, Hampton, Brentwood, Buckley, and Ezbruke. These one-cut lettuce varieties are grown as head lettuces but can be sold as loose mixes. They can be harvested before full maturity and offered as mini heads or baby-leaf lettuce.
For a cold hardy lettuce mix, try our Yankee Hardy Lettuce Blend. Lettuces featured in the mix are cold tolerant and most have good downy mildew resistance, essential for winter plantings in regions with downy mildew pressure.
In warm climates like the Mid-Atlantic, Southeast, Southwest and southern California: Try varieties like Red Oak Leaf, Rouge d’Hiver, New Red Fire, Lolla Rossa, Spretnak, Newham, Winter Density, Vulcan or Kweik.
In more temperate climates found in parts of California and the Pacific Northwest: Try varieties like New Red Fire, Red Salad Bowl, Salad Bowl, Tango, Roxy, Lovelock, Newham, Vulcan, Spretnak, Newham or Australe.
Pests and Diseases
Due to reduced airflow, sunlight and often times an excess in moisture, winter lettuce is susceptible to contracting soil borne diseases and foliar diseases.
Some of these common diseases include:
Lettuce Drop Sclerotinia
Gray Mold Botrytis cinerea
Bottom Rot Rhizoctonia solani
Damping-Off Pythium spp. and Rhizoctonia
Powdery Mildew Erysiphe cichoracearum
Soft Rot Erwinia carotovora
Bacterial Leaf Spot Xanthomonas campestris
Pests are another issue for covered culture, especially in roomy high tunnels and greenhouses that served as a home for summer crops.
Some of these pests include:
Thrips Thrips spp.
Whiteflies Bemisia and Trialeurodes spp.
Two Spotted Spider Mites Tetranychus urticae
Aphids Aphidoidea spp.
Managing pests and diseases in covered growing plots during the winter season requires an active management role. While weed pressure may be reduced, any weeds or spent plants from the summer and fall growing seasons should be removed as they provide habitat for overwintering pests and disease. Ensuring that the plants get good airflow by removing row cover when conditions allow and holding the row cover above the crops with hoops or wire can alleviate disease pressure. Scouting for pests and diseases can also help you identify and remediate an issue before it results in total crop failure.
When it comes to lettuce, it is important to remove dropped leaves and plant debris from between each plant. Choosing varieties that have high resistance to disease can help crops stay healthy when conditions become less than optimal. Finally, crop rotation can help reduce or even eliminate the presence of soil borne diseases with at least a three-year rotation providing the best results. This can be challenging when it comes to high tunnels, greenhouses and cold frames as these spaces are generally high use and space is limited.
Harvesting and Post-Harvest Handling
Harvesting winter lettuce can be done with scissors or knives and should be done when the lettuce is as dry as possible. Lettuce can be harvested at any stage, depending on the desired size, and can be accomplished both by harvesting whole heads or cutting leaves. It is important to handle lettuce with care as it can lose quality quickly when bruised.
Lettuce is best stored already washed as the leaves themselves are at their strongest just after harvest. Going through the rigorous process of washing fresh prevents damage from handling. Lettuce should be cooled to around 32° F and stored around 34° F in a storage container free of ethylene producing crops. Properly cared for lettuce that is cooled and stored at the appropriate temperature can be viable for up to three weeks.