Growing Lettuce in a Greenhouse All Year Round: The Easy 2026 Guide!

By the AtmoSerre team

🥗 We're going to tell you something we often repeat to our customers: growing lettuce in a greenhouse all year round is one of the simplest and most satisfying things you can do with a garden greenhouse. Yet, it's also one of the most underestimated crops by beginners, who often mistakenly think that greenhouses are only for tomatoes, cucumbers, or exotic plants.

So no. Lettuce, that humble green leaf we tend to consider mundane, is actually an ideal crop to start with in a greenhouse, and especially to never run out of fresh greens on your table, come rain, snow, or frost outside. 🌿

In this guide, we will explain everything you need to know, truly everything: the best varieties to choose according to the season, how to prepare the soil, when to sow, how to water, how to manage heat in summer and cold in winter, and especially how to avoid common mistakes that make your lettuce yellow or bolt before it's even ready to harvest.

Welcome to the most comprehensive guide on growing lettuce in a greenhouse. 🌱

🌿 Why grow lettuce in a greenhouse rather than directly in the ground?

The first question we often get asked is this: "Is it really worth growing lettuce in a greenhouse when you can plant it directly in the garden?" And our answer is always the same: yes, and even more so than you might think.

Here's what a greenhouse concretely changes for your lettuce:

🌡️ Stabilized temperature: Lettuce hates sudden temperature fluctuations. In a greenhouse, the temperature doesn't drop from 20°C to 2°C overnight, which prevents shocks and accelerates growth.

🌧️ Protection from bad weather: Heavy rain can devastate a row of lettuce in minutes (especially young plants). In a greenhouse, your crops are protected.

🐌 Fewer pests: Slugs, snails, certain insects... They are much less present inside a well-maintained greenhouse.

📅 An extended season throughout the year: This is THE real argument. In open ground, you have a limited growing window. In a greenhouse, you can sow from January and harvest until December, or even continuously if you manage your rotations well.

🥗 Superior taste quality: Less water stress, homogeneous diffused light, regular growth... this is reflected in the plate. Greenhouse lettuces often have more crunch and flavor.

And all this, without being an expert. That's the beauty of growing lettuce in a greenhouse: it's accessible, fast, and incredibly rewarding. 🙌

🌱 The best lettuce varieties to grow in a greenhouse all year round

Let's be honest: not all lettuce varieties are equal when it comes to growing them under cover. Some tolerate heat very well, while others are remarkably cold-resistant. Choosing the right varieties is already half the battle won. 💡

🥬 Classic butterhead lettuces

These are the lettuces we immediately visualize: round, well-formed, with a beautiful dense heart. They grow very well in a greenhouse for most seasons. Some particularly suitable varieties:

• 'Reine de Mai' (May Queen): fast-growing, bolt-resistant, ideal for spring and autumn sowing
• 'Forellenschluss' (or "trout"): a beautiful Austrian variety with red spots, excellent cold tolerance
• 'Merveille des Quatre Saisons' (Marvel of Four Seasons): its name says it all. It adapts to all seasons, and its red leaves also make it a beautiful ornamental plant in a greenhouse

🌿 Cut-and-come-again leaves (or mesclun)

This is our favorite for continuous greenhouse production all year round. The idea is simple: you cut the outer leaves as you need them, and the plant regrows. This is known as "cut-and-come-again" harvesting.

Among the best options:

• Rocket: pungent, fast-growing (20 to 25 days), good cold resistance
• Perpetual spinach: not strictly a lettuce, but perfect for mixed greens
• Curly lettuce 'Lollo Rossa' or 'Lollo Bionda': pretty, productive, tolerant of moderate heat
• Corn salad (Mâche): excellent for autumn and winter sowing, very hardy

❄️ Winter-specific varieties

In winter, variety choice is crucial. Some lettuces have been specifically selected to withstand negative temperatures. In a greenhouse, they do even better because they don't experience direct frost.

• 'Valdor': a particularly robust butterhead lettuce, ideal between October and March
• 'Rouge d'Hiver' (Winter Red): an old, very hardy French variety, with elongated reddish leaves
• 'Grenoble Rouge': dense, flavorful, excellent performance in cold conditions

🧑🌾 A practical tip we often give: always mix several varieties in your greenhouse. You'll have a more diverse harvest, better resilience to unforeseen events, and frankly, a much more visually appealing vegetable patch.

📅 Lettuce sowing calendar in a greenhouse: month by month

This is probably the most practical section of this guide. Here is a realistic and detailed calendar for growing lettuce in a greenhouse all year round, designed for French climatic conditions.

⚠️ Warning: this calendar is valid for a properly installed and oriented polycarbonate greenhouse. If your greenhouse is poorly exposed or poorly insulated, the margins for maneuver will be smaller, especially in winter.

🛠️ Preparing your greenhouse for growing lettuce: the basics

Before planting a single seed, there are a few essential preparation steps. Beginners in a hurry often skip them, and that's almost always where problems begin. 😅

🌍 Soil or substrate quality

Lettuce has a rather superficial root system. It doesn't need deep soil, but it needs light, well-drained soil rich in organic matter.

Some concrete options:

• Growing trays: ideal in a greenhouse because they allow total control of the substrate. A mix of 50% potting soil + 30% well-rotted compost + 20% coarse sand works very well for lettuce.
• Open ground: possible if the soil is well-loosened. Add compost to the surface (5 to 8 cm) and lightly work it into the surface without deep digging.
• Beds or planters: practical for small greenhouses, they also allow for multiple growing levels.

By the way, if you're wondering how to optimize space in your greenhouse, you'll find valuable advice in our article on the 10 essential plants for starting in a greenhouse.

💧 Watering: neither too much, nor too little

This is one of the most poorly managed parameters by beginners. Lettuce likes humidity, but it hates having its feet in water. Constantly soggy soil promotes the development of rot and fungal diseases, especially root rot and downy mildew.

Some rules to remember:

• Water preferably in the morning, so the foliage can dry during the day
• Check the soil by pushing your finger about 2 cm deep: if it's still damp, you don't need to water
• In summer, needs are greater (sometimes daily). In winter, space out watering to 2 or 3 times a week
• Avoid watering directly onto the leaves, especially in humid conditions

💡 A tip we often give: install a drip irrigation system in your greenhouse. It's a modest investment that truly changes life, especially in summer when lettuce can suffer quickly.

🌡️ Managing greenhouse temperature: the key to success

Lettuce ideally grows between 10°C and 22°C. Outside these ranges, problems begin.

In winter: if temperatures drop below 5°C at night, consider a winter fleece cover inside the greenhouse, or a small thermostatically controlled heater. A 6mm polycarbonate greenhouse retains heat much better than a 4mm model, and this is often the difference between a successful crop and a disappointing harvest in January.

In summer: this is the other extreme. Above 28°C, lettuce tends to "bolt," meaning it prematurely goes to flower, making the leaves bitter and unusable. To avoid this:

• Open windows and doors first thing in the morning
• Install a shade cloth over the greenhouse roof (30 to 50% shade is sufficient)
• Water regularly to maintain a cool temperature at soil level

🌱 Sowing lettuce in a greenhouse: how to proceed step by step

Now, let's get down to business. Here's the method we recommend for successful sowing, whether you're a complete beginner or an experienced gardener. 🧑🌾

Step 1: Prepare your sowing container 🪴

Fill a seed tray or a small container with special seed compost (fine, light, not too rich in nutrients). Lightly tamp and moisten before sowing. A common mistake is to sow in overly rich compost: young roots need to "seek out" food to develop properly.

Step 2: Sow on the surface 🌱

Lettuce seeds are photosensitive: they need light to germinate. So, never bury them! Simply place them on the surface, then press lightly with the palm of your hand to ensure contact with the substrate. A very light covering of fine sand can help maintain humidity without blocking the light.

Step 3: Maintain humidity and warmth 🌡️

Cover the tray with a transparent lid or plastic film. The ideal germination temperature is between 15°C and 20°C. Below 10°C, germination can take 2 to 3 weeks (or even fail). Above 25°C, the germination rate also drops.

Step 4: Remove the cover as soon as seedlings emerge ☀️

As soon as you see the first small leaves appear (usually 5 to 10 days depending on the season), remove the cover and place the tray in a well-lit area. At this stage, excessive humidity becomes an enemy: young plants can succumb to damping-off if the substrate remains too wet.

Step 5: Transplanting 🌿

When the plants have 2 to 4 true leaves (count about 3 to 4 weeks after emergence), it's time to transplant them to their final location. Space them 20 to 25 cm apart in the row, and 30 cm between rows. Don't plant too deep: the crown (the base of the leaves) should remain above the soil.

💡 The most common mistakes in growing lettuce in a greenhouse

We have supported many gardeners in their greenhouse adventures, and we often see the same mistakes recurring. Here are the main ones, with solutions. 🔍

❌ Mistake #1: sowing too densely

This is the number one mistake. People think "the denser, the more lettuce we'll have," but in reality, overcrowded plants compete, become leggy, and are much more susceptible to diseases. Always respect the recommended spacing.

❌ Mistake #2: not ventilating during the day

A closed greenhouse in full sun can reach insane temperatures in a very short time (40°C or more in some cases). This is destructive for lettuce. Open the greenhouse first thing in the morning as soon as the sun rises, and close it in the late afternoon to retain heat.

❌ Mistake #3: watering in the late afternoon

Nighttime humidity combined with cool temperatures is the ideal breeding ground for downy mildew and botrytis. Always water in the morning so that the foliage can dry during the day.

❌ Mistake #4: neglecting the soil between two crops

Between two batches of lettuce, take the time to weed, amend the soil with compost, and possibly let it rest for a few days. Exhausted soil yields flavorless lettuce.

❌ Mistake #5: waiting for lettuce to be "too big"

Lettuce should be harvested young! Overripe lettuce will bolt (go to seed). Harvest as soon as the head is well-formed (or the leaves are well-developed for cut-and-come-again varieties), without waiting for it to be "perfect."

🔥 Growing lettuce in a greenhouse in winter: is it really possible?

Yes. And it's even simpler than you might think. 🌨️

In France, winters vary by region. In Brittany, temperatures rarely drop below -5°C. In the North-East, they can reach -15°C. Your winter strategy therefore depends heavily on your geographical location and the quality of your greenhouse.

Here's what we specifically recommend for growing lettuce in a greenhouse in winter under good conditions:

🌡️ Choose a 6mm polycarbonate greenhouse: the thermal insulation is significantly superior to that of a 4mm model. According to ADEME data, good insulation can reduce heating needs by 25 to 40%, which is considerable over the winter. This is also one of the reasons why we offer this choice on models like L'Intemporelle, our polycarbonate tunnel greenhouse available in 4mm and 6mm depending on your climatic needs.

🧣 Add a fleece cover inside: even in a greenhouse, a P30 fleece placed directly over the lettuce can gain an additional 2 to 3°C at night. This is often the difference between a successful harvest and a frozen one.

💡 Opt for supplementary heating during extreme cold: a small thermostatically controlled fan heater (set to a minimum of 5°C) is enough to protect your crops without skyrocketing the electricity bill. There's no need to heat to 18°C: winter lettuce grows (slowly, admittedly) from 5°C upwards.

🪟 Limit ventilation in winter: unlike in summer, restrict openings in mid-winter. Open slightly in the middle of the day if the weather is mild and sunny, and close before 4 pm to retain the accumulated heat.

And most importantly: be patient. In winter, growth is slow. A plant that grows in 3 weeks in April might take 6 to 8 weeks in January. This isn't a problem, it's just the reality of nature. 🌿

☀️ Managing the greenhouse in summer for lettuce: preventing bolting

Summer is paradoxically the most difficult period for growing lettuce in a greenhouse. Intense heat can make the leaves bitter, cause premature bolting, and render your plants practically unusable within a few days.

Here are the strategies that really work:

🌑 Shading: this is the number one solution. A 40-50% shade net placed on the greenhouse roof can reduce the internal temperature by 5 to 8°C. This is considerable. Some gardeners use reflective white tarpaulins with similar results.

💨 Maximum ventilation: in summer, open everything that can be opened. Doors, roof vents, side vents if your greenhouse is equipped with them. Air must circulate constantly.

🌊 Increased watering frequency: moist soil evaporates and cools. In mid-summer, daily watering (or even twice a day for young plants) is not excessive.

📍 Stagger your sowings: in July-August, prefer sowing in the late afternoon or cool morning. Avoid exposing seed trays to full sun.

🌿 Focus on resistant varieties: some lettuces have been selected for their resistance to bolting. 'Batavia Dorée de Printemps', 'Craquerelle du Midi' or 'Australienne' are particularly suited to warm periods.

🥗 Optimize your harvests: the "cut-and-come-again" technique and rotations

If you want to never run out of fresh lettuce in your kitchen, there are two techniques you absolutely must master. 📈

✂️ "Cut-and-come-again" harvesting

For leafy varieties (arugula, Lollo Rosso, endive, spinach), do not cut the entire plant. Harvest only the outer leaves, leaving the heart and at least 3 to 4 inner leaves. The plant will continue to produce for several weeks, or even several months depending on the season.

A single arugula plant treated this way can provide you with leaves for 2 to 3 months. This is an exceptional quality/yield ratio for such a small area. 🌱

🔄 Sowing rotations

Rather than sowing all at once, sow in small quantities every 2 to 3 weeks. This is what professional market gardeners call "staggered sowing." The result: a continuous harvest, without a surplus all at once and a shortage the following week.

Concretely, it looks like this:

• Week 1: first sowing of 10 plants
• Week 3: second sowing of 10 plants
• Week 5: third sowing, etc.

With 3 to 4 batches in rotation, you always have some mature lettuce somewhere in the greenhouse. 💡

🌍 Crop rotation

To avoid exhausting the soil and preventing the accumulation of diseases, do not replant lettuce in the same spot indefinitely. Alternate with other plant families: radishes, carrots, onions, basil... Before planting lettuce in the same spot again, allow at least 2 to 3 crop cycles of other plants to pass.

🪴 Which greenhouse to choose for growing lettuce all year round?

This is a question we are asked regularly, and the answer depends on several factors: your available space, your region, your production ambitions, and of course your budget. 🌍

At AtmoSerre, we have designed our polycarbonate greenhouses to suit all types of gardeners. Here are the truly important criteria for growing lettuce in a greenhouse all year round:

📐 Surface area: for a family of 4 people wishing regular lettuce production, a greenhouse of 12 to 18 m² is a comfortable minimum. Below that, you can produce, but you will quickly be limited if you wish to vary your crops.

🏗️ Height: a tall greenhouse (1.8 m minimum) is more comfortable to work in and promotes better air circulation. Avoid overly low greenhouses that create "pockets" of heat in summer.

🌡️ Polycarbonate thickness: for year-round cultivation, 6 mm polycarbonate is significantly preferable. It offers much better thermal insulation than 4 mm, which is particularly crucial during winter nights.

💨 Integrated ventilation: check that your greenhouse has at least one roof vent or side vents. This is essential for summer.

If you want to explore all our options, you can consult our garden greenhouse collection, where you will find models for all profiles and garden configurations.

🌿 Fertilizing greenhouse lettuce: what you need to know

Lettuce are short-cycle plants: they don't need a lot of fertilization. Too much fertilizer, especially nitrogen, can even have negative effects: overly tender foliage, nitrate accumulation, increased susceptibility to diseases.

Here's what works well in practice:

🌱 Before planting: incorporate well-rotted compost (5 to 10 cm) into the soil. This is the best "base fertilizer" for lettuce. No need for chemical fertilizers if your compost is of good quality.

💧 During cultivation: if your plants appear pale or are growing slowly, a diluted application of liquid seaweed fertilizer (once every 2 weeks) can help, especially in winter when natural soil decomposition is slower.

❌ What to avoid: classic granular fertilizers with high nitrogen content. They promote overly rapid growth, at the expense of flavor and disease resistance.

🧑🌾 A little field secret: comfrey leaves macerated in water (comfrey slurry) make a natural liquid fertilizer, rich in potassium and trace elements, particularly suitable for lettuce. Let it steep for 2 weeks, dilute to 1/10, and water directly at the base of the plants.

🐛 Diseases and pests in greenhouses: how to protect your lettuce

Even in a greenhouse, lettuce is not entirely safe. Here are the main enemies and natural solutions that truly work. 🔬

🍄 Downy Mildew (Bremia lactucae)

This is the number one disease of greenhouse lettuce. It manifests as yellow spots on the upper side of the leaves, with grayish-white down on the underside. It thrives in humid and cool conditions, especially in autumn and spring.

Solutions:

• Improve ventilation at the first signs
• Avoid wet foliage
• Use resistant varieties (look for "Bl" followed by a number on seed packets)
• As a preventative treatment, Bordeaux mixture at a low dose can help, but use it sparingly

🐛 Aphids

They attack young leaves and stems, and can multiply very quickly in the warm conditions of a greenhouse. Their presence weakens plants and can transmit viruses.

Natural solutions:

• Diluted black soap (1 tablespoon in 1 liter of water) applied as a spray
• Introduction of ladybugs or lacewings (available from auxiliary suppliers)
• Nettle manure as a preventive spray

🐌 Slugs

Less common in greenhouses than outdoors, they can still show up, especially in humid weather. A few metaldehyde pellets strategically placed (but out of reach of children and animals) or wood ash barriers around the beds work well.

🔴 Mites (red spiders)

In summer, in hot and dry weather, red spiders can invade your lettuces. Symptom: leaves dotted with tiny spots, slight discoloration. A spray of fresh water (they hate humidity) and regular watering are often enough to control them.

🧑🌾 Feedback: what we observe with our customers

At AtmoSerre, we are fortunate to be in regular contact with our customers, and the feedback on growing lettuce in greenhouses is unanimous: it is the first crop that everyone recommends to beginners. 🌿

What they often tell us:

💬 "The first time I harvested lettuce in the middle of January, I understood why I had invested in a greenhouse."

💬 "I didn't think it was that simple. Now we have fresh lettuce almost all year round, and my kids love to pick it."

💬 "The mistake I made at the beginning was overwatering. Once I understood the right rhythm, the results were immediate."

This feedback confirms what we have thought from the beginning: the garden greenhouse is not a luxury for enthusiasts. It is a practical, accessible tool that truly transforms the way we eat and garden.

🌍 Data to know about lettuce consumption in France

Some figures to measure the interest of producing your own:

📊 According to the FranceAgriMer website (official source of the Ministry of Agriculture), France produces approximately 400,000 tons of lettuce per year, but consumes much more, with a strong dependence on imports during the winter period.

📊 The average price of a lettuce in supermarkets varies between €0.80 and €2.50 depending on the season and variety. In winter, prices can climb up to €3 or €4 for an organic lettuce.

📊 With a 12 m² greenhouse, by cultivating lettuce on 6 m² in rotation, you can produce between 3 and 5 lettuces per week during peak season, which represents an annual saving of €200 to €400 just on this item.

This is far from negligible, especially if you add tomatoes, cucumbers, aromatic herbs, and other possible crops in the same greenhouse. 💡

❓ FAQ: Your questions about growing lettuce in a greenhouse

Q: Can you grow lettuce in an unheated greenhouse in winter?

Yes, absolutely, especially in regions with mild winters (Brittany, Mediterranean, Atlantic coast). In colder regions, a simple forcing cover inside the greenhouse, possibly combined with supplementary heating set to a minimum of 5°C, is sufficient to maintain crops. Winter varieties such as 'Valdor' or lamb's lettuce can withstand temperatures close to 0°C.

Q: How long does it take from sowing to harvesting lettuce in a greenhouse?

It depends on the season and the variety. In summer, allow 4 to 6 weeks between sowing and harvesting. In winter, growth slows down and it can sometimes take 8 to 12 weeks. For cut-and-come-again varieties (rocket, lollo), the first harvest can take place in 3 to 4 weeks.

Q: What is the best orientation for a greenhouse dedicated to lettuce?

A greenhouse oriented north-south allows maximum sun exposure in all seasons. However, an east-west orientation favors morning exposure, often preferable in winter to quickly warm up the greenhouse after night. In all cases, avoid areas shaded by trees or buildings.

Q: Do greenhouse lettuces taste good compared to commercially grown ones?

Yes, and often much better. Greenhouse-grown lettuces grow at their own pace, without forcing, without chemical treatments (if you don't use any), and are harvested fresh. Their taste is generally more pronounced, their texture crispier, and they keep longer after harvest.

Q: Can you grow lettuce in a greenhouse at the same time as other vegetables?

Yes, it's even recommended! Lettuces pair very well with tomatoes (they benefit from their shade in summer), carrots (they occupy different spaces), radishes (very short cycle, good companion) and aromatic herbs. To learn more about companion planting in a greenhouse, read our dedicated article: Growing tomatoes in a polycarbonate greenhouse: complete guide 2026!

Q: How much lettuce can you produce with a 6 m² greenhouse?

With 6 m², by cultivating lettuce over the entire surface in rotation, you can produce about 2 to 3 lettuces per week during peak production, or about a hundred lettuces per year. This is quite sufficient for a family of 2 to 3 people for fresh green vegetables.

🌱 Conclusion: get started, the lettuce won't wait!

You understand: growing lettuce in a greenhouse all year round is within everyone's reach. No need to be an expert, no need for a huge greenhouse, no need for sophisticated equipment. All you need is a little method, the right varieties, and a correctly installed and oriented greenhouse.

What we observe at AtmoSerre is that gardeners who start growing lettuce in a greenhouse never go back. 🥗 They discover the pleasure of eating fresh vegetables they have grown themselves, of controlling their diet, of gardening all year round regardless of the weather.

If you are considering equipping yourself or if you are looking for the ideal greenhouse to start your market gardening adventure, we invite you to explore our garden greenhouses: models designed for all gardens, all regions of France, and all levels of practice.

🌿 Tomorrow's lettuce is already growing in your greenhouse. All you have to do is sow it.