Greenhouse Growing Calendar: What to Plant Year-Round?

By the AtmoSerre team

There’s a question we often hear, and frankly it’s a legitimate one: "Can I use my greenhouse all year round or only in spring?" The short answer is yes, absolutely all year. But the real answer, the one that will change your gardening life, is that a well-used polycarbonate greenhouse means 12 months of active cultivation, with harvests almost without interruption.

At AtmoSerre, we support hundreds of enthusiasts each year in setting up their first greenhouse. And the most common mistake we see? People who leave their greenhouse empty from November to March, convinced that there’s "nothing to do." Spoiler: there’s always something to do. 🌱

This guide is your complete greenhouse growing calendar, month by month, crop by crop. Whether you’re a beginner or have been gardening for ten years, you'll find concrete ideas, possibilities you might not have considered, and above all, a real logic of rotation and planning. Because a garden greenhouse is not just protection from the rain. It’s a production tool in its own right.

🌡️ Understand the greenhouse microclimate before planting anything

Before going into detail month by month, it's essential to lay a foundation: your greenhouse does not have the same climate as your garden. And that's precisely what makes it so valuable.

A polycarbonate greenhouse, even unheated, can be 5 to 10°C warmer than outside during the day. At night, the difference narrows, but frost protection remains real with a well-insulated 6mm panel. With simple supplementary heating or a well-designed thermal mass (black water barrels that absorb daytime heat), you can maintain positive temperatures even in very cold weather.

What this concretely changes for your greenhouse growing calendar:

• 🌱 You can start your seedlings 6 to 8 weeks earlier than outdoors
• ❄️ You can extend your harvests until December or January
• 🔥 You can grow Mediterranean species in regions where they wouldn't survive the winter
• 📈 You significantly increase your overall yield throughout the year

According to INRAE data, an unheated greenhouse, on average, allows you to extend the growing season by 4 to 6 months compared to outdoor cultivation. With minimal heating, you can easily achieve 12 continuous months.

That said, greenhouse management is something you learn. Ventilation, watering, humidity… these are all parameters that change compared to a traditional garden. If you're a beginner, we've written a comprehensive guide on How to Start Seeds in a Greenhouse: The Complete Beginner's Guide! that will give you all the basics before you begin.

📅 The Monthly Greenhouse Growing Calendar

🌨️ January: the greenhouse is not on holiday

Many gardeners see January as a dead month. In a greenhouse, it's quite the opposite. It's even the ideal month to prepare for the coming season.

What you can grow in January:

• 🥬 Lamb's lettuce, spinach, arugula: these crops are perfectly cold-hardy and grow slowly but surely. Sown in autumn, they are ready to harvest now.
• 🧅 Spring onions and shallots: you can start sowing in trays from mid-January under warm cover.
• 🌿 Aromatic herbs: thyme, rosemary, chives do very well in an unheated greenhouse.
• 🌱 First tomato seedlings: if your greenhouse has a mini-heater or an indoor seed propagator, early January is possible for early varieties.

What you mainly do in January: This is the month for cleaning and planning. You disinfect trays, prepare substrates, and place seed orders. A well-organized gardener in January is a gardener who harvests early in May.

💡 Field tip: place dark water barrels in your greenhouse. They absorb solar heat during the day and release it at night, creating a natural thermal buffer. Simple, free, and incredibly effective.

❄️ February: sowings slowly resume

February is the month when enthusiasts start getting busy. Light gradually returns, days get longer, and in a greenhouse, you quickly feel it.

What you can sow in February:

• 🍅 Tomatoes: in trays or pots, place in the warmest part of the greenhouse. Aim for germination around 18-22°C.
• 🫑 Peppers and eggplants: these long-season species should be sown early. February is the right time.
• 🥒 Cucumbers: for a May harvest, sow in February in a heated greenhouse.
• 🌿 Basil: indoors in a heated greenhouse, on a well-lit windowsill.
• 🥗 Head lettuce: sow in trays, transplant in March.

What you transplant in February: Onions sown in January can already be pricked out into modules. Spinach and lamb's lettuce planted in autumn can be continuously harvested.

February is also when you think about replacing your accessories: if your irrigation system broke down last year, now is the time to anticipate it, before the busy restart in March.

🌸 March: the garden awakens

March is often gardeners' favorite month. Energy returns, seedlings explode, and for the first time of the year, it feels like real production is happening.

What you sow in March:

• 🍅 Tomatoes (2nd round to stagger harvests)
• 🥕 Carrots: in a greenhouse, they can be sown directly in the ground from March, protected from late frosts
• 🥦 Cauliflowers and broccolis: in trays, for outdoor planting in April-May
• 🌽 Courgettes (Zucchini): in individual pots, they dislike traumatic transplanting
• 🫛 Beans: first sowings possible if the greenhouse is well-tempered
• 🌼 Annual flowers: nasturtiums, zinnias, cosmos… which will also help attract pollinators

What you transplant in March: Tomatoes and peppers sown in January-February often reach 10-15 cm. Transplant them into individual 10-12 cm pots. This is a key moment: a damaged root now means a weakened plant for the entire summer.

🌡️ Beware of March nights: late frosts down to -5°C are still possible in many French regions. Your greenhouse protects, but if you have a 4mm greenhouse in a cold region, keep a horticultural fleece handy to double the protection on critical nights.

This is also one of the reasons why we recommend 6mm polycarbonate for users who want true four-season growing without constraints. Our model L'Intemporelle is available in 4 and 6mm, precisely to adapt to all climatic profiles.

🌷 April: the main season begins

April is the turning point. Outside, nature is waking up. In your greenhouse, things have been growing for weeks. This is where you see the real benefit of having planned early.

What to plant in April:

• 🍅 Tomatoes: final transplanting into the greenhouse if nights remain above 10°C
• 🥒 Cucumbers: planting directly in the greenhouse soil or in containers
• 🫑 Peppers and eggplants: final placement
• 🍓 Strawberries: planting runners or potted plants, first harvests expected in June
• 🫘 Green beans: direct sowing in the greenhouse soil

What you can already harvest in April:

• 🥗 Lettuce sown in February
• 🌿 Aromatic herbs continuously
• 🥬 Spinach from the previous autumn (end of cycle)
• 🌱 Radishes sown in March (short cycle of 3-4 weeks in a greenhouse)

April is also the month for serious ventilation. Daytime temperatures can reach 25-30°C in a closed greenhouse. If you don't have roof vents or side vents, temperatures quickly become problematic. A simple oversight in the morning, and you'll find your lettuce plants scorched by noon.

☀️ May: warmth and maximum productivity

In May, a well-managed greenhouse resembles a miniature Garden of Eden. Everything grows, everything greens, and the first real harvests arrive.

What to sow in May:

• 🌽 Sweet corn (for a late July harvest)
• 🌶️ Hot peppers (long-maturing varieties)
• 🍈 Melons: in May, conditions are perfect for their start
• 🫛 Climbing beans (2nd sowing to stagger)

What to harvest in May:

• 🥒 First courgettes (zucchini)
• 🍓 First strawberries if planted early
• 🥗 Salads continuously
• 🌿 Chives, parsley, basil in abundance

💡 Field tip: in May, ventilate morning and evening, and leave open during the day if the weather permits. This is the first real test of your ventilation management. A greenhouse that overheats in May means a compromised tomato harvest later.

🌞 June-July: peak season

These two months are the pinnacle of greenhouse cultivation. The heat is present, light is maximal, and summer crops are producing at full capacity.

The stars of June-July in the greenhouse:

• 🍅 Tomatoes: first harvests for early varieties from late June
• 🥒 Cucumbers: intense production, harvest every 2-3 days
• 🫑 Peppers: beginning of reddening for red varieties
• 🍈 Melons: manual pollination if no insects, fruits visibly growing
• 🌶️ Peppers starting to turn color
• 🍓 Strawberries at peak production

Key actions in June-July:

• Stake and prune tomatoes weekly (remove suckers)
• Water regularly, preferably in the morning. Avoid wetting the foliage
• Watch out for red spider mites which thrive in the dry heat of greenhouses in summer
• Mulch the soil to conserve moisture and reduce watering
• Open as much as possible: side panels, roof vents, everything must be ventilated

In July, also remember to sow your autumn crops to have something to harvest in September-October. Planning is the key to year-round greenhouse cultivation.

🍂 August: preparing for autumn without stopping summer

August is the month of transition. Summer is still in full swing, but it's already time to think about what comes next.

What to harvest in August:

• 🍅 Tomatoes at peak production
• 🥒 Cucumbers and zucchini
• 🍈 Melons and watermelons (if started early)
• 🌶️ Hot and bell peppers
• 🫘 Green beans

What to sow in August for autumn:

• 🥬 Spinach: 6-8 week cycle, harvest in October
• 🥗 Lamb's lettuce: sow from mid-August for a harvest from November to January
• 🧅 White onions: tray sowing
• 🥦 Kohlrabi, winter radish: short cycles, perfect for filling space
• 🌿 Flat-leaf parsley: very resistant to the first cold snaps in a greenhouse

August is also the time to think about serious fertilizing. After several months of intensive cultivation, the growing media are depleted. Adding compost or liquid fertilizer every two weeks makes a real difference to the quality of the last summer harvests.

🍁 September: the extended beautiful season

September is often the month when outdoor gardeners start putting away their tools. In a greenhouse, production is still in full swing.

What to do in September:

• 🍅 Continue harvesting tomatoes until the first frosts (often October or November depending on the region)
• 🥒 Cucumbers are still producing well until mid-September
• 🥗 New lettuces sown in August are ready for transplanting
• 🌿 Cut aromatic herbs and dry or freeze them for winter

What to plant in September:

• 🧄 Garlic: plant from September for a harvest in June of the following year
• 🧅 Spring onions: plant in a greenhouse for an early harvest
• 🫛 Peas: cold-resistant varieties, sow in a greenhouse for a harvest in November-December
• 🥬 Lamb's lettuce and spinach: transplant seedlings from August

💡 In September, the light decreases. It's imperceptible at first, but plants feel it. Tomatoes take longer to ripen. Adjust your expectations and make use of green tomatoes: green tomato jam, chutney... there are a thousand ways to waste nothing.

🌧️ October: the great transition

October marks the beginning of true winter work. Summer crops are nearing the end of their life, and the transition must be managed without leaving the greenhouse empty.

What to still harvest in October:

• 🍅 Green tomatoes to ripen on a windowsill or to cook
• 🫑 Bell and hot peppers to dry or freeze
• 🥬 The first harvests of spinach and lamb's lettuce
• 🧄 Garlic planted last month begins to show its first shoots

What to plant in October:

• 🌸 Spring bulbs: tulips, daffodils, hyacinths in pots for advanced flowering from February-March in a greenhouse
• 🥬 Spinach: last possible sowing before the light gets too low
• 🥗 Lamb's lettuce: it loves the cold, it's its season
• 🌿 Chives in pots: they easily grow back in a greenhouse and produce all winter

This is also a good time to deep clean the greenhouse after the summer crops. Remove plants at the end of their life, weed, amend the soil with well-rotted compost. A soil prepared in October means a greenhouse that will take off in spring.

❄️ November: tranquil winter gardening

November has a bad reputation. It's grey, rainy, and the days are short. And yet, in a greenhouse, really interesting things happen.

What to grow in November:

• 🥬 Lamb's lettuce: discreet and steady producer, it requires little and gives a lot
• 🌿 Spinach: slow but real growth, harvested leaf by leaf
• 🧅 Chives and parsley: they slow down but don't die
• 🥗 Winter lettuces (like 'Merveille des 4 Saisons'): cold-resistant, they grow slowly but surely
• 🌱 Garden cress: ultra-short cycle (3 weeks), ideal for maintaining activity in the greenhouse

What to prepare in November:

• Sowing plan for January-February
• Seed orders for the next season (the best varieties sell out quickly)
• Review of the greenhouse structure before the strong winter winds

If you have an AtmoSerre greenhouse, you know it's designed to withstand winds up to 180 km/h and snow loads up to 90 cm. But a small annual check of the fastenings and panels before winter is always a good habit.

🎄 December: the greenhouse at rest... but not empty

December is the quietest month. But even then, a greenhouse doesn't completely sleep.

What to grow in December:

• 🥬 Lamb's lettuce and cress: they continue to produce even when night temperatures hover around 0°C
• 🌿 Hardy aromatic herbs: thyme, rosemary, sage survive without problems
• 🧄 Garlic planted in September begins to establish well
• 🌱 Shoots and microgreens: on a simple light tray, radish, sunflower, or pea sprouts can be produced in 7-10 days. No cold needed.

What to do in December:

• Seriously plan for season N+1
• Order your seeds (catalogs often open in November-December)
• Consider adding a min/max thermometer if you haven't already: essential for monitoring cold nights
• Look at offers on accessories: growing trays, irrigation systems... prices are often more attractive in winter

📊 Summary Table of Greenhouse Growing Calendar

🌿 Essential Year-Round Greenhouse Crops

Some plants are truly made for the greenhouse. Here are those that deserve a permanent place in your schedule.

🍅 Tomatoes: the queen of the greenhouse

No need for an introduction. But what's often forgotten is that certain tomato varieties can produce until December in a greenhouse if heat is managed well. Cherry varieties like 'Sweet Million' or 'Supersweet 100' are particularly prolific. By sowing them in early February, you can have fruit from June to November.

🥒 Cucumbers: prolific producers in the greenhouse

Cucumbers are one of the most profitable crops in a greenhouse. A single well-managed plant can yield 20 to 30 fruits during the season. They love warmth (no less than 15°C at night), humidity, and regular staking. In a greenhouse, they are also protected from outdoor blight.

🍓 Strawberries: fruit almost all year round

By playing with varieties (everbearing vs. June-bearing) and greenhouse temperatures, it is entirely possible to have strawberries from March to December. Everbearing varieties like 'Mara des Bois' or 'Charlotte' are ideal for this purpose.

🌿 Aromatic Herbs: the perma-producing garden

Basil, parsley, chives, coriander, tarragon... In a greenhouse, they grow almost all year round with minimal maintenance. Basil needs warmth (sow it from March), but parsley and chives get through winter without a hitch.

🥗 Salads: the hunger-buster vegetable

Between summer crops, salads perfectly fill empty spaces. Their short cycle (6 to 8 weeks in a greenhouse) allows them to be squeezed into the calendar everywhere. Grow them in tight rows, harvest leaf by leaf ('cut and come again'), and they renew themselves.

🛠️ The Right Accessories for Year-Round Greenhouse Cultivation

Having a beautiful greenhouse is good. Equipping it intelligently is better. Here's what truly makes a difference in 12-month cultivation.

🌡️ The min/max thermometer Essential. Without it, you're navigating blindly. It shows you the extreme temperatures of night and day. You'll know exactly if your tomatoes have suffered thermal stress or if your seedlings risk freezing.

💧 The irrigation system Especially in summer, where forgetting to water can kill a crop in a few hours. A programmable drip system frees you from constraints and maintains constant humidity.

🪴 Wooden growing boxes They allow you to perfectly control the composition of the substrate according to each crop. You use a soil/compost/perlite mix for tomatoes, a lighter substrate for salads, etc. And they keep the roots nicely warm.

☁️ The shade net In summer, greenhouse temperatures can exceed 40°C on heatwave days. A shade net placed on the south-facing panels reduces the temperature by 5 to 8°C without depriving plants of light.

🌿 The plant tying kit For staking tomatoes, cucumbers, melons... without injuring the stems. Essential for well-managed tall crops.

All these accessories are available directly on AtmoSerre, designed to adapt to our greenhouse models.

🌍 Adapt Your Calendar to Your Region

France is a country of climatic contrasts, and your greenhouse growing calendar must take this into account. What works in Provence does not directly apply in Alsace.

🌊 Oceanic regions (Brittany, Normandy, Atlantic coast) Mild but humid winters. The enemy is not the cold, it's humidity and lack of light. Ventilation is favored even in winter to avoid fungal diseases. Sowing starts in February rather than January.

🏔️ Continental and mountainous regions (Alsace, Auvergne, Alps) Cold and contrasting winters. Here, 6mm polycarbonate is really recommended. Sowing starts later (March for many vegetables), but hot summers compensate with good productivity.

☀️ Mediterranean regions (PACA, Languedoc, Corsica) The challenge is not the cold in winter, it's the heat in summer. You need to shade in July-August and take advantage of the mild winter to continuously grow species that freeze everywhere else.

🌱 Semi-continental regions (Ile-de-France, Centre) Intermediate profile. Greenhouses work very well with 4mm for spring-summer use, and 6mm for true winter cultivation. This is the most common profile of our clientele.

If you are still choosing your greenhouse, take a look at our complete collection of garden greenhouses to find the model suited to your region and available space.

🔄 Crop Rotation in the Greenhouse: An Often Neglected Point

We repeat it every year, and yet... Growing the same thing in the same place two years in a row in a greenhouse is a sure way to have problems. Diseases settle in the soil, pests reproduce, and crop quality drops.

The basic rules of greenhouse rotation:

• 🍅 Solanaceae (tomatoes, peppers, eggplants): no more than 2 consecutive years in the same location
• 🥒 Cucurbits (cucumbers, zucchini, melons): same
• 🥬 Brassicaceae (cabbages, arugula): ideally not after solanaceae
• 🌿 Legumes (beans, peas): excellent for fertilizing the soil between two heavy crops

In practice, space is limited in a greenhouse. But even a simple side-swap (tomatoes on the left one year, on the right the next) makes a real difference. And partially renewing the soil every 2-3 years is a guarantee of lasting productivity.

❓ FAQ: Your Questions About the Greenhouse Growing Calendar

Can you really grow in a greenhouse all year round without heating? Yes, in the vast majority of French regions. A 6mm polycarbonate greenhouse protects against frost down to about -8 to -10°C under normal conditions. You can grow cold-resistant vegetables (lamb's lettuce, spinach, garlic, arugula) all winter without any heating. For warm crops (tomatoes, basil), a small auxiliary heater is sufficient.

When should you start sowing tomatoes in a greenhouse? That depends on your equipment. With a heated greenhouse at a minimum of 18°C, you can sow from mid-January. Without heating, it's better to wait until mid-February to early March depending on your region. The important thing is that the seedlings sprout at a good temperature and do not suffer from the cold during the first nights.

How to prevent diseases in the greenhouse in winter? Humidity is the main enemy in winter. Ventilate even in cold weather (open for 15 minutes in the morning if possible), water preferably in the morning so that excess dries during the day, and avoid wetting the foliage. Good spacing between plants also helps air circulation.

Is a tunnel greenhouse as effective as a straight greenhouse for year-round cultivation? Yes, in most cases. A well-insulated tunnel greenhouse (6mm polycarbonate) is excellent for 4-season cultivation. It is even sometimes more thermally efficient due to its rounded volume which limits thermal bridges. Our L'Intemporelle model is precisely a tunnel greenhouse designed for this intensive year-round use.

What is the minimum greenhouse area for year-round cultivation? A minimum of 6 m² (2x3 meters) is generally recommended to have enough space for proper rotation and varied crops. Below that, space quickly becomes an issue. But even 6 m², well organized, can produce an impressive amount of vegetables. We have written a complete article on the 10 essential plants for starting in a greenhouse which will help you make the right choices if you are starting with a small area.

Can melons be grown in a greenhouse in France? Absolutely, and it's even one of the great pleasures of greenhouse gardening! Melons need heat (20-25°C minimum during the day), good pollination, and controlled watering. In an unheated greenhouse, you sow in May and harvest in August. In a heated greenhouse, you can sow from March for a July harvest.

🌱 Conclusion: your greenhouse deserves to be active 365 days a year

A well-structured greenhouse growing calendar is the difference between a greenhouse that is used 4 months a year and a greenhouse that produces continuously. It's not a question of extraordinary equipment or esoteric know-how. It's a question of planning, observation, and small habits that gradually take hold.

The first year, you make mistakes. That's normal. You forget to sow autumn vegetables in July. You sow tomatoes too late. You don't ventilate enough in May. But the following year, you adjust. And after two or three seasons, greenhouse cultivation becomes a true second nature.

If you don't have your greenhouse yet, it might be the best time to think about it. On AtmoSerre, we offer polycarbonate greenhouses designed to last, with a warranty of up to 10 years and a structure capable of standing up to the elements. Because a greenhouse should accompany you for decades, not just a few seasons.

🌿 Get started, and happy harvests all year round!