What to plant in a greenhouse in summer? The complete 2026 guide!

Summer is coming, temperatures are rising, and your polycarbonate greenhouse is transforming into a true growth engine. But here's the real question every gardener eventually asks: what to plant in a greenhouse in summer to make the most of this golden season? Because a greenhouse in summer is an incredible opportunity... provided you choose the right plants, timing, and heat management.

At AtmoSerre, we support passionate gardeners, both beginners and experienced, every day. And honestly, summer is perhaps the season that generates the most questions. It's normal: heat can quickly become an enemy if not properly controlled. But when you know how to work with it, the results are simply spectacular. 🍅🥒🌶️

In this guide, we'll detail everything: the vegetables you absolutely must plant, the flowers not to neglect, classic mistakes to avoid, and most importantly, how to adapt your polycarbonate greenhouse so that the heat works for you rather than against you. Let's go! 🚀

The polycarbonate greenhouse in summer: a powerful ally, but one that needs taming ☀️🌡️

Before talking about which plants to grow, we need to address an essential point that many people underestimate: thermal management of the greenhouse in summer. Because yes, in July-August, the inside of a greenhouse can easily exceed 45°C (113°F) if it's poorly ventilated. At that temperature, even the most robust plants suffer.

What makes polycarbonate so interesting is its ability to diffuse light evenly while providing real thermal insulation. Unlike glass, it doesn't create direct burning zones. But that's not enough to solve everything in the middle of summer.

The three pillars of a well-managed summer greenhouse:

• 🌬️ Ventilation: open windows and the door in the morning, ideally before 9 am, to evacuate hot air before it accumulates. Zenithal roof windows are particularly effective because heat naturally rises.
• 💧 Watering: in summer, water needs literally explode. A drip irrigation system is not a luxury, it's almost a necessity to maintain constant humidity without waste.
• 🌿 Partial shading: a shade net placed on the facade or roof can reduce the interior temperature by 5 to 8°C (9 to 14°F). This is significant when it's 38°C (100°F) outside.

Once these three elements are in place, your polycarbonate greenhouse becomes a production machine. The heat accumulated at night protects plants from sudden temperature drops, and during the day, it boosts photosynthesis. It's the virtuous circle of greenhouse gardening. 🌍

🍅 Summer vegetable stars for your greenhouse

Tomatoes: the absolute priority

Let's be honest: if you have a greenhouse, tomatoes are probably the first thing you think of. And for good reason. Growing tomatoes in a polycarbonate greenhouse gives you a considerable head start over outdoor cultivation.

In summer, tomato plants that were sown in February or March reach full maturity. You are in an phase of intensive harvesting from June-July, and if you manage your greenhouse well, you can extend this harvest until October or even November. This is simply impossible in open fields in most regions of France.

Some varieties particularly suited for summer greenhouse cultivation:

• 🍅 Sungold cherry tomato: ultra-productive, sweet, loves heat, and can grow very tall (often over 2 meters / 6.5 ft)
• 🍅 Beefsteak (Cœur de bœuf): large, fleshy, the one that makes generous slices. It requires a little more attention but the result is definitely worth it
• 🍅 Roma: perfect for sauces and canning, disease-resistant, ideal for gardeners who want solid yields without too much hassle
• 🍅 Black Krim: an old variety with a complex, slightly acidic flavor that always surprises guests

Practical tip: In mid-summer, prune your tomatoes regularly, especially the suckers. In a greenhouse, plants tend to grow wildly because they love the conditions. By removing suckers weekly, you concentrate energy on fruit production. The result is visible in a few days. 🛠️

To learn more about growing tomatoes in a greenhouse, feel free to consult our complete guide on growing tomatoes in a polycarbonate greenhouse, where you'll find all the details on sowing, maintenance, and recommended varieties. 🌿

🥒 Cucumbers: pure speed

Cucumbers are one of the most rewarding and largely underestimated vegetables to grow in a summer greenhouse. Their growth is phenomenal once temperatures exceed 22-25°C (72-77°F): we're talking about harvestable fruits in just 50 to 60 days after sowing. In mid-July, you can literally see your plants grow day by day.

In a polycarbonate greenhouse, cucumbers thrive in a perfectly suited environment: constant heat, controllable relative humidity, and protection from external pests. Varieties to favor:

• 🥒 Marketmore: the classic, reliable, productive, easy to grow
• 🥒 Lebanese cucumber: thinner, less bitter, perfect for continuous picking
• 🥒 Tanja F1: a Dutch variety very resistant to disease, ideal for beginners

⚠️ Critical point: cucumbers hate excess stagnant water but love ambient humidity. Water regularly but ensure good drainage. In case of water stress, your cucumbers will become bitter. A simple rule: touch the soil 3-4 cm (1-1.5 inches) deep, if it's dry, water. Otherwise, wait.

🌶️ Peppers and chilies: they love the heat

While tomatoes get all the attention, bell peppers and chili peppers truly deserve to be at the heart of your summer planning. These solanaceous plants require even more heat than tomatoes, and that's where the polycarbonate greenhouse makes all the difference.

Outdoors, bell peppers rarely perform at their best in France (except in the South). In a greenhouse? You can easily get 15 to 25 peppers per plant in a season. That's considerable.

Must-try varieties:

• 🌶️ California Wonder: the perfect red bell pepper, fleshy, sweet, turning from green to red in a few weeks
• 🌶️ Yolo Wonder: slightly later but extremely productive
• 🌶️ Jalapeño: for those who love a kick in their food, this chili variety is perfect for greenhouses as it loves high temperatures
• 🌶️ Sweet elongated pepper: easier to grow than its hotter cousins, very popular in Mediterranean cuisine

Practical tip 💡: bell peppers and chili peppers appreciate soil slightly enriched with potassium. Remember to add well-decomposed compost or a special fruit-vegetable fertilizer when planting. It makes a real difference to the quality of the fruit.

🍈 Melons and watermelons: the summer thrill

Here are two crops that always cause a small revolution in a greenhouse. Growing melons and watermelons in a polycarbonate greenhouse is possible in France, even in regions where the outdoor climate is not at all suitable. And the result... is something you won't forget.

For melons:

The ideal germination temperature is 25 to 30°C (77 to 86°F), which your greenhouse naturally reaches in June-July. Sow directly in pots in May for an August harvest. Charentais varieties (the quintessential French classic) and Ananas melons work very well in a greenhouse.

The often overlooked trick: trellis your melons. By training the plants up stakes or nets, you gain a lot of space and the fruits benefit from better air circulation. The fruits should be supported with small nets or compression stockings (yes, like tights, it's an old gardener's trick that works wonderfully 😄).

For watermelons:

A little more demanding in terms of space, watermelons also thrive in a greenhouse. Today, "mini" varieties are perfect for modest-sized greenhouses:

• 🍉 Sugar Baby: small round, sweet watermelon, perfect for limited spaces
• 🍉 Crimson Sweet: the classic American, very productive and very sweet

🫘 Beans and early broad beans

Often overlooked in summer greenhouse guides, green beans and climbing beans perform exceptionally well in a warm, protected environment. They grow quickly, produce a lot, and don't require much attention.

For summer, prefer pole varieties (climbing) that maximize the vertical space of your greenhouse. Merveille de Venise (yellow wax bean) or Blue Lake (classic green bean) are two reliable choices.

Sowing every 15 days from June to mid-July guarantees continuous production until October. 📈

🥬 Lettuces: play with rapid rotation

Growing lettuce in a greenhouse in summer might seem counterintuitive. And indeed, if you let the temperature get too high, the lettuce will bolt very quickly. But with a few simple tricks, it's entirely manageable.

The trick: choose heat-resistant varieties that are slow to bolt. Batavia lettuce, Romaine, and especially summer cutting lettuce are your best allies. Sow every 2 weeks to always have a continuous supply.

Position your lettuces in areas least exposed to direct sunlight (against north-facing walls or under taller plants like tomatoes). By creating this light natural shade, you slow down bolting and extend the harvest period. 🌿

🌸 Flowers and herbs in the summer greenhouse: don't forget them!

Aromatic herbs: an absolute must

Summer in the greenhouse is also a paradise for aromatic herbs. And frankly, few gardeners realize how spectacular the results can be compared to outdoor cultivation or on a windowsill.

What to grow in terms of herbs?

• 🌿 Basil: this is THE summer plant. It loves heat, hates cold, and in a greenhouse it can reach impressive dimensions. Water at the base, never on the leaves.
• 🌿 Coriander: more delicate because it bolts quickly, but with successive sowings every 15 days, you'll always have some on hand.
• 🌿 Parsley: very versatile, it grows well in summer in a greenhouse provided it doesn't dry out.
• 🌿 Thyme and oregano: these Mediterranean plants love heat and low humidity. Plant them in the warmest areas of your greenhouse, they will thrive.
• 🌿 Dill: perfect to accompany your freshly harvested cucumbers, it grows quickly and loves the heat.
• 🌿 Mint: beware, it's invasive! Grow it in a pot.

Growing your own herbs in a greenhouse is also a way to improve your daily culinary autonomy. And frankly, the difference between basil grown in a greenhouse in mid-summer and supermarket basil is really striking in terms of taste. 🧑🌾

🌼 Flowers in a summer greenhouse: beauty and utility

Flowers are not just aesthetic in a greenhouse. Some attract pollinators who will then visit your vegetables (essential for tomatoes, peppers, and cucumbers), while others naturally repel harmful insects.

Essential flowers for a summer greenhouse:

• 🌼 Marigolds: these are true bodyguards for your vegetables. They repel soil nematodes and whiteflies. Plant them at the edge of your beds.
• 🌼 Nasturtiums: edible, pretty, and they attract aphids to them... away from your tomatoes. A deliberate but very effective sacrifice.
• 🌼 Borage: beautiful blue flower that attracts bumblebees inside the greenhouse. Essential for pollinating your tomato plants if the greenhouse remains closed.
• 🌼 Cosmos: easy, fast, and adds a touch of color and lightness to the growing space.
• 🌼 Flowering Chives: their purple flowers repel aphids, and you can eat both the leaves and the flowers. Double utility guaranteed.

📊 Summary Table: What to Plant in a Greenhouse in Summer by Month

Here is a practical table to help you plan your summer crops in your polycarbonate greenhouse:

🍆 Eggplant: The Great Unsung Hero of Summer Greenhouses

It's not talked about enough, and that's a shame. Eggplant is a fantastic crop for polycarbonate greenhouses. It needs heat, a lot of heat, which the greenhouse naturally provides.

Sown in February-March, eggplants should already be established in your greenhouse by June. They start producing their first fruits from July onwards. And they will continue until October if you manage the greenhouse well.

Preferred varieties:

• 🍆 Violette de Barbentane: a classic French variety, long and purple, very productive
• 🍆 Bonica: a reliable choice, consistent, easy to grow
• 🍆 Listada de Gandia: an old variety with white-purple stripes, beautiful and tasty

A tip we often repeat: don't forget to lightly shake your eggplant plants every two or three days to aid pollination. In a greenhouse without external pollinators, this really makes all the difference to the fruit set rate.

🥑 Zucchini in the Greenhouse: Abundant and Fast

Zucchini is the plant that can overwhelm you if you're not careful. In a polycarbonate greenhouse, it grows at an astonishing speed: from flower to fruit in less than a week in hot weather. If you don't keep an eye on them, you'll end up with arm-sized zucchinis before you've had time to harvest them 😅.

What you need to know:

• Harvest zucchinis when they are small (15 to 20 cm), they are more flavorful and this stimulates production
• Let a few grow larger if you want seeds for the following year
• Zucchini needs a lot of water in summer: up to 3 liters per day per plant during a heatwave
• In a greenhouse, compact varieties (round zucchini or bush varieties) take up less space

Varieties to try: Ronde de Nice (perfect for stuffing), Black Beauty (the classic), Zucchini Striata (striped, very decorative).

🌡️ Managing Summer Heat: The Practical Guide

This is THE topic that makes or breaks summer greenhouse cultivation. Here are our concrete tips, no holds barred.

When to open and when to close?

The golden rule: open early in the morning (from 7-8 am) and close in the late evening (after 7-8 pm). During the day, maximize ventilation. If you have roof vents, they are your best allies because heat rises and escapes naturally.

If you work and cannot be there, invest in automatic thermostatic vent openers. These small devices open when the temperature exceeds a defined threshold (usually 22-25°C) and close when it drops. They cost between €20 and €50 and can save your crops during an unexpected heatwave. 🛠️

Shading: When to use it?

If indoor temperatures regularly exceed 35°C, it's time to consider shading. Options:

• 🌿 Shade net (30 to 50% opacity): the simplest and most economical solution
• 🌿 Shading paint: a special product applied to the walls and rinsed off in autumn
• 🌿 Exterior climbing plants: growing runner beans or Virginia creeper against the south facade of the greenhouse creates gradual natural shading

Watering in Summer: Frequency and Method

In summer, greenhouse plants may require daily watering, or even twice a day during heatwaves. Here are the basic principles:

• 💧 Water preferably in the morning, never in the middle of the heat (between 11 am and 4 pm)
• 💧 At the base of the plants, never on the leaves to avoid scorching and fungal diseases
• 💧 If possible, use room-temperature water: cold tap water can shock plants in hot weather
• 💧 Mulching is your friend: place a layer of compost, straw, or dead leaves at the base of your plants to limit evaporation

🔥 The 5 Most Common Mistakes in Summer Greenhouses

We often see these mistakes. Not to criticize, but so that you don't repeat them.

Mistake #1: Leaving the greenhouse closed on a heatwave day 🚫 This is the most serious. In just one day at 50°C inside, you can lose all your crops. Automate opening if you can't be there.

Mistake #2: Not watering enough (or overwatering all at once) 🚫 Sporadic watering is as bad as no watering. Tomatoes that receive irregular water develop fruit cracking and blossom end rot (a black spot at the bottom of the fruit). Regularity trumps quantity.

Mistake #3: Planting too densely 🚫 We understand the desire to maximize every square centimeter. But plants that are too close together in summer mean air that doesn't circulate, stagnant humidity, and a breeding ground for fungi and diseases. Respect the spacing indicated on seed packets.

Mistake #4: Forgetting pollination 🚫 In a closed greenhouse, insects don't easily enter. And without pollination, no fruit. Regularly open your doors and windows during bumblebee flight hours, and if necessary, manually pollinate your tomatoes with a brush or by gently vibrating them.

Mistake #5: Neglecting pruning and training 🚫 In summer, in a greenhouse, plants grow fast. Very fast. If you don't prune and guide your plants weekly, you'll end up with a jungle where air doesn't circulate, light doesn't penetrate, and diseases take hold.

💡 Advanced Tips to Maximize Your Summer Harvests

Vertical Cultivation: Save Space

In summer, maximizing the vertical space of your greenhouse is a real winning strategy. Tomatoes, cucumbers, climbing beans, trained melons... anything that can go up should go up. This frees up floor space for lower plants (basil, lettuce, radishes), and improves air circulation between plants. 📈

Crop Rotation: Think Ahead

In July-August, start thinking about what you will plant at the end of summer for autumn. AtmoSerre greenhouses allow cultivation almost 365 days a year. When your cucumbers start to fade in August, it's time to sow spinach, lamb's lettuce, or arugula that will take over in September-October.

Compost in the Greenhouse: Your Black Gold 🌍

If you're not yet using compost in your greenhouse, it's a habit you absolutely should adopt. Good, well-decomposed compost improves soil structure, gradually nourishes plants, and improves water retention. In summer, this is particularly valuable.

To learn more about the association between greenhouse and compost, read our dedicated article on greenhouse and compost: it contains really concrete tips that few guides mention.

🏡 Which AtmoSerre greenhouse to choose for summer cultivation?

If you don't already have a greenhouse or are considering upgrading, the question of choosing the right polycarbonate greenhouse is central. Because an undersized or poorly designed greenhouse is a source of constant frustration in summer.

At AtmoSerre, all our greenhouses are designed to withstand extreme climatic conditions, including heatwaves. Our polycarbonate panels (available in 4 mm and 6 mm) diffuse light evenly while limiting heat peaks. The galvanized steel structure ensures optimal rigidity even during strong gusts.

For summer, here is our recommendation:

If you are a beginner and have a standard garden space, L'Intemporelle is our flagship model. Available from 6 m² to 36 m², it offers a generous apex height (perfect for climbing plants like tomatoes and cucumbers), optimized ventilation via its roof vents, and robustness that holds up even in mid-July at 35°C.

It is also the most popular model among our customers for summer cultivation: the photos we receive in July and August show impressive interiors, overflowing with life. 🌱

You can also discover all of our garden greenhouse collection to compare different models according to your space, region, and cultivation ambitions.

And if you want to know more about the brand and our philosophy, visit the AtmoSerre homepage to discover who we are and what drives us every day.

❓ FAQ: What to plant in a greenhouse in summer? Your questions, our answers

🌱 Can you plant in a greenhouse in mid-July?

Yes, absolutely. July is even ideal for sowing green beans, radishes, arugula, and starting autumn lettuce seedlings. The heat promotes ultra-fast germination (sometimes less than 48 hours for beans). The important thing is to water well and manage ventilation to prevent young plants from suffering from the heat.

☀️ How to prevent my greenhouse from overheating in summer?

Open early in the morning, install a shade net on the most exposed sides, water regularly, and if you are away during the day, invest in automatic thermostatic vents. A min/max thermometer placed inside will help you monitor real temperatures and adjust your management.

💧 How often should I water in a greenhouse in summer?

During hot weather, one to two times a day is often necessary for demanding crops like tomatoes and cucumbers. Early morning is the best time. A drip irrigation system with a timer is the ideal solution for automating and standardizing watering without spending hours on it.

🍅 Can you still plant tomatoes in July in a greenhouse?

If you can find potted plants (and it's still possible in garden centers in early July), yes. They will probably produce fruit in September-October. For plants sown in July, the season is too short to expect a real harvest in 2026. However, starting to sow in July to have plants ready in autumn (for winter greenhouse cultivation) is an excellent strategy.

🌿 Is a polycarbonate greenhouse suitable for summer?

Absolutely. Polycarbonate is renowned for its ability to diffuse light without creating hot spots (unlike glass). In summer, its insulating properties also allow for cooler nights, which is beneficial for crops that alternate hot and cold. With good ventilation management, it is the ideal material for summer. To learn more about the subject, you can consult our complete article on why a polycarbonate greenhouse will revolutionize your garden.

🌍 What plants are not recommended for greenhouses in summer?

Avoid vegetables that bolt very quickly due to heat: spinach, classic arugula (except resistant broad-leaf varieties), and radishes (which quickly become woody). These plants are better suited for early spring or autumn cultivation in the greenhouse. In summer, focus on solanaceous, cucurbitaceous, and leguminous plants.

✅ Conclusion: your polycarbonate greenhouse, an ultra-productive summer vegetable garden

As you understand: planting in a greenhouse in summer is not just about what to put in the ground. It's about managing space, heat, water, and timing. But when done well, the results truly live up to the efforts invested.

Tomatoes overflowing, cucumbers growing visibly, melons filling the entire greenhouse with scent at maturity, basil cut fresh every evening to accompany dishes... This is exactly what a well-managed polycarbonate greenhouse allows in the middle of summer.

At AtmoSerre, we are convinced that gardening in a greenhouse means gardening better. With more control, more regularity, and more pleasure. Whatever your region, whatever the size of your garden, there is a greenhouse that suits you. 🌱🔥