How to Extend the Vegetable Season with a Greenhouse
The complete guide to harvesting all year round, even in the middle of winter!
Why use a greenhouse to extend your vegetable season?
With a greenhouse, you can grow vegetables 12 months a year, even in cold regions or during winter. Whether you are an amateur gardener or a market gardener, a greenhouse creates an ideal microclimate to:
- Start your seedlings earlier (as early as February).
- Protect your plants from frost, wind, and diseases.
- Harvest fresh vegetables in autumn and winter (salads, spinach, radishes…).
- Grow sensitive varieties (tomatoes, peppers, eggplants) out of season.
- Optimize your space and increase your production (up to 3 times more than outdoors).
Did you know? An unheated garden greenhouse can gain 5 to 10°C compared to the outside, enough to grow hardy vegetables even in January!
Which vegetables to plant in a greenhouse in winter?
Cold-resistant vegetables (harvest from autumn to spring)
These varieties can withstand low temperatures (up to -5°C with protection):
| Vegetable | Sowing/Planting Period | Ideal Temperature | Harvest | Tips |
|---|---|---|---|---|
| Spinach | September to November | 5°C – 15°C | October to April | Direct sowing in rich soil. Mulch to limit frost. |
| Salads (lettuce, arugula, lamb's lettuce) | August to October | 10°C – 18°C | November to March | Choose winter varieties (e.g., 'Reine de Mai' lettuce). |
| Radishes | All months (except frost) | 10°C – 20°C | 6-8 weeks after sowing | Quick harvest (ideal for gaps between two crops). |
| Cabbage (cauliflower, kale, kohlrabi) | July to September | 5°C – 18°C | October to May | Protect with a winter fleece in case of severe cold. |
| Leeks | Spring (transplanting in autumn) | 5°C – 20°C | December to April | Mound soil around stems to blanch them. |
| Carrots | July to August | 7°C – 24°C | October to March | Light, deep soil. Store in place under mulch. |
| Onions and garlic | October to November | 5°C – 20°C | May to July | Plant in waning moon for better preservation. |
| Parsnips and beets | April to June (winter harvest) | 5°C – 18°C | November to March | Harvest after the first frosts for more flavor. |
Vegetables to grow in a heated greenhouse (or mild region)
For fruit vegetables and heat-loving plants:
| Vegetable | Sowing/Planting Period | Ideal Temperature | Harvest | Tips |
|---|---|---|---|---|
| Tomatoes | February-March (under cover) | 18°C – 25°C | July to October (or all year in a heated greenhouse) | Stake and prune. Avoid excess humidity. |
| Peppers / Eggplants | January-February | 20°C – 28°C | July to November | Sow in pots indoors before transplanting. |
| Cucumbers | March-April | 20°C – 28°C | July to September | Grow upwards: install a string or trellis. |
| Melons | April-May | 20°C – 30°C | August to October | Heated greenhouse essential. Black mulch to warm the soil. |
| Zucchini | April-May | 18°C – 25°C | July to September | 1 plant/m² to prevent disease (powdery mildew). |
Aromatics and secondary plants
- Parsley, chives, chervil: Sow in September for winter harvest.
- Basil: Grow in a pot near a heat source.
- Edible flowers (nasturtiums, borage): Sow in March to attract pollinators.
Our advice:
- Combine crops (e.g., tomatoes + basil).
- Use grow tables to save space.
- Sow in waxing moon for leaves (salads), in waning moon for roots (carrots).
How to use a greenhouse in winter? Techniques for a controlled environment
Preparing your greenhouse for winter
- Clean: Disinfect with soapy water or white vinegar to prevent diseases.
-
Insulate:
- Double glazing or plastic sheeting (for tunnel greenhouses).
- Bubble wrap on the walls at night.
- Mulch the soil (straw, wood chips) to retain heat.
-
Protect:
- Winter fleece (to be put on in the evening and removed during the day).
- Thermal cover for the coldest nights.
- Supplemental heating (if temperature < 0°C).
Managing temperature and humidity
-
Ideal Temperature:
- Winter vegetables: 5°C – 15°C.
- Mediterranean vegetables: 18°C – 25°C.
-
Humidity:
- 40-60% for most plants.
- Ventilate for 10-15 min/day to limit condensation (risk of downy mildew).
-
Light:
- Clean windows to maximize light (especially in December-January).
- Horticultural LED lighting if sunlight is scarce.
Organizing plantings for continuous harvesting
Monthly Calendar:
- January-February: Sow radishes, spinach under cold frames. Protect salads.
- March: Transplant tomatoes, peppers.
- April: Plant zucchini. Mound soil around leeks.
Rotation Example:
| Month | Action |
|---|---|
| January | Sow radishes, spinach under cold frames. Protect salads. |
| February | Sow tomatoes, eggplants indoors. |
| March | Transplant peppers. Sow carrots directly in the ground. |
| April | Plant zucchini. |
Best practices for successful greenhouse cultivation
Optimizing space
- Vertical crops: Cucumbers, climbing beans.
- Companion planting:
- Tomatoes + marigolds (against aphids).
- Carrots + leeks (against carrot rust fly).
- Rotation: Do not plant the same family in the same place 2 years in a row.
Irrigation and nutrients
- Watering:
- Drip irrigation for precise watering.
- Avoid wetting the leaves (risk of diseases).
- Fertilizer:
- Compost or well-rotted manure before planting.
- Manures (nettle, comfrey) monthly.
Regular maintenance
- Weed once a week.
- Monitor for pests (slugs, aphids).
- Prune plants (tomatoes, eggplants) to promote production.
Cold greenhouse vs. heated greenhouse: Which solution to choose?
| Greenhouse Type | Advantages | Disadvantages | Suitable Vegetables |
|---|---|---|---|
| Unheated greenhouse | Economical, ecological | Limitation: hardy vegetables only | Spinach, salads, radishes, leeks |
| Heated greenhouse | Year-round cultivation | Energy cost | Tomatoes, peppers, melons, eggplants |
| Mini greenhouse | Ideal for balconies | Limited space | Aromatics, radishes, lettuces |
| Lean-to greenhouse | Better insulation | Less light | Mediterranean plants |
| Tunnel greenhouse | Affordable, modular | Less aesthetic | Root vegetables, gourds |
Budget:
- Unheated greenhouse: €500 – €2,000.
- Heated greenhouse: €2,000 – €10,000 (depending on size and system).
The advantages of a greenhouse for your vegetable garden
- Extend the season: Harvest 2 to 3 months longer than outdoors.
- Protect your plants from bad weather (hail, wind, frost).
- Control the environment (temperature, humidity, light).
- Grow rare varieties (melons, eggplants in cold regions).
- Reduce diseases thanks to a closed space.
- Organic and local production all year round.
Ready to start? Our tips for getting started
-
Choose a suitable greenhouse:
- Glass greenhouse: Aesthetic and durable (ideal for gardens).
- Tunnel greenhouse: Economical and easy to assemble.
- Mini greenhouse: Perfect for balconies.
- You can favor greenhouses made in France like Serre La Française.
-
Install it in the right place:
- South-facing for maximum sunlight.
- Sheltered from the wind (near a wall or hedge).
-
Equip yourself:
- Thermometer/hygrometer (to monitor the climate).
- Winter fleeces and covers.
- Irrigation system (drip irrigation).
-
Follow a calendar:
- Early sowing in February-March.
- Winter harvests (spinach, salads).
FAQ: Your questions about winter greenhouse cultivation
Can you grow without heating in winter?
Yes! With a well-insulated greenhouse and hardy vegetables (spinach, leeks). Mulching and a winter fleece are often enough.
How to prevent frost in a greenhouse?
Double glazing, thermal cover, black water bottles (store heat during the day).
What is the minimum temperature for an unheated greenhouse?
0°C (with protection). Below that, use supplemental heating.
When to sow tomatoes in a greenhouse?
Late February (in mild regions) or March (elsewhere), with indoor sowing before transplanting.
How to water in winter?
Little and regularly (the soil should remain cool, not waterlogged). Avoid icy water.
Comments (0)
There are no comments for this article. Be the first one to leave a message!