🌿🏡 When to Plant Vegetables in a Greenhouse (UK Guide)

🌿🏡 Introduction: Make the Most of Protected Growing

A greenhouse gives UK gardeners a huge advantage. It provides warmer temperatures, shelter from wind and rain, and protection from frost, allowing you to start vegetables earlier, grow tender crops reliably, and extend harvests well beyond the outdoor season.

This guide explains when to plant vegetables in a greenhouse, broken down by month and crop type, so you know exactly what to sow and when for the best results.

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🌡️ Why Greenhouse Planting Works So Well

A greenhouse allows you to:

✔ Start sowing weeks earlier
✔ Grow frost-tender vegetables safely
✔ Control temperature and moisture
✔ Reduce weather damage
✔ Extend harvesting into autumn and winter

However, timing still matters — even under glass.

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📅 Greenhouse Vegetable Planting Calendar (UK)

❄️ January – Early Starts (Heated or Very Bright Greenhouses)

Best for slow, long-season crops.

✔ Chillies
✔ Sweet peppers
✔ Aubergines
✔ Onions (from seed)
✔ Leeks

Conditions needed:

• Heat (18–22°C)
• Strong light (grow lights ideal)

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🌱 February – Early Greenhouse Sowing

✔ Tomatoes (early varieties)
✔ More chillies and peppers
✔ Lettuce
✔ Spinach
✔ Early brassicas

Unheated greenhouses may still need fleece at night.

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🌸 March – Main Greenhouse Sowing Begins

✔ Tomatoes
✔ Cucumbers (greenhouse types)
✔ Courgettes
✔ Squash
✔ Sweetcorn
✔ Basil
✔ Salad leaves

Ventilate on sunny days to prevent overheating.

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🌼 April – Transition Month

✔ Cucumbers
✔ Courgettes
✔ Squash
✔ Beans (early starts)
✔ Herbs

Start hardening off plants that will go outdoors in May.

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☀️ May – Summer Crops Take Over

✔ Plant tomatoes, peppers, cucumbers into final greenhouse positions
✔ Succession sow salads and herbs
✔ Start autumn brassicas

Greenhouse temperatures rise quickly — ventilation is essential.

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🌻 June – August – Peak Greenhouse Growing

✔ Tomatoes, cucumbers, peppers cropping heavily
✔ Basil, coriander, parsley
✔ Continuous salad sowings

Avoid sowing slow crops — focus on harvesting and maintenance.

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🍂 September – Autumn Greenhouse Sowing

✔ Spinach
✔ Winter lettuce
✔ Pak choi
✔ Mizuna
✔ Spring onions

Greenhouses extend autumn harvesting significantly.

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❄️ October – November – Overwintering Crops

✔ Spinach
✔ Winter salads
✔ Garlic (containers or beds)
✔ Spring onions

Growth slows, but crops stay harvestable.

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🥬 What Grows Best in a Greenhouse?

🌶️ Warm-Loving Vegetables (Big Winners)

✔ Tomatoes
✔ Chillies
✔ Peppers
✔ Aubergines
✔ Cucumbers

🥬 Early & Late Crops

✔ Lettuce
✔ Spinach
✔ Rocket
✔ Pak choi
✔ Spring onions

Greenhouses shine at season extension, not just summer growing.

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🌱 When to Move Greenhouse Plants Outdoors

Approximate UK planting-out times:

• Southern UK: late April–early May
• Midlands & North: mid–late May
• Scotland / exposed areas: late May–June

Always harden off first and watch night temperatures.

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🌬️ Ventilation & Temperature Tips

✔ Open doors and vents daily in spring/summer
✔ Close early evening to retain warmth
✔ Use shade netting in heatwaves
✔ Avoid watering late in the day

Poor airflow causes disease faster than cold.

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🚫 Common Greenhouse Planting Mistakes

❌ Sowing too early without enough light
❌ Overcrowding plants
❌ Forgetting ventilation
❌ Overwatering in cool weather
❌ Treating greenhouse like outdoors

Greenhouses amplify mistakes as well as success.

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❓ FAQs

Can I plant vegetables in an unheated greenhouse in winter?

Yes — hardy salads and spinach survive, but growth is slow.

Is a greenhouse better than a polytunnel?

Greenhouses offer better light and structure; polytunnels offer more space. Both are excellent.

Do greenhouse vegetables need more feeding?

Yes — faster growth means nutrients are used quickly.

Can I grow vegetables year-round in a greenhouse?

With planning, you can harvest something in every month.

What’s the easiest greenhouse vegetable for beginners?

Tomatoes, lettuce, and cucumbers are the most forgiving.

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