What to Grow in a Polytunnel: UK Year-Round Crop Calendar

Quick answer: What to grow in a polytunnel in the UK includes tender summer crops (tomatoes, chillies, cucumbers, and aubergines) followed by frost-hardy winter salads (mizuna, winter purslane, spinach, and overwintered broad beans). A polytunnel extends the British growing season to a full 12 months without artificial heating.

Erecting a polytunnel is one of the most transformative upgrades you can make to a UK garden or allotment plot. By modifying the surrounding microclimate, a polytunnel protects plants from cold easterly winds, buffers against late spring frosts, and captures precious solar warmth throughout dull, overcast British summers.

However, many gardeners underutilise their tunnels by treating them merely as temporary summer tomato shelters that sit abandoned and weed-choked from October to April. Knowing what to grow in a polytunnel throughout all four seasons allows you to harvest crisp, fresh produce every single week of the year without spending a penny on artificial heating.

By planning smooth seasonal successions, choosing space-saving cultivars, and maintaining healthy ventilation, you can turn a basic polyethylene hoop structure into a highly productive year-round food sanctuary.

The 12-Month UK Polytunnel Growing Calendar

To achieve continuous cropping, structure your polytunnel into two main seasonal shifts: the Summer Phase (May to October) and the Winter/Spring Phase (October to May).

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To coordinate seasonal bed transitions with the rest of your allotment, review our companion guide on crop rotation allotment.

Summer Heat-Lovers: Tomatoes, Chillies and Cucumbers

From late spring through early autumn, the polytunnel becomes a high-heat engine for crops that struggle outdoors in Britain:

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1. Cordon Tomatoes

Cordon (indeterminate) tomatoes are the cornerstone of the summer tunnel. Train vines vertically up heavy jute twine tied to overhead crop bars. Prune out all lateral sideshoots weekly to focus plant energy on 6 to 8 heavy flower trusses.

For diagnostic troubleshooting on curling leaves or virus vectors in greenhouse nightshades, review our guide to tomato leaf curl diagnostics.

2. Cucumbers and Aubergines

Choose all-female F1 hybrid cucumbers like Passandra. They produce sweet, seedless fruits without requiring pollination. Aubergines demand the hottest, sunniest position near the centre of the tunnel.

Winter Polytunnel Growing: The Secret Second Season

When outdoor gardens freeze solid under snow and ice, a cold polytunnel maintains an active winter salad garden:

• Winter Purslane (Claytonia / Miner's Lettuce): One of the most reliable winter salads under cover. Survives hard freezes beneath plastic and produces juicy, succulent spade-shaped leaves packed with vitamin C from November to April.
• Oriental Brassicas (Mizuna, Mibuna, Pak Choi, Tatsoi): Fast-growing peppery greens that thrive in cool conditions. Harvest outer leaves continuously for stir-fries and fresh salads.
• Corn Salad (Lamb's Lettuce / Mache): Tender, nutty green rosettes that withstand sub-zero conditions without leaf damage.
• Land Cress and Rocket: Delivers robust peppery flavour all winter long.

During severe sub-zero cold snaps, drape a layer of horticultural fleece directly over your winter salad beds at night to provide an extra 2°C to 4°C of frost protection.

Space-Efficient Polytunnel Layout Ideas

How you configure your internal beds determines how much food you can harvest and how easily you can navigate with tools.

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1. Bed Width: Keep side beds between 1.0 m and 1.2 m wide so you can comfortably reach the back without stepping on the soil.
2. Central Path: Maintain a 60 cm to 75 cm central pathway laid with gravel, woodchips, or flagstones. This width allows easy access for wheelbarrows and harvest crates.
3. Overhead Crop Bars: Install steel crop support bars across the top hoops. These provide structural rigidity against winter winds and serve as anchor points for vertical plant support twines.

For precision spacing and thinning techniques for direct-sown tunnel crops, consult seedling care thinning spacing direct sowing.

Climate Management: Ventilation, Humidity and Shading

A polytunnel is an enclosed ecosystem that requires proactive management:

• Ventilation Is Paramount: High humidity plus stagnant air is the main driver of grey mould (Botrytis cinerea). Powdery mildew works differently — its spores need no leaf wetness and it is worst on plants under drought stress, so keep roots evenly moist as well as keeping the air moving. Open both end doors on all mild days to encourage gentle air exchange.
• Summer Shading: When temperatures exceed 30°C in July, drape 50% shade netting over the roof, or fit shade cloth inside. Shading washes are made for glass and are best avoided on polythene, where they are hard to remove.
• Watering Rhythms: In summer, water deeply at the base of plants in the early morning. In winter, water sparingly once every ten to fourteen days, ensuring foliage remains completely dry overnight to avoid fungal decay.