Key takeaways
- A polytunnel gives far more covered growing space for the money than a greenhouse
- It adds a few weeks at both ends of the season and keeps hardy salads going all winter
- Tomatoes, peppers, aubergines and melons crop far more reliably under cover
- Open the doors on every warm day from late spring, or plants cook
- Expect to replace the polythene cover roughly every five years
- Buy one size bigger than you think, as long as it suits the garden
For most people who grow their own veg, a polytunnel is worth it. It gives a lot of covered growing space for the money, stretches the season at both ends and turns tricky crops like peppers and melons into reliable ones. It isn’t for everyone, though. It is big, it is plastic, and it needs someone to open the doors on warm days.
This guide helps you decide whether a tunnel suits you and your garden. If you have already decided to grow under cover and are choosing between structures, the side-by-side guide to polytunnel vs greenhouse covers cost, space and lifespan in more detail.
What does a polytunnel actually do for you?
A polytunnel is a steel hoop frame covered in a tough polythene sheet. It traps warmth, keeps off wind and rain, and gives you open beds at ground level. That adds up to four real benefits.
- More space for the money. A tunnel covers far more ground than a greenhouse at a similar price. You get room for whole rows of tomatoes, beans and salad.
- A longer season. Sowing starts a few weeks earlier in spring, and summer crops keep going later into autumn.
- Tender crops that ripen. Peppers, chillies, aubergines and melons that sulk outdoors in a cool summer crop far more reliably under cover.
- Weather protection. Hail, heavy rain, gales and late frosts are kept off crops that would otherwise be flattened or scorched.
This is what all that space buys you: a full row of tomatoes on one side, with peppers and salad crops sharing the other bed.
Which crops make a polytunnel worth having?
The crops that gain most are the warmth lovers that struggle outdoors in a grey British summer.
| Crop | Outdoors in most of the UK | In a polytunnel |
|---|---|---|
| Tomatoes | Hit and miss, blight risk in wet summers | Reliable, longer picking season |
| Peppers and chillies | Often too cool to ripen | Ripen well by late summer |
| Aubergines | Rarely worth it | Good crops in a warm summer |
| Melons | Very hard work | Possible with good care |
| Cucumbers | Ridge types only | Greenhouse types crop heavily |
| Winter salad | Battered by weather | Pick through autumn and winter |
Tomatoes are the big win for many people. Tomato blight spreads on wet leaves, so keeping the rain off gives your plants a much better chance in a damp August. The guide to tomato diseases in polytunnels covers the problems that do turn up under cover, such as leaf mould and grey mould.
Rain runs straight off the cover, so the tomato leaves underneath stay dry. That alone cuts the risk of blight in a wet summer.
Can you use a polytunnel all year round?
Yes, and that is a large part of what makes it worth it. Summer is for tomatoes, cucumbers and peppers. Autumn and winter are for hardy leaves.
Sow winter salads such as lamb’s lettuce, winter purslane, mizuna, rocket and land cress from late summer into early autumn. They grow slowly through winter and give you pickings on mild days. Spinach, chard and spring onions do well too. In early spring the tunnel becomes your nursery for hardening off seedlings before they go outside.
A tunnel is not frost-proof. It takes the edge off frost and keeps off wind and wet, but it can still freeze inside on a hard night. Keep tender plants somewhere heated over winter. The polytunnel calendar sets out what to sow and plant in each month.
Hardy salad leaves carry on quietly in winter under cover. Pick a few leaves from each plant on mild days and they keep coming.
The honest downsides of a polytunnel
A tunnel has real drawbacks, and it is better to know them before you buy.
Open the doors early on sunny days from late spring. A shut tunnel heats up fast, and tomatoes and peppers drop their flowers when it does.
- The look. A big white plastic hoop dominates a small garden. Green tinted covers soften it, but it is still a tunnel.
- Venting every warm day. On a sunny day a closed tunnel gets very hot, very fast. From late spring someone needs to open the doors in the morning and shut them in the evening. Side vents or a door that opens at both ends help a lot.
- Watering. No rain reaches the beds, so everything is watered by you. A seep hose on a timer takes the strain.
- Replacing the cover. Polythene breaks down in sunlight. Plan on a new cover roughly every five years. It is a job for two people on a calm, mild day.
- Wind. A badly anchored tunnel can lift or tear in a gale. Anchor it properly and keep the doors shut in storms.
Tunnels are humid, so pests such as red spider mite and aphids, and diseases like grey mould, can build up. Good airflow and tidy beds keep them in check. The polytunnel maintenance guide covers cleaning, cover care and repairs.
Who is a polytunnel not worth it for?
A tunnel is probably not for you if any of these sound familiar.
- You rarely grow veg. A few pots of herbs and a couple of tomato plants don’t need a tunnel. A cold frame or growhouse will do.
- Nobody is around in the day. Unless you add automatic vents or leave doors open, a closed tunnel can scorch plants on a sunny day.
- The only spot is shady or very exposed. A tunnel needs good light and a site that isn’t a wind tunnel already.
- You want something that looks smart. A glasshouse is easier on the eye and suits a garden used for sitting out.
What size polytunnel should you buy?
Buy the biggest tunnel that sits comfortably in your space. Almost everyone who buys one wishes it was bigger within a couple of seasons.
Even a small tunnel fits at the end of a terraced garden. Leave a path all round so you can reach the cover and anchors.
As a rough guide, a 2m x 3m tunnel suits a small garden and gives a couple of beds for summer crops. A 3m x 6m tunnel is a good size for a family growing a lot of its own food. Leave room around the outside to walk, fix the cover and dig in the skirt. Also make sure you can stand up in the middle and walk the path comfortably.
Garden tunnels are often treated like sheds and outbuildings under planning rules, but limits on height, position and coverage apply. The guide to polytunnel planning permission explains what to check first.
Is a polytunnel better than a greenhouse?
For space per pound, yes. For looks, heat and potting comforts, a greenhouse wins.
A greenhouse is better for staging, seed trays and a few prize plants in pots. A tunnel is better for bulk crops grown in the ground. Plenty of growers end up with both, using the greenhouse as a nursery and the tunnel as the productive kitchen garden.
A tunnel and a small greenhouse work well together. The tunnel does the bulk crops, and the greenhouse handles seedlings and potting.
Common mistakes that make a polytunnel a regret
- Keeping the doors shut on warm days. Overheating makes tomatoes and peppers drop flowers. Open up early, before it gets hot.
- Skipping proper anchoring. Follow the maker’s instructions for the base and anchors so the first gale doesn’t lift it.
- Crowding the plants. Packed plants and still, humid air invite mould and pests. Give each plant the spacing on the seed packet.
- Leaving it empty in winter. An empty winter tunnel wastes half its value. Sow winter salads in late summer.
- Buying too small. Space fills fast. If in doubt, go one size up.
Frequently asked questions
Is a polytunnel worth it for a small UK garden?
Often yes, if you grow veg and have a sunny spot. A small 2m x 3m tunnel still holds a summer of tomatoes, peppers and cucumbers, then winter salads. If the garden is mainly for sitting out, a small greenhouse or a cold frame may suit it better.
How long does a polytunnel last?
The frame lasts many years; the cover needs replacing roughly every five years. A good UV-stabilised polythene often lasts longer, especially if it is fitted tight and kept clean. Replacing it is a job for two people on a calm, mild day.
Are polytunnels worth it compared to a greenhouse?
For sheer growing space, yes, a polytunnel gives more for the money. A greenhouse looks smarter, holds heat a little better and suits staging and potting. Many keen growers end up with both.
What can I grow in a polytunnel that I cannot grow outdoors?
Peppers, aubergines, melons and sweet potatoes do far better under cover. Outdoors in most of the UK they struggle to ripen in a cool summer. Tomatoes and cucumbers also crop more reliably, and tomatoes are better protected from blight.
Do polytunnels work in winter?
Yes, for hardy crops such as winter salads, spinach and spring onions. The tunnel keeps off wind and rain and takes the edge off frost. It can still freeze inside on hard nights, so it is not a home for tender plants unless you add heat.
Are polytunnels worth it if I already have a greenhouse?
Often yes, because the two do different jobs. Keep the greenhouse for seedlings, staging and a few pots. Use the tunnel’s open beds for bulk tomatoes, climbing beans, cucumbers and winter salads.
What is the biggest disadvantage of a polytunnel?
Ventilation is the biggest day-to-day chore. On a sunny day a closed tunnel overheats fast, so someone needs to open the doors. Close behind that are the look and replacing the cover every few years.
Decided a tunnel is for you? The guide to getting more from every square metre of a polytunnel shows how to plan the beds so it pays its way, and there are more guides on the how-to hub.
Our team produces practical UK gardening guidance from source research, contributor records and established horticultural practice. Editorial standards are overseen by Matt W.
