Greenhouse Growing for Beginners (UK)

A greenhouse is the single biggest upgrade most UK gardeners ever make. It turns our short, unreliable summers into something you can actually plan around, and it lets you start sowing weeks earlier and keep growing weeks later. This guide walks you through choosing one, setting it up, and what to grow through the year — all written for UK conditions, with no assumption that you've done this before.

The good news: you don't need a heated, glazed palace. An ordinary unheated greenhouse, well managed, will reward you the very first season.

Why grow under cover in the UK

Our climate is the problem a greenhouse solves. UK summers are short, cool and showery, and many of the crops people most want to grow — tomatoes, cucumbers, peppers, chillies, aubergines — come from much warmer places. Outdoors, they sulk in a wet July and barely ripen before the cold returns. Under glass, they get the warmth and shelter they need.

There are four big wins.

Season extension. A greenhouse adds weeks to both ends of the year. You can sow in February when it's still freezing outside, and you can still be picking salad in November. For a beginner, this alone changes what's possible — see our guide to starting a vegetable garden for how the whole year fits together.

Reliable warm crops. Tomatoes that actually ripen, cucumbers that crop for months, chillies that turn red — these are far more dependable under cover. In a poor summer, your greenhouse tomatoes will carry on while outdoor ones struggle. This reliability is the reason most people buy one.

Protection. Wind, hail, heavy rain, slugs and pigeons all do less damage to plants kept under cover. Tender young plants in particular are far safer indoors during our changeable spring.

Propagation space. A greenhouse is a brilliant nursery. You can raise far more seedlings than a windowsill allows, pot them on with room to spare, and have strong plants ready exactly when the weather turns. Even if you grow most things outdoors, the propagation value is huge. It's also a brilliant way to get kids growing, since seedlings come up quickly somewhere warm and bright.

Choosing a greenhouse

You don't have to start with a full greenhouse. There's a sensible ladder of options, and any rung is a real step up from open ground.

The cheapest entry points are a cloche — a small clear cover you pop over a row or an individual plant — and a cold frame, a low, box-like structure with a clear lid. Both warm the soil, shelter seedlings and are perfect for hardening off plants before they go outside. A polytunnel is the cheapest way to get a lot of covered growing space, though it's less tidy and the cover needs replacing every few years. A greenhouse is the most versatile and longest-lasting choice, which is what most beginners settle on.

If you're buying a greenhouse, here are the decisions that matter.

Glass vs polycarbonate

Horticultural glass is the traditional choice. It's clear, lets in the most light, looks smart and lasts for decades. The downsides: it's heavier, more expensive, and panes can crack or shatter — a real consideration if you have children or footballs nearby.

Polycarbonate (usually twin-wall) is lighter, much harder to break, and the air gap gives slightly better insulation. It diffuses light rather than letting it straight through, which actually suits many plants. It can discolour over many years and lightweight panels can pop out in a gale if the frame isn't well anchored. For a first greenhouse in an exposed or family garden, polycarbonate is often the easier, safer pick.

Aluminium vs wood

Aluminium frames are the most common, cheapest and lowest-maintenance — they never need painting and won't rot. They can look a little utilitarian and feel cold, but they're a thoroughly practical choice.

Wooden frames (usually cedar) look beautiful and feel warmer, and they're easy to fix shelving and hooks to. They cost more and need occasional treating to keep them in good order. Choose wood if looks matter and budget allows; otherwise aluminium does the job for less.

Size

This is the decision people most often get wrong — by going too small. A 6ft x 8ft (roughly 1.8m x 2.4m) greenhouse is the popular beginner size, and it's a sensible minimum. The honest truth is that greenhouses fill up far faster than you expect: between seed trays in spring, grow bags of tomatoes in summer and overwintering pots in winter, even a modest one is soon packed.

Siting and base

Put your greenhouse in the sunniest, most sheltered spot you have. Avoid the shade of buildings and trees, and keep it away from the worst of the wind — a frost pocket at the bottom of a slope is the wrong place. Running it roughly north-south lets both sides catch good light through the day.

It needs a firm, level base. A paving-slab or concrete base is solid and easy to keep clean; some people lay slabs round the edge for staging and leave soil borders down the middle for planting tomatoes straight into the ground. Whatever you choose, the greenhouse must be firmly anchored — a strong gust can lift an unsecured one alarmingly. Finally, site it within reach of a water supply; carrying cans a long way every day in summer gets old fast.

Setting up

A bare greenhouse isn't much use until you've kitted it out. None of this is expensive, and you can add bits over time.

Staging. This is the benching that runs along one or both sides, giving you a working surface at a comfortable height for sowing and potting, with seedlings up in the light. Slatted aluminium staging is easy to clean; a removable or collapsible version lets you free up floor space in summer for tall tomato plants.

Ventilation. This is not optional — it's the difference between healthy plants and cooked ones. You need a roof vent and ideally a louvre vent or door low down, so warm air escapes at the top and cooler air is drawn in below. More on this below, because it's one of the two skills that make or break greenhouse growing.

Shading. On a bright summer day a closed greenhouse can hit 40°C and beyond, which scorches leaves and stresses plants. Shade netting, blinds or a coat of shade paint on the glass keeps temperatures sane through midsummer.

A water supply. A water butt fed from the greenhouse guttering gives you rainwater on the spot — kinder to plants than cold tap water and free; it's one of the easiest ways to reuse and recycle around the garden. A nearby tap or a simple length of hose makes daily watering far less of a chore.

A max-min thermometer. This cheap gadget records the highest and lowest temperatures since you last reset it, so you can see overnight cold and midday heat even when you weren't there. It's the single most useful instrument in a greenhouse and takes the guesswork out of when it's safe to move tender plants in or out.

What to grow through the year

A greenhouse earns its keep in every season. Here's how a typical UK year looks.

Spring — propagation and hardening off

This is propagation season. From late February you can sow tomatoes, peppers, chillies and aubergines, then a wider range — courgettes, beans, leeks, brassicas — as spring goes on. Use the planting calendar to time it for your area. The greenhouse gives your seedlings light and warmth a windowsill can't match.

Before any plant raised indoors goes outside, it needs hardening off — gradually getting it used to outdoor conditions over a week or two so it doesn't get a shock. A greenhouse, cold frame or cloche is the ideal halfway house for this. For the broader sowing picture, see our guides to the easiest crops for beginners and improving your soil so plants have somewhere good to go.

Summer — the warm crops

From late spring the greenhouse fills with the crops it does best. Tomatoes are the classic — reliable, productive and far easier under cover; our guide to greenhouse tomatoes covers varieties, planting and feeding, and there's more detail on watering and feeding tomatoes too. Good UK greenhouse varieties include 'Shirley', 'Gardener's Delight' and 'Sungold' for sweetness.

Cucumbers love the warm, humid air under glass — see greenhouse cucumbers for all-female varieties like 'Carmen' and 'Femspot' that crop heavily. Alongside them, peppers, chillies and aubergines all thrive in the same conditions; on warm days, open the door wide so pollinating insects can reach the flowers and set a good crop. If you're tight on space, you can still grow tomatoes outdoors in a sheltered spot — see growing tomatoes and tomatoes in pots.

Autumn and winter — salads and overwintering

When the summer crops finish, the greenhouse doesn't go to sleep. Sown from late summer into autumn, hardy winter salad leaves — winter lettuce, mustards, mizuna, lamb's lettuce, rocket — keep cropping through the cold months. Herbs like parsley carry on too. The unheated structure also shelters tender plants and pots of garlic or overwintering onions getting an early start.

For the full cold-season plan, our guide to getting an unheated greenhouse through the year shows exactly what to sow and when.

The two make-or-break skills: ventilation and watering

If you only master two things, make them these. More greenhouse plants are lost to poor ventilation and poor watering than to anything else, and both are easy to get right once you understand them.

Ventilation and cooling. A greenhouse heats up astonishingly fast on a sunny day, even a cool one. Without airflow, temperatures soar, plants wilt and scorch, and the still, hot air invites pests and disease. The rule is simple: open vents and doors on warm days, close them in the evening. On hot summer days, open everything up first thing and leave it open. Automatic vent openers — which use a wax cylinder to push the roof vent open as it warms — are a brilliant, cheap bit of kit for anyone who's out at work, because they react even when you can't.

Watering. Greenhouse plants depend entirely on you for water, and in summer that can mean watering every single day. Too little and they wilt and drop flowers; too much and roots rot. Water in the morning where you can, aim at the compost rather than the leaves, and check pots and grow bags by lifting or feeling them rather than guessing.

Both skills have a lot more to them — timing, automation, holiday cover, damping down to raise humidity. Our dedicated guide to keeping a greenhouse cool and watered walks through all of it.

Hygiene and pests

Warm, sheltered, still air suits pests as well as plants, so a little routine care keeps problems at bay.

The two to watch for are red spider mite and whitefly. Red spider mite is tiny and thrives in hot, dry air — you'll spot fine webbing and pale, mottled leaves. It hates humidity, so damping down the floor on hot days (which also cools the greenhouse) is a good preventative. Whitefly are little white flies that rise in a cloud when you disturb a plant; sticky yellow traps and a careful eye keep numbers down. Aphids can build up too, and good ventilation reduces all of them by keeping conditions less stuffy.

Once a year — late autumn or early winter is ideal, once the summer crops are done — give the greenhouse a proper clean. Empty it out, wash the glass inside and out to let in maximum winter light, scrub the staging, and sweep up dead leaves and debris where pests and diseases overwinter. This annual reset makes a real difference to the following season's health.

Heated vs unheated

You can grow a great deal in a completely unheated greenhouse, and most beginners should start there — it's cheaper to run and rewards you straight away. An unheated greenhouse gives you all the summer crops, spring propagation and autumn-into-winter salads described above. What it won't do is reliably keep frost off in the depths of winter.

Adding just enough heat to keep it frost-free (around 3–5°C) widens what's possible: you can overwinter tender plants like pelargoniums and fuchsias, protect a wider range of crops, and start sowing even earlier in the new year. A small electric fan heater with a thermostat is the usual way to do this. Be warned that heating a greenhouse through a cold UK winter can use a surprising amount of electricity, so most people heat only a small area, or only when frost actually threatens, rather than keeping the whole structure warm all season.

For a first greenhouse, our honest advice: start unheated, learn the ventilation and watering rhythm, and add a frost-free heater later if you find you want it. You'll get a full, productive year out of it either way.

Where to go next

A greenhouse is a long-term investment that pays you back season after season. Get the basics right — a sunny, sheltered, well-anchored spot; decent ventilation and shading; a daily watering habit; and an annual clean — and you'll be growing more, and more reliably, than you ever could outdoors alone.

From here, dig into the crop guides for greenhouse tomatoes and greenhouse cucumbers, master the climate with keeping a greenhouse cool and watered, and plan the cold months with an unheated greenhouse through the year. For everything beyond the glass, the getting started hub covers soil, sowing and planning your whole growing year.