Greenhouse Growing Guide: UK Month-by-Month Calendar

Written by Matt W | Co-Founder, Greenhouse Stores
Updated 24 August 2026

A UK greenhouse lets you start crops earlier, protect tender plants and keep harvesting later. This month-by-month calendar covers sowing, planting, watering, ventilation and winter protection for UK conditions. Most summer crops grow best between 18°C and 24°C. Ventilate before temperatures exceed 27°C, and shift sowing dates one to two weeks later in northern England and Scotland.

Key takeaways

Setting up your greenhouse for growing

Before sowing, check the position, base, ventilation and working space. These decisions affect daily use more than decorative extras.

Choosing the right location

Choose the brightest practical position. A south-facing site usually receives the most light. East-facing sites warm earlier in the day. Avoid deep shade, especially during spring when seedlings need steady light. Our tomato guide explains the light and temperature needs of summer crops.

Keep the roof clear of overhanging branches. Falling wood can damage glazing, while leaves block gutters and reduce winter light. Leave enough room to clean the outside safely.

Use a hedge or open fence as a windbreak where the site is exposed. Keep it far enough away to avoid shade and turbulent air. Our greenhouse positioning guide covers the trade-offs.

Foundation and base preparation

A greenhouse needs a level base that matches its frame and anchoring method. An uneven base can twist the frame. Doors may bind and glazing may sit under stress.

Concrete, paving and perimeter foundations can all work. Follow the chosen greenhouse manufacturer's dimensions and anchoring instructions. Our base preparation guide explains each option.

Choosing the right glazing for growing

Your choice of glazing directly affects how well your greenhouse holds heat and protects your plants. Here's how the three main options compare for growing:

For most growers, toughened glass gives the best balance of light, safety, and durability. Polycarbonate is lighter than glass and retains more heat. Secure every panel according to the manufacturer's wind-loading instructions. Our buying guide covers glazing options in more detail.

Interior layout: staging, benches, and floor space

Greenhouse staging puts seed trays at working height. The space underneath can hold pots and equipment. Keep floor space available for tall summer crops.

I'd suggest staging along one side and leaving the other side for border planting or grow bags. In a greenhouse at least 8ft wide, staging can run down both sides. Keep the central path at least 60cm wide.

Temperature and ventilation control

Getting temperature right is the single biggest factor in greenhouse growing success. Most greenhouse crops grow best between 18-24°C during the day and 10-15°C at night. Go above 27°C and you'll see blossom drop on tomatoes, bolting in lettuce, and wilting in cucumbers. Go below 5°C and tender seedlings will die.

Understanding greenhouse temperatures by season

Use a maximum-minimum thermometer and record the readings daily. After several weeks, you will understand how quickly your greenhouse heats and cools.

Ventilation: the most important factor

Ventilation controls heat, humidity and air movement. For larger glasshouses, one square metre of ridge ventilation per five square metres of floor area is a useful starting point. Small greenhouses may need proportionally more.

Open roof vents, side vents and the door on warm, bright days. Aim to keep the greenhouse below 27°C. Automatic openers help, but they take time to respond.

Automatic vent openers use a wax cylinder and need no electricity. They are useful when nobody is home. Keep the door and side vents available because roof vents alone may not prevent overheating. See our greenhouse accessories.

Heating your greenhouse in winter

During sunny weather, an unheated greenhouse can become much warmer than the garden. Overnight temperatures may track outside conditions closely. On clear nights, the greenhouse can briefly become colder than the surrounding air. Use a maximum-minimum thermometer and protect tender plants when frost is forecast.

Bubble insulation reduces draughts and slows heat loss. Keep vents usable and remove insulation when spring light levels increase. Compare heating options using the running cost and thermostat settings, not the heater's wattage alone.

Shading and cooling in summer

Use the minimum shading needed to keep plants below damaging temperatures. External blinds and external netting cool more effectively than internal materials. Damping hard paths raises humidity and can help during bright weather.

Watering and humidity management

Water at soil level during the morning. Leaves and paths then have time to dry before evening. This reduces the damp conditions that favour grey mould.

Check pots and grow bags daily during warm weather. Plant size, container volume and weather all change demand. Keep compost evenly moist rather than soaking dry pots.

Collect rainwater from greenhouse gutters where possible. Keep water butts covered and clean. Water stored inside or beside the greenhouse is less likely to be very cold.

Greenhouse growing month by month in the UK

This calendar uses typical Midlands conditions. Move sowing one or two weeks later in Scotland and northern England. Southern and sheltered gardens may start earlier. Weather matters more than the date.

How to read the calendar: actions marked as heated need a propagator or frost-free greenhouse. Other actions suit an unheated greenhouse when local conditions allow.

Best crops to grow in a UK greenhouse

These crops use greenhouse warmth and shelter well. Choose varieties suited to protected growing, then match them to your available space.

Tomatoes

Tomatoes make good use of greenhouse warmth and shelter. Final yield depends on the variety, root space, light, feeding and watering. Cordon plants also need reliable support and weekly side-shoot checks.

Sow tomatoes with heat from February. Pot them on as roots fill each container. Move plants into final positions when nights remain above 10°C. Feed after the first fruit truss sets.

For detailed growing instructions, see our greenhouse tomato growing guide.

Greenhouse cucumbers produce smoother, longer fruit than outdoor varieties and crop heavily from June through September. Choose all-female varieties (like 'Passandra' or 'Bella') to avoid bitter fruit, these don't need pollinating.

Cucumbers prefer more humidity than tomatoes. Place them at the far end if both share one greenhouse. Train the main stem upwards and follow the seed supplier's pruning advice.

See our cucumber growing guide for full instructions.

Peppers and chillies

Sweet peppers and chillies need a long, warm season. Sow with heat from February and pot on before roots become crowded. Harvest timing depends on variety and spring light.

Some chilli varieties benefit from pinching, while others branch naturally. Keep compost evenly moist during flowering and fruiting. Our pepper growing guide covers variety-specific care.

Aubergines

Aubergines need a long, warm season. Sow with heat during January or February. Check leaf undersides for red spider mite and maintain steady watering. Avoid crowding plants because still air encourages disease.

Lettuce and salad leaves

Lettuce is the quickest-reward crop for greenhouse growers. Sow direct into trays and you can cut your first leaves in as little as 3-4 weeks. "Cut and come again" varieties give you multiple harvests from one sowing. Lettuce can crop for much of the year under glass. Choose heat-tolerant varieties and add shade during the hottest weeks.

Sow a small batch every two or three weeks for a steady supply. Move trays into partial shade during the hottest weather.

Herbs

Basil, coriander, parsley and chives grow well in pots under cover. Keep mint in its own container because its roots spread quickly. Our herb garden guide covers container choices and seasonal care.

Strawberries

Greenhouse strawberries can crop earlier than outdoor plants. Grow them in pots or baskets to keep fruit away from damp soil. Open vents during flowering so pollinating insects can enter. See our strawberry growing guide.

Exotic and unusual crops

A greenhouse opens up crops that don't normally grow outdoors in the UK. Melons (try 'Charentais' or 'Sweetheart'), physalis (ground cherries), ginger, and even orchids all thrive in a warm greenhouse. Want to try something different? Read our guide to 25 unusual things to grow in a greenhouse.

More crops you can start in a greenhouse

A greenhouse is also useful for starting vegetables, leafy greens and cucurbits. Transplant them outdoors or keep suitable crops under cover:

Asian Greens

Broccoli

Brussels Sprouts

Cabbage

Kale

Chard

Spinach

Endive

Gourds & Pumpkins

Melons

Squash

Potatoes

Physalis

Pepino

Greenhouse pest and disease management

A warm, sheltered greenhouse is well suited to your plants, and for pests. The enclosed environment means populations can build up fast, so early detection is everything.

Common greenhouse pests

Red spider mite: Tiny (0.5mm) mites that live on the undersides of leaves, causing yellowing and fine webbing. They thrive in hot, dry conditions. Raise humidity by misting and damping down. Biological control (Phytoseiulus persimilis) works well if introduced early in the season (May–June).

Whitefly: Small white flying insects that cluster on the undersides of leaves, particularly on tomatoes. Hang yellow sticky traps above plants from April to give early warning. Encarsia formosa (a tiny parasitic wasp) is the most effective biological control. Introduce it when daytime temperatures are consistently above 18°C.

Aphids (greenfly/blackfly): Sap-sucking insects that weaken plants and spread viruses. Squash small colonies by hand or blast with a spray of water. Introduce ladybird larvae for biological control.

Disease prevention

Still air, wet foliage and old plant debris increase disease pressure. Use these three habits:

1. Ventilate, ventilate, ventilate. Still, humid air breeds grey mould (botrytis) and mildew.
2. Water at soil level, not from above. Wet leaves in cool evenings are the main cause of fungal outbreaks.
3. Clean up. Remove dead leaves, spent plants, and fallen fruit immediately. These harbour disease spores.

Remove spent plants in autumn. Wash glazing and framework, then clean reusable pots. This removes places where pests and disease can persist.

Maximising your greenhouse space

Greenhouse space is always at a premium. These three techniques help you produce more from the same footprint.

Succession planting

Don't leave empty space after a crop finishes. As soon as you pull out the spring lettuce in May, plant your tomato grow bags in the same spot. When tomatoes finish in October, sow winter salad leaves immediately. A well-planned greenhouse is producing something 10-11 months of the year.

Vertical growing

Train cucumbers, cordon tomatoes and climbing beans upwards on secure supports. Hanging baskets suit strawberries and trailing tomatoes. Keep the central path clear and do not overload roof bars.

Companion planting

Grow compatible crops together when their water, light and temperature needs match. Flowers can support pollinating and predatory insects. They do not replace regular pest checks or biological controls.

Greenhouse accessories that make a difference

Start with equipment that helps you measure conditions and prevent avoidable crop losses.

You can find these in our accessories range. Call 0800 098 8877 for product and compatibility advice.

Common greenhouse growing mistakes to avoid

The same problems recur in customer questions each growing season:

1. Buying too small. Choose the largest size your space and budget allow. Leave enough room for paths, staging and mature plants.
2. Not ventilating enough. Trapped heat and humidity stress crops. Open vents early and check the thermometer during sunny weather.
3. Overwatering in winter. Plants need far less water when it's cold. Roots sitting in cold, wet compost rot quickly. Water only when the compost surface is dry.
4. Skipping the base. A level, secure base keeps the frame square. This helps doors and vents work correctly.
5. Planting too early. January tomato sowing needs reliable heat and strong light. Otherwise, wait until conditions improve in February or March.
6. Forgetting to feed. Container compost has limited nutrients. Follow the crop and fertiliser instructions once plants begin active growth.
7. Ignoring the autumn clean. Remove old crops and wash empty surfaces. This reduces places where pests and disease can persist.

Frequently asked questions

What is the best greenhouse for growing vegetables in the UK?

A 6x8ft aluminium greenhouse suits many first-time UK vegetable growers. Toughened glass gives high light and safer breakage. Polycarbonate retains more heat and resists impact, but transmits less light. Choose for your site, budget and household. Our greenhouse comparison guide explains the options.

When should I start planting in my greenhouse in the UK?

Use heat for January and February sowing. Hardy salads can start earlier than tender crops. Tomatoes, peppers and cucumbers need steady compost warmth. In an unheated greenhouse, wait for suitable local temperatures.

How do I stop my greenhouse overheating in summer?

Open the roof vents, side vents and door. Add the minimum shading needed to keep temperatures below 27°C. Water roots in the morning and damp hard paths when more humidity is useful.

Can I grow in my greenhouse all year round?

Yes, hardy crops can use an unheated greenhouse through much of winter. Growth slows when light levels fall. Summer crops need warmth and stronger light. Read our winter greenhouse guide before choosing crops.

What temperature should I keep my greenhouse at?

Most summer vegetables grow well between 18°C and 24°C. Keep temperatures below 27°C where possible. Tender seedlings need warmer compost than established hardy salads. Measure day and night conditions with a maximum-minimum thermometer.

Do I need to water my greenhouse plants every day?

Check greenhouse pots daily during warm weather. Water only when the crop and compost need it. Large plants in grow bags dry faster than deep borders. Reduce watering sharply during winter.

How do I pollinate plants inside a greenhouse?

Open vents and doors so insects can enter. Tomato flowers usually release pollen when gently tapped. All-female greenhouse cucumbers do not need pollination. Melons and squash may need hand pollination.

More growing guides from Greenhouse Stores

This guide covers the big picture, but we've written detailed growing guides for individual crops too. These go deeper into varieties, feeding schedules, common problems, and harvest timing: