Greenhouse Growing Calendar: What You Can Grow Month-by-Month in the UK

There is a particular kind of magic to stepping into a greenhouse in a UK winter, especially when following a greenhouse growing calendar.

While the rest of the garden is cold, wet, and lifeless, inside it’s calmer. The air is still. The soil smells damp rather than frozen. Even in January, it feels like something could grow.

That’s what a greenhouse really gives you in the UK: time.
Not just protection from frost, but the ability to stretch the growing season at both ends — even with a small, unheated setup.

This guide serves as your greenhouse growing calendar, showing what you can realistically grow in a UK greenhouse throughout the year, broken down by season, with practical notes on unheated vs heated greenhouses and where different greenhouse types fit best.

❄️ Winter (December – February)

Survival, protection, and quiet preparation

Winter greenhouse growing in the UK is about protecting what you have, not forcing growth. This is where even a basic structure — such as a small greenhouse — proves its value by keeping plants dry, frost-free, and alive.

December – Rest & Maintenance

What’s realistic

• Harvesting winter salads
• Lamb’s lettuce, spinach, pak choi (slowly)
• Microgreens with some heat

Growth is minimal without heating, but December is ideal for:

• cleaning glazing
• checking seals
• planning next year’s layout

If you want to grow more than just hardy greens at this time of year, this is where learning how to heat a greenhouse safely and efficiently starts to matter.

January – Protection Over Progress

What you can maintain

• Established winter salads
• Spinach
• Parsley and chives (very slow)

January kills plants through cold, wet compost, not frost. Water sparingly and focus on insulation.

Grower insight:
In January, more greenhouse plants die from damp feet than from the cold. If compost stays soggy for days, roots simply give up. Only water on a bright morning so leaves and soil have time to dry before nightfall. If you’re gardening in a small or lean-to greenhouse, winter highlights just how effective sheltered, wall-backed structures can be for temperature stability.

February – The First Signs of Life

Light levels slowly improve, and optimism creeps in.

What you can sow

• Broad beans (in pots)
• Onions from seed
• Early lettuce
• Spinach
• Peas (to transplant later)

With even a small amount of heat:

• Chillies
• Peppers
• Aubergines

This is where mini greenhouses really shine — they warm quickly on bright days and are ideal for early sowing without heating a large space.

🌱 Spring (March – May)

The real growing season begins

Ventilation, frost awareness, and choosing the right type of greenhouse matter more now than at any other time of year.

March – The UK “Trap Month”

March looks like spring. It often isn’t.

What to sow

• Tomatoes
• Cucumbers
• Courgettes
• Lettuce and salad mixes
• Kale
• Basil (with warmth)

Warm afternoons followed by freezing nights are common. Keep fleece nearby and cover plants before sunset.

Grower insight:
March is when many growers realise why small and medium greenhouses are so popular — they’re large enough for trays and pots, but still easy to protect overnight.

April – Growth Accelerates

Days are longer, and plants respond quickly.

What thrives

• Tomatoes
• Cucumbers
• Peppers
• Aubergines
• Strawberries (pots or grow bags)
• Salad crops

Ventilation becomes critical now. On sunny days, greenhouses can overheat even when nights are cold.

If you’re deciding between structures, April makes the differences clearer — something explored in more depth when comparing greenhouses vs polytunnels for spring growing.

May – Main Season Starts

This is where greenhouses earn their keep.

What thrives

• Tomatoes
• Cucumbers
• Chillies and peppers
• Melons
• Basil and tender herbs

Watering and feeding routines now matter more than equipment. Consistency beats intensity.

☀️ Summer (June – August)

Harvests, heat, and airflow

Summer greenhouse growing is less about warmth and more about control.

June – Fruiting & Feeding

What to grow

• Fruiting tomatoes
• Cucumbers
• Peppers and chillies
• Aubergines
• Grapes

Good airflow prevents disease. Don’t let lush growth block vents or doors.

Grower insight:
Larger greenhouses and polytunnels handle airflow better in summer, especially if you’re growing multiple fruiting crops at once.

July – Heat Management

Greenhouses can exceed 40°C surprisingly early in the day.

Focus on

• Harvesting
• Late sowings of lettuce
• Herbs
• Dwarf French beans

Pro tip
If you don’t have automatic vents, try damping down — literally splashing a few watering cans of water over the floor paths. As it evaporates, it creates a cooling mist that helps stop tomatoes and cucumbers wilting in the midday sun.

August – Transition Month

Still productive, but nights begin to cool.

What to sow

• Spinach
• Rocket
• Winter lettuce
• Pak choi
• Spring cabbage (for overwintering)

This is also a good moment to assess whether a polytunnel would suit you better for extended autumn and winter cropping.

🍂 Autumn (September – November)

Tidying, protection, and winding down

Autumn greenhouse success depends on how tidy and ventilated things are now.

September – Cooling Down

What still works

• Salad leaves
• Spinach
• Oriental greens
• Herbs (slowly)

Clear out tired summer plants early. Space and airflow reduce disease later.

October – Insulate & Tidy

What still grows

• Winter lettuce
• Spinach
• Lamb’s lettuce
• Spring onions

Grey mould loves damp UK autumns. Removing dead leaves now saves headaches in November.

If you plan to keep growing, October is the month to revisit greenhouse heating options — even minimal frost protection makes a big difference.

November – Survival Mode

Growth slows dramatically.

Focus on

• Harvesting
• Insulation
• Cleaning glazing to maximise light

This is the final checkpoint before winter sets in fully.

Unheated vs Heated Greenhouse – A Simple UK Decision Guide

Most UK growers start with an unheated greenhouse — and that’s absolutely fine.

If you find yourself frustrated that:

• chillies can’t be sown until April
• winter salads stall completely

that’s usually when learning how to heat a greenhouse becomes worthwhile, even if it’s just frost protection.

📅 Want Monthly Greenhouse Reminders Instead of Guessing?

If you’d like gentle prompts through the year, you can download the UK Greenhouse Growing Calendar and add it to Google Calendar, Apple Calendar, or Outlook.

It includes simple reminders like:

• “Start early sowing under cover”
• “Ventilate on warm days”
• “Begin autumn sowing”

⚠️ Calendar Disclaimer

This calendar is designed as a prompt, not a replacement for this guide.

UK weather, greenhouse size, and location vary.
Always check the full seasonal notes above before sowing or harvesting.

Final Thoughts

A greenhouse doesn’t just change what you grow — it changes when you grow.

Whether you’re using a compact mini greenhouse, a lean-to, or a full-size structure, understanding the seasonal rhythm is what turns a greenhouse from a shelter into a system.

For more guidance on greenhouses, we recommend this post from the RHS on Growing in Greenhouses.

🔗 Related Greenhouse Guides

• Greenhouses and Polytunnels UK – Complete Guide
  A full overview of greenhouse and polytunnel options, including comparisons, setup advice, and buying guides for UK gardens.
• How to Use a Greenhouse
  Practical guidance on ventilation, watering, temperature control, and day-to-day greenhouse use throughout the year.
• What Is the Best Type of Greenhouse?
  A clear breakdown of greenhouse styles, materials, and designs to help you choose the right option for your garden.