🌱🏡 What to Sow Indoors Each Month in the UK
🥕 Introduction: Why Indoor Sowing Matters in the UK
Sowing seeds indoors is one of the best ways to extend the UK growing season, protect young plants from unpredictable weather, and achieve earlier, stronger harvests. By starting seeds inside at the right time, gardeners can make the most of short summers and avoid losses from frost, wind, and heavy rain.
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This month-by-month guide explains what to sow indoors each month in the UK, helping you plan ahead and grow healthy vegetables from winter through to late summer.
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• Seed Trays & Module Pots
Ideal for indoor sowing and organised seed starting.
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• Heated Propagator
Helps improve germination during colder months.
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• Grow Lights
Prevents leggy growth during low-light periods.
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🌱 January – Slow and Careful Starts
Indoor sowing begins gently.
✔ chillies
✔ peppers
✔ onions (from seed)
✔ leeks
Strong light and gentle warmth are essential.
🌱 February – Building Momentum
More crops can be started indoors.
✔ tomatoes
✔ aubergines
✔ celery
✔ lettuce
✔ herbs
Daylight increases but warmth is still needed.
🌱 March – The Main Indoor Sowing Month
March is very productive indoors.
✔ tomatoes
✔ cucumbers
✔ courgettes (late March)
✔ brassicas (cabbage, cauliflower, broccoli)
✔ lettuce
Ventilation becomes important.
🌱 April – Transitional Sowing
Indoor sowing continues for tender crops.
✔ courgettes
✔ squash
✔ pumpkins
✔ sweetcorn
✔ basil
Hardening off begins late in the month.
🌱 May – Final Indoor Sowings
Only tender and fast-growing crops are started now.
✔ cucumbers
✔ courgettes
✔ sweetcorn
✔ basil
Most seedlings move outdoors this month.
🌱 June – Limited Indoor Sowing
Indoor sowing is minimal.
✔ basil
✔ coriander
✔ late lettuce
Outdoor sowing usually replaces indoor growing.
🌱 July – Heat-Sensitive Crops Indoors
Indoor sowing can help avoid summer stress.
✔ lettuce
✔ spinach
✔ spring onions
✔ herbs
Cool indoor conditions improve germination.
🌱 August – Preparing for Autumn
Indoor sowing resumes for cooler seasons.
✔ spinach
✔ winter lettuce
✔ spring onions
✔ pak choi
Shade and moisture are important.
🌱 September – Overwintering Begins
Seeds are started for winter growth.
✔ spinach
✔ winter lettuce
✔ spring onions
✔ chard
Growth slows as light reduces.
🌱 October – Protected Growing Only
Indoor and under-cover sowing continues.
✔ winter lettuce
✔ spinach
✔ rocket
Greenhouses and cold frames are ideal.
🌱 November – Minimal Indoor Sowing
Very limited sowing is possible.
✔ lettuce (under cover)
✔ rocket
✔ herbs (windowsill)
Growth is slow and steady.
🌱 December – Planning More Than Planting
December sowing is rare.
✔ herbs (windowsill only)
Focus shifts to planning and preparation.
❄️🌤️ Key Indoor Sowing Tips
✔ use clean compost
✔ avoid overwatering
✔ provide good light
✔ maintain steady temperatures
✔ harden off gradually before planting out
Good indoor care leads to stronger outdoor plants.
🌟 FAQs
Do I need heat to sow indoors?
Some seeds need warmth, especially early in the year.
Can I sow seeds on a windowsill all year?
Yes, but light levels and temperature must be suitable.
When should indoor seedlings be moved outside?
Only after hardening off and when frost risk has passed.
Is indoor sowing suitable for beginners?
Yes. It improves success and control.
Can I sow indoors without grow lights?
Yes, but light may be insufficient in winter months.