When Does The Growing Season Start in the UK? (And When Does It End?)
It sounds like a simple question, doesn't it? well it ain't...
"When does the growing season start?" Ask five gardeners and you'll get six different answers.
The truth is - there's no single hard date. It all depends on what you mean by "growing" and exactly where your patch is in the country. Here's the honest, no-nonsense guide from my garden in Tonbridge.
The Official Definition - The "Thermal" Season
The Met Office has a proper definition for it. They call it the thermal growing season:
Starts: 5 days in a row where the average temperature is above 5°C
Ends: The day before 5 days in a row drops below 5°C again
Average for the UK: About 240 days - early March to mid-November
So technically, down here in the south it never really stops! But just because it's above 5°C doesn't mean your tomatoes are happy. That's bare-minimum, barely-keeping-alive growth. Not thriving.
The Gardener's Real Definition - Frost-Free Days
For us lot with seedlings in trays, the season is really:
Last frost in spring → First frost in autumn
Because frost is what kills things. It can be 10°C in the day and -2°C at 3am - your courgettes are toast. And this is where it changes a lot depending on where you live:
Inner London / South Coast: Last frost early March, first frost late November - about 8 months
South East (Kent - hello! - us): Last frost mid to late April, first frost early November - about 6.5 months
Midlands / East Anglia: Last frost mid to late April, first frost early November - about 6 months
Wales / Northern England: Last frost late April to early May, first frost late October - about 5.5 months
Scottish Lowlands: Last frost late April to mid May, first frost late October - about 5 months
Scottish Highlands: Last frost mid to late May, first frost mid to late October - about 4 months
For us in Tonbridge / Kent: Roughly mid-April to early November. But don't trust it blindly - we've had frost in May and in October here before!
The Three Stages - It Doesn't Just Switch On
It doesn't flip like a light switch. It comes in stages:
Early - Feb to March
Soil thaws, worms wake up, weeds pop through. Hardy stuff goes in - broad beans, garlic, onions, early peas, salad leaves. Soil is still cold, not safe for tender stuff yet.
Main Season - April to October
The real deal. Soil is properly warm, nights are mild, days are long. Once that last frost has passed - courgettes, beans, tomatoes, cucumbers go out. Everything grows like mad.
Late / Overwintering - Nov to Feb
Growth slows right down but doesn't always stop. Kale, winter salads, onions, broad beans just sit there waiting. Garlic quietly puts roots down under the soil.
Soil Temperature - The Secret That Actually Matters
Frost dates are a good guide, but soil temperature is what really counts. Seeds won't germinate until the ground is warm enough:
5-6°C: Broad beans, peas, onions, lettuce will start
10°C: Beetroot, carrots, spinach
12-15°C: Tomatoes, cucumbers, courgettes, runner beans
15°C+: Sweetcorn, pumpkins, melons
A cheap £6 soil thermometer is the best tool I own. Stick it in 10cm deep at 9am. Way more reliable than any calendar.
What About The Dates On Seed Packets? My Take.
Here's the bit they don't put on the packet. Those sowing dates - "Sow March to May" - they were written 20 years ago when seasons were proper seasons.
Back in the day, it WAS controlled by the months. You sowed broad beans in February because it was always cold in February. You planted out runner beans at the end of May because you KNEW the frost was gone.
Now? It's all over the place. We had 18°C in February this year, then frost in late April.
So I don't go by the months anymore, I go by the actual weather.
If the packet says "sow outdoors March" but the soil is still 4°C and soaking wet, I don't sow. I wait. If it says "plant out May" but we are having a cold, wet May and soil is 8°C, my tomatoes stay in the greenhouse.
Use the packet as a rough guide, but use your thermometer and the forecast as the real decision maker. The plant doesn't know what month it is - it only knows if it's warm enough and wet enough.
It's Getting Longer - Fact
Because winters are warmer, the UK growing season is about a month longer than it was in the 1960s. Starts earlier, finishes later. Brilliant for us, but pests and diseases stick around longer too. Nothing's ever simple, is it?!
My Working Rule For Tonbridge
Early March - things start waking up.
Mid-May - safe to plant out tender stuff IF the forecast looks kind.
October - start thinking about frost.
November - wind it down and plan next year.
But always - ALWAYS - check the 7-day forecast. One late frost in May or an early one in October can undo weeks of work in one night. Keep that fleece handy!
Over to you - when do you reckon the season starts where you are? Been caught out by a surprise frost? Drop a comment below, I'd love to hear your local markers.
Happy gardening - and make the most of every day!
Digger Dave The Messy Gardener, Kent
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