If you’ve ever lost a tray of seedlings to a surprise late frost, you’ll know just how costly getting the timing wrong can be. The trouble with national frost date guides is that they’re based on regional averages — and Surrey / Hampshire’s weather is far more varied than most people realise.
At Crondall Weather, we’ve been recording temperature data continuously since February 2006 from our Davis Vantage Pro2 weather station in the heart of the village. That means we can give you something no generic gardening website can: real, hyperlocal frost data for North Hampshire and the surrounding area, covering Crondall, Farnham, Fleet, Alton, Hook, and the wider Hart district.
Click here for our latest frost data.
Here’s everything you need to know to stop guessing and start planting with confidence.
What Is a “Last Frost Date” and Why Does It Matter?
A frost occurs when the air temperature drops to 0°C or below at ground level. Even a brief dip can kill off tender seedlings, damage newly planted vegetables, and ruin early-flowering plants that have been brought outside too soon.
The last frost date is the final date in spring when a frost is statistically likely to occur. It’s not a guarantee — weather is never perfectly predictable — but it gives you a solid, evidence-based baseline for planning your growing season.
Most gardening books quote a single date for “southern England” or “the South East.” That’s not good enough. A sheltered garden in a Farnham suburb behaves very differently from a frost pocket in a North Hampshire valley bottom.
Last Frost Dates for Crondall and North Hampshire
Based on our station records, here is how frost risk breaks down across the spring months in and around Crondall:
| Month | Average Low(°C) | Average Frost Days | Max Frost Days | Frost Risk | Verdict | |
| January | 1.0 | 13 | 21 | Very High | No outdoor planting | |
| February | 1.6 | 10 | 17 | High | Cold frames only | |
| March | 1.8 | 10 | 16 | Moderate-High | Sow under cover | |
| April | 3.1 | 7 | 18 | Low-Moderate | Harden off only | |
| May (early) | 4.4 | 2 | 6 | Low | Most tender plants safe | |
| May (late) | 8.4 | 0.5 | 4 | Very Low | Safe to plant out |
Our recommended last frost date for the Crondall area: around 10–15 May, with confidence that the risk is very low after the 20th.
The “Safe Planting Window” — What It Means for Your Garden
Most gardeners aim to plant out tender crops — tomatoes, courgettes, cucumbers, French beans, basil — only once they’re confident frost is behind them. Here’s a practical breakdown for the North Hampshire growing calendar:
🌱 March: Sow Indoors, Not Out
In March, overnight temperatures across Crondall regularly dip below 2°C with 10 days on average below freezing. This is a month for:
- Sowing tomatoes, peppers, and aubergines on a warm windowsill or heated propagator
- Starting off onion sets and early potatoes in bags in a frost-free shed or greenhouse
- Sowing sweet peas and hardy annuals under glass
🌷 April: Harden Off, But Stay Alert
Safe April activities include:
- Planting out hardy brassica seedlings (cabbage, cauliflower, kale) with cloche protection
- Sowing carrots, parsnips, beetroot, and salad leaves directly into the ground
- Planting first early potatoes (keep soil earthed up against frost)
- Planting summer-flowering bulbs like dahlias in containers you can bring inside if frost is forecast
🌻 May: The Green Light — With Caveats
- Tomatoes, courgettes, cucumbers, French and runner beans
- Basil and tender herbs
- Bedding plants and summer container displays
- Sweet corn
Frost Pockets: Why Your Garden Might Frost Later Than Ours
Our weather station is sited on Pankridge Street backing onto the 4 acre field (exact location is here).
If your garden is in a valley bottom, behind a solid fence that traps cold air, or in a low-lying area near the River Hart, you may experience frost one to two weeks later than our data suggests.
Cold air is heavy — it flows downhill and pools in low spots, much like water. This is why sheltered valley gardens in areas like the Whitewater or Hart river corridors can experience sharp ground frosts well into May, even when nearby elevated gardens are perfectly frost-free.
Practical tip: Lay a maximum/minimum thermometer at ground level in your own garden for a season. Your personal data will quickly reveal whether you’re in a frost pocket or a relatively warm spot.
How to Protect Plants From Late Frosts
Even when you follow the calendar correctly, a late cold snap can still happen. Here’s how to protect your plants quickly when a frost is forecast:
Your Secret Weapon: Live Frost Forecasts
The best gardening tool we offer isn’t in any catalogue — it’s our live temperature forecast probability, updated continuously from our Davis Vantage Pro2 station and supplemented with met-office model data.
Before any planting decision, check:
- Tonight’s minimum temperature forecast — anything below 2°C warrants covering tender plants
- 7-day temperature trends — a cold snap following a warm spell is when frost catches gardeners out
- Historical monthly minimums — available on our statistics pages
Bookmark our Latest Forecasts page and check it regularly through April and May. It costs nothing and could save you a season’s worth of work.
Data in this article is drawn from continuous temperature records collected at Crondall Weather Station, Crondall. Station equipment: Davis Vantage Pro2, Solar and UV sensor suite – full spec is here
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