About What To Sow

Every gardening site says the same thing: “sow tomatoes in March.” But March in Cornwall and March in Edinburgh are completely different. One has mild frosts behind it. The other has snow on the ground.

What To Sow fixes that. Enter your UK postcode and the tool calculates your local last frost date — then tells you exactly which crops to sow this week, based on where you actually are.

How it works

Your postcode is converted to a latitude, longitude, and elevation using Postcodes.io. From there, we estimate your last frost date using a model calibrated against Met Office climate averages. Altitude, latitude, and coastal proximity all factor in — a sheltered coastal garden in Devon gets a very different date from an exposed hilltop in the Pennines.

Real-time soil temperatures and frost forecasts come from Open-Meteo, which incorporates UK Met Office data. When we say there's a frost risk tonight, it's based on your actual forecast — not a rule of thumb.

How accurate is it?

Our frost date estimates are typically accurate to within 5–7 days. But frost dates are long-term averages — in any given year the actual last frost could be earlier or later. Microclimates matter too: a south-facing wall, a frost pocket, or an urban heat island can shift your conditions by a week or more. The tool gets you close. Your own observations get you the rest of the way.

Why it's free

Personalised planting advice shouldn't sit behind a subscription. The data is open, the tool is free, and it always will be. Some links on the site are affiliate links to seed suppliers — if you buy through them, we earn a small commission at no extra cost to you.

If the tool's been useful and you'd like to help keep it running, you can buy us a coffee. Completely optional — the site stays free either way.

Get in touch

Questions, feedback, or just want to say hello: [email protected]