What this is
Eleven calculators for growing food and looking after a garden, covering frost dates and sowing schedules at one end and soil, compost, water and seed quantities at the other. They run entirely in your browser. Nothing you type is sent anywhere, there is no account, and there is no newsletter.
Where the numbers come from
Frost dates are median 0 °C / 32 °F dates by USDA hardiness zone. Median means half of years see a later frost, which is why every tool also quotes a safe date two weeks on. The maritime setting exists because zone numbers describe winter minimums and say nothing about summer heat, which makes them misleading for the UK, Ireland and the Pacific Northwest.
Crop timings — weeks under cover, weeks to planting out, days to maturity, spacing and crop water coefficients — are standard horticultural figures for common varieties. Variety matters: a short-season tomato and a beefsteak differ by five weeks and both are sold as "tomato".
Material quantities use straightforward geometry with the assumptions stated on each page. Where a figure is a working rule rather than a physical constant — mulch depth, waste allowances, heater duty cycle — the page says so and explains the reasoning, so you can substitute your own.
What it cannot do
It cannot tell you what will happen in your garden. Published frost dates come from weather stations in open ground, and a garden in a frost pocket, on a slope or against a south wall can differ by a fortnight in either direction. Every date tool has an adjustment field for exactly that reason — keep notes for a season and the site becomes considerably more accurate for you than any published table.
It is also not a substitute for a soil test. The pH calculator will tell you how much lime a given change needs; it cannot tell you what your soil currently is.
How it is funded
Advertising, and nothing else. There is no paid tier, no affiliate linking on the calculators, and no data sold — the calculators do not transmit what you enter, so there is nothing to sell. If advertising ever stopped covering the hosting, the honest thing would be to say so on this page rather than quietly change how the site works.
Corrections
If a figure here is wrong, I would genuinely like to know, particularly on the frost dates and crop timings where regional experience beats a published average. Email [email protected] with the page and what you think it should say. Corrections get made and the page updated.