Planting Calendar Generator
Seed packets say things like 'sow six weeks before the last frost', which is only useful once you know when your last frost is. Everything in a growing year is measured from that date rather than from the calendar — which is why the same crop goes out weeks apart in different places. This works every date back from the two frost dates you give it, and says plainly which crops will not ripen in the season you have.
What this generator does
Takes your last and first frost dates, works out the growing season between them, and calculates each crop's sowing, planting-out and first-harvest dates as offsets from the last frost — flagging any crop whose harvest would fall after the first frost.
How to use this tool
- Enter your local average last and first frost dates.
- Read the sowing, planting-out and harvest dates for each crop.
- Check the growing season length against the crops that need the longest.
- Anything flagged as too late needs an earlier start under cover, or a faster variety.
Understanding the controls
- Last frost
- Your local average last frost of spring. Every date is measured from this, which is why the calendar moves with your location rather than the month.
- First frost
- Your local average first frost of autumn. The gap between the two is your growing season.
- How many crops
- Between 3 and 9, drawn from common vegetables with realistic timings.
- Seed
- Any word reproduces exactly the same crops and dates.
Common use cases
- Planning a season's sowing from your own frost dates
- Working out whether a long-season crop is realistic where you are
- Understanding why sowing advice is always relative to frost
- Building a personal calendar rather than following a generic one
- Setting the same plan twice from a seed
How this generator works
Dates are computed in whole days from the last frost, so leap years and month lengths look after themselves. The check enforces the order of operations rather than just the arithmetic: a crop can never be planted out before it is sown, nor harvested before it is planted out, and every date must genuinely be the stated number of days from the frost.
Randomness and fairness
Which crops appear is random; every date is a deterministic offset from the frost dates you enter. A seed reproduces the same selection exactly and is therefore explicitly not cryptographically secure. Without a seed the browser's cryptographically secure generator is used.
For how randomness is produced across the whole site, see how Generate Random works.
Limitations and good to know
- Frost dates are averages, and a late frost after the average one is exactly the risk that catches people out.
- Timings are typical for the crop rather than for a specific variety, which can differ by several weeks.
- Soil temperature, day length and rainfall all matter and none is modelled.
- Northern-hemisphere assumptions about season order, though the arithmetic itself is direction-agnostic.
- Calendars are not stored between visits; seed one you want again.
Privacy and your data
The calendar is computed in your browser. Neither your frost dates nor your seed is transmitted or stored.
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