Seed Starting Timeline
Fill in your own last frost date at the top, then count the days back. Everything here is relative to it.
BFCBrilliance · bfcbrilliance.com/tools/seed-starting-date-calculator
The arithmetic
- Sow, days before frost
- weeks x 7 − days after frost
- Emergence due
- sow day − germination days
- Harden off starts
- harden days − days after frost
- Negative means
- AFTER the frost date
- Grow-on window
- indoor days − germination − hardening
- ⚠ The frost date
- from YOUR met or extension service
- ⚠ It is a PROBABILITY
- not a guarantee for any one year
- ⚠ Weeks-before
- from YOUR seed packet
This sowing
- Crop and variety
- MY LAST FROST DATE
- Weeks indoors (packet)
- Germination days (packet)
- Hardening days
- Days after frost to plant out
- SOW ON
- EMERGENCE DUE
- HARDEN OFF FROM
- PLANT OUT ON
This season's sowings
| Crop | Sown | Up on | Hardened from | Planted out | How it did |
|---|---|---|---|---|---|
Through the timeline
- Frost date taken from a local source, not a national average
- Weeks-before read off THIS packet, not last year's crop
- Longer end of the germination range used for planning
- Days-after-frost set deliberately for tender crops
- Re-sown promptly if nothing emerged well past the due date
- Potted on before roots circle the cell
- Hardening off started on time, not skipped
- Soil temperature checked before planting tender crops out
- Dates and outcomes written down for next year
Early is the more expensive mistake
A seedling held indoors waiting for weather goes leggy and root-bound, and is often overtaken by one sown a fortnight later that went out at the right size. Sowing late costs some season; sowing early can cost the plant's whole constitution. When unsure, take the recoverable error.
A frost date is a probability
Published dates are usually the date by which frost has passed in a given proportion of years - not a promise about this one. Elevation, aspect and cold-air drainage all shift it locally, sometimes by more than the difference between two counties. Someone who has gardened your ground for years often knows the real version.