Build a sowing window from your own dates
Use a local reference date and the growing interval from your seed packet. The calculator counts backwards; it does not decide when your garden is safe to plant.
Use a reference for your location and its stated risk level, then check the packet and forecast. The six-week and fourteen-day values are editable examples.
How this works, and what it leaves out
Sowing date = planned planting date − your indoor growing interval. Hardening begins within that interval, not as extra days added afterwards. The planting offset is your crop-specific decision; negative values can represent suitable hardy crops. Local freeze averages are historical probabilities, not a forecast. Air and soil temperatures, cultivar requirements, light and protection still govern planting.
University of Minnesota: seed-starting and hardening off ↗
Find the NOAA U.S. freeze-date map and understand its limits ↗
How to use this tool
- Choose a local spring freeze reference date and understand the probability or risk level attached to it.
- Use the planting offset to set your intended outdoor planting date before or after that reference, as appropriate for the crop.
- Enter the indoor growing interval from the seed packet and the hardening period within it. Then review the calculated dates against actual growing conditions.
Count six weeks back from a planned planting date
With a 15 May reference, a zero-day offset, six weeks from sowing to planting and a fourteen-day hardening period, the planned dates are 3 April for sowing, 1 May to begin hardening and 15 May for planting. These are arithmetic examples, not recommended dates for an unnamed crop or region.
What the result means
Hardening is included inside the sowing-to-planting interval. The tool does not add it afterwards. A positive offset moves the planting plan later; a negative one moves it earlier. An average freeze date describes historical risk, while the forecast, soil temperature, crop and available protection still determine whether your plan makes sense.
Questions before you start
Will the calculator find my local last frost date?
No. You supply the local reference. The NOAA link below explains U.S. historical freeze maps; use a suitable local source for other regions and check the risk level behind the date.
Should I start every seed indoors six weeks early?
No. Six weeks is an editable example. Some crops are direct-sown, and indoor growing intervals vary. Follow the packet or a reliable crop-specific guide before entering the interval.
Put it in context
Use these guides alongside the tool for the choices a calculation or decision form cannot make for you.