Seed packets often say "start indoors 6 to 8 weeks before the last frost". That is a count back from your last spring freeze date. This guide shows how to turn it into calendar dates.
The method
- Find your last spring freeze date: the historical date for your nearest NOAA station at the level you want (see the guide to what the probability levels mean).
- Look up the packet's weeks before last frost for each crop.
- Subtract: seven days per week. If your date is April 15 and the packet says 6 weeks, start on March 4.
- Pick a few days of leeway: seeds germinate at different speeds and your indoor space may run warmer or cooler.
Typical generic offsets
These are the planning defaults used in our products. They are central values, they differ among published guides, and every one is editable in the workbook.
- Onions from seed: about 8 to 12 weeks before the last freeze.
- Peppers and eggplant: about 8 to 10 weeks before.
- Broccoli, cabbage, cauliflower, kale: about 6 to 10 weeks before.
- Tomatoes: about 6 to 8 weeks before.
- Basil: about 4 to 6 weeks before.
- Melons: about 3 to 4 weeks before.
- Cucumbers and squash: about 2 to 3 weeks before.
Fast growers such as cucumbers and squash overgrow their pots when started too early, which is why they get the shortest lead.
Plant out after the cold window
Cool-season crops are often moved out a few weeks before the last freeze date, and warm-season crops after it, once nights have warmed. Hardening off plants gradually helps. These are habits, not rules; follow your seed packet and local extension office.
Choose your risk level
If a late freeze would end a crop, count from the later (cautious) spring date. If you can replant or cover plants, count from the median or the earlier date.
Keep a record
Write down the sowing date, the first sprout and the sprouted percentage. The Seed Starting Log spreadsheet works out days to sprout and sprouted percent for you.
The offsets count from a historical date; they are not a forecast and not agricultural advice.
Want the dates for your own station? See the Garden Calendars workbook and regional packs, or the free sample PDF. Next guide: Fall planting: counting back from your first fall freeze.
Please note. Historical 1991-2020 averages from NOAA; actual frost dates vary year to year; not a forecast or a guarantee; not agricultural advice. Planting windows are generic offsets from historical dates; follow your seed packet, your local extension office and the current weather forecast. This product is AI-assisted, so errors are still possible; please report them to gb1@mail.grokbot.com.
Source: Palecki, M., Durre, I., Applequist, S., Arguez, A., Lawrimore, J. (2021). U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020), version 1.0.1. NOAA National Centers for Environmental Information. doi:10.25921/4ek7-fk11. Quietcog is independent and is not affiliated with, endorsed by or sponsored by NOAA or the National Weather Service. Quietcog processed the station files; any processing errors are ours.
Support: gb1@mail.grokbot.com.