Question 1

Will the ICS file really work with Google Calendar and Apple Calendar?

Accepted Answer

Yes. The file uses the standard RFC 5545 iCalendar format, which is what Google, Apple, and Outlook all use natively. Google Calendar: import via Settings → Import & export. Apple Calendar: double-click the .ics file. Outlook: File → Open & Export → Import/Export. All 40+ events get added as all-day entries on the right dates, with emoji in the title so they're easy to spot.

Question 2

Where does the last-frost date come from?

Accepted Answer

It's computed fresh for your ZIP from the last 15 years of daily temperature records. The tool looks up your ZIP's lat/lng, pulls 15 years of daily minimums from the ECMWF ERA5 reanalysis, finds the last spring day in each year that hit 32°F or below, and averages those dates. That's the 50th percentile last-frost date. It automatically reflects recent warming because it always uses the most recent 15 years.

Question 3

Does this handle fall plantings too?

Accepted Answer

Not yet. This tool focuses on the spring seed start window because that's where planning leverage is highest. Fall plantings depend on the FIRST frost date and season length, which is a separate calculation. A fall succession planner is on the roadmap.

Question 4

Why does it suggest hardening off a week before transplant?

Accepted Answer

Seedlings raised indoors have soft, thin cuticles and no UV-adaptation. Moving them straight from a windowsill to full sun typically kills half the leaves and stunts growth for 2-3 weeks. Hardening off means putting them outside in shade for an hour or two, then gradually lengthening the time and exposure over 7-10 days. This tool schedules a harden-off reminder exactly a week before each transplant date so you don't skip the step.

Question 5

My zone is 6b but I'm in a frost pocket. Should I adjust?

Accepted Answer

Yes, by about 1-2 weeks. Frost pockets (low-lying areas where cold air settles overnight) typically see last frost 10-14 days later than the ZIP average, and first frost 10-14 days earlier. If you know you're in a frost pocket, treat every transplant date in this calendar as being ~2 weeks too early and adjust. South-facing slopes and urban heat islands work in the opposite direction: you can safely subtract a week.

Seed Start Calendar

Common questions

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