Planting calendar tool

Pick a pilot city or type your own frost dates. The tool applies the same cited extension rules as the city pages and shows every assumption it makes.

1. Frost dates

Pilot city (NOAA station) Last spring frost (MM/DD) First fall frost (MM/DD)

Where to find yours: NOAA's U.S. Climate Normals 1991–2020 publish the 50% probability last-spring and first-fall 32°F dates for thousands of stations. Your county extension office usually quotes the same figures.

2. Crops

Crop	Frost class	Start seeds indoors	Plant outdoors	Last fall planting	Days to harvest

Assumptions. Hardy crops: 2–4 weeks before last frost. Semi-hardy: 0–2 weeks before. Tender: on the frost date to 1 week after. Very tender: 2–4 weeks after (Colorado State Extension GardenNotes #720). Indoor start = outdoor window minus the transplant age from the same guide. Last fall planting = first fall frost minus days to harvest, plus a 14-day allowance for hardy and 7-day for semi-hardy crops, which is our editorial assumption, not the source's. Full detail on the methodology page.

How the planting calendar tool works

The tool needs only two numbers: the date after which a 32°F reading is no more likely than not in spring, and the date before which it is no more likely than not in fall. Both come straight from NOAA's 1991–2020 normals for a named station. Everything else is arithmetic on published rules, which is why the page can show every step.

It does not know your microclimate. A garden in a frost pocket or on a north slope can run a week or two behind the airport. The Colorado State guide says soil temperature is one of the best signals for spring planting, so for warm-season crops check a soil thermometer as well as the calendar.

For the reasoning behind using frost dates rather than zones, read last frost date vs hardiness zone. For a ready-made version of this output for 40 cities, see the calendars by city.