How it works

Frost dates

Frost dates are from the NOAA U.S. Climate Normals for 1991–2020, which give the probability of a 32°F freeze at each weather station. We use:

• Typical last spring frost: the date after which there's a 50% chance of another freeze.
• 9-in-10 safe date: the date after which there's only a 10% chance.
• Typical first fall frost: the date by which there's a 50% chance of the first freeze.

Most stations are at airports. Airports in valley bottoms can run colder than nearby hillsides, and city centers can run warmer. Your own garden may differ by a week or more.

Planting dates

Each crop gets the later of two dates:

1. A regional date for when the soil is usually ready, taken from Oregon State University Extension's March, April and May garden calendars, its Central Oregon vegetable calendar, and its soil temperature guidance. Washington areas use the closest matching Oregon region.
2. A frost check against your local typical last frost: hardy early crops up to 6 weeks before it, frost-tolerant transplants up to 4 weeks before, warm-season transplants not before it, and warm-season seeds a week after it.

Seed-starting dates count back from the outdoor date (for example, tomatoes 6–8 weeks ahead). Fall planting dates count back from your typical first fall frost, capped at October 15 because fall crops need daylight to grow, not just mild weather. Warm-season crops are flagged when planting at the window's start leaves too few days before fall frost for a typical variety to produce.