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.

A frost here means 32°F, which damages tender crops like tomatoes and basil. A hard freeze, about 28°F or colder, is what finally stops hardy crops like kale and cabbage.

47 of the 86 towns use a station at an airport. 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.

How we pick each town's station

Rainline Garden covers 86 towns: 35 in Oregon, 36 in Washington and 15 in Idaho. Each one gets its own NOAA weather station rather than a state or regional average, and its page names that station, how far it is from town and how high it sits.

• Closest first. 60 of the 86 towns use the closest weather station that has NOAA's 1991–2020 frost records. We checked every station within 20 miles of each town.
• Sometimes another one. The other 26 use a different station nearby, and their pages say how far away it is.
• Local quirks noted. Where a nearby station is known to run warmer or colder than town, such as the airports at Portland and Pocatello, the town's page says so.
• No guessing. Where no station has frost records close enough, such as the Wood River Valley around Hailey and Ketchum, we leave the area out rather than borrow dates from a town with different weather.

West and east of the rain line

West of the rain lineEast of the rain line

The Cascades split the region in two. West of the mountains (the coast, the Willamette Valley, Puget Sound and the southern Oregon valleys), winters are wet and mild and summers are dry, usually from July until the fall rains return in October. East of the mountains, in the rain shadow that stretches across eastern Oregon and Washington and on into Idaho, rain is scarce all year, summers are hot and winters are colder. My garden plan uses your side of the line for its watering reminders: west-side plans get a reminder to start watering in early July and to ease off in mid October; east-side plans get one in early June and another at the end of September.

Planting dates

Each crop gets the later of two dates:

1. A regional date for when the soil is usually ready, based on typical soil warming in each climate region (the table below lists them). Washington and Idaho towns use the closest matching 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, warm-season seeds and heat lovers like peppers, eggplant, melons and basil 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.