What to plant in May in the Pacific Northwest

Worked out for 11 cities from their own weather and frost dates, by zone.

What to sow and plant in May in the Pacific Northwest, by zone: frost-free, highs of 72–82 °F (Boise and Yakima): tomato, bell pepper, zucchini, green beans, cucumber and 20 more; frost possible, highs of 61–72 °F (Idaho Falls): radish, tomato, bell pepper, zucchini, cucumber and 17 more; frost-free, highs of 61–72 °F (Seattle, Portland and 6 more): peas, radish, beet, tomato, bell pepper and 28 more.

In the Pacific Northwest, May is spring.

Frost-free, highs of 72–82 °F: Boise and Yakima

In May, on average, these cities have highs of 73 to 77 °F and lows of 48 to 50 °F, 0.6 to 1.7 in of rain on 4 to 8 days; the day lasts 14 h 42 min to 15 h 00 min (on the 15th).

No frost in May in 10 years of data: frost-tender crops can go in too, if it is warm enough for them.

How	What	Where
start indoors, plant out in July	Tomato, bell pepper, eggplant, chili pepper, moringa	Yakima
start indoors, plant out in June	Zucchini, cucumber, melon, watermelon, pumpkin, basil, achocha, luffa, okra, peanut	Yakima
sow direct	Green Beans, arugula, bok choy, borage	all
sow direct	Sweet Corn, chayote, corn, Florence fennel, kiwano, Napa cabbage	Yakima

Compared with April: new — green beans, borage and corn; no longer sown — peas, lettuce, radish, Swiss chard, beet, parsley, cilantro, chamomile and 5 more.

Not starting in May: lettuce (October, sown direct), peas (October, sown direct) and spinach (October, sown direct) — dates for Boise.

Ready to harvest in May in Boise, if sown in the right month: peas (March), spinach (March), lettuce (March), radish (April), Swiss chard (March), arugula (April), chamomile (March) and daikon (March).

Frost possible, highs of 61–72 °F: Idaho Falls

In May, on average, Idaho Falls has highs of 69 °F and lows of 42 °F, 1.7 in of rain on 9 days; the day lasts 14 h 41 min (on the 15th).

May falls in the frost season: frost-tender crops wait. Average last frost: Idaho Falls (May 11).

How	What	Where
sow direct	Radish, arugula	Idaho Falls
start indoors, plant out in July	Tomato, bell pepper, eggplant, chili pepper, Florence fennel, moringa	Idaho Falls
start indoors, plant out in June	Zucchini, cucumber, melon, watermelon, pumpkin, sweet corn, basil, achocha, bok choy, kiwano, luffa, Napa cabbage, okra, peanut	Idaho Falls

Compared with April: new — zucchini, cucumber, melon, watermelon, pumpkin, sweet corn, basil, achocha and 6 more; no longer sown — peas, lettuce, Swiss chard, beet, celeriac, celery, chamomile, chayote and 3 more.

Not starting in May: green beans (June, sown direct), lettuce (September, started indoors), peas (September, sown direct) and spinach (September, started indoors) — dates for Idaho Falls.

Ready to harvest in May in Idaho Falls, if sown in the right month: radish (April), arugula (April), dill (April) and mustard greens (April).

Frost dates in Idaho Falls

Frost-free, highs of 61–72 °F: Seattle, Portland, Spokane, Salem and 4 more

In May, on average, these cities have highs of 65 to 70 °F and lows of 42 to 48 °F, 2.0 to 3.2 in of rain on 8 to 13 days; the day lasts 14 h 35 min to 15 h 07 min (on the 15th).

No frost in May in 10 years of data: frost-tender crops can go in too, if it is warm enough for them.

How	What	Where
sow direct	Broad bean, cabbage, chickpea	Seattle and Olympia
sow direct	Peas, beet, sweet corn, parsley, cilantro, arugula, bok choy, borage, chamomile, chayote, corn, dill, Florence fennel, mustard greens, Napa cabbage	all
plant sets	Onion, shallot	Seattle and Olympia
sow direct	Lettuce, Swiss chard, kohlrabi	Seattle, Olympia and Tacoma
sow direct	Radish	Seattle, Portland, Salem and 4 more
start indoors, plant out in June	Cauliflower	Seattle
start indoors, plant out in July	Tomato, bell pepper, eggplant, chili pepper, moringa	all
start indoors, plant out in June	Zucchini, cucumber, melon, watermelon, pumpkin, basil, achocha, kiwano, luffa, okra, peanut	all
start indoors, plant out in August	Celery	Seattle, Portland, Salem and 2 more
start indoors, plant out in August	Celeriac	Portland, Salem and Tacoma
start indoors, plant out in July	Brussels Sprouts	Seattle

Compared with April: new — borage and corn; no longer sown — spinach, carrot, broccoli, daikon, kale and parsnip.

Not starting in May: green beans (June, sown direct) and spinach (September, started indoors) — dates for Portland.

Ready to harvest in May in Portland, if sown in the right month: peas (March), spinach (March), lettuce (March), radish (April), carrot (March), Swiss chard (March), beet (March) and arugula (April).

How we work it out

For each city we use its average weather in May and the months after (highs, lows and rain for 2016–2025, ERA5 reanalysis via Open-Meteo) and its average frost dates. A crop starts in May if the month's mean temperature reaches the minimum soil temperature for germination on its card (we use the mean air temperature as a stand-in for the soil's) and if, over its first months (up to three), the average highs stay within its group's range, with no frost for crops that cannot take it. Crops started indoors count from the month they are planted out.

Temperature groups from Colorado State University Extension: cool-season crops prefer 60–80 °F and lose quality in heat; hardy ones grow in days as cool as 40 °F, semi-hardy ones from 40–50 °F (we use 50 °F); warm-season crops need days above 55 °F, and the most tender (tomato, pepper, eggplant, melon, watermelon, squash) above 60 °F, up to 95 °F. Crops the guide does not name go into the stricter group by their frost hardiness. Fava (broad) beans, which the guide does not name, count as hardy: hardy varieties are sown in fall and overwinter (RHS). Garlic and bulbs: a month before the first frost, and later only while the ground is not frozen (as on each city's page).

This is a general rule from averages: your garden can be a week or two earlier or later, and a greenhouse or a cold frame brings the season forward. Greenly works out the dates for your location.