What to plant in May in the Southwest

Worked out for 8 cities from their own weather and frost dates, by zone.

What to sow and plant in May in the Southwest, by zone: frost-free, highs of 72–82 °F (Albuquerque and Santa Fe (United States)): tomato, bell pepper, zucchini, green beans, cucumber and 23 more; frost possible, highs of 61–72 °F (Flagstaff): tomato, bell pepper, zucchini, cucumber, eggplant and 16 more.

In the Southwest, May is spring.

Frost-free, highs above 82 °F: Phoenix, Las Vegas, Tucson, Yuma and 1 more

In May, on average, these cities have highs of 87 to 96 °F and lows of 60 to 68 °F, 0.0 to 0.3 in of rain on 0 to 2 days; the day lasts 13 h 48 min to 14 h 04 min (on the 15th). A dry month: whatever is sown needs watering.

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 August	Celeriac, celery, chayote	Las Cruces

Compared with April: new — celeriac, celery and chayote; no longer sown — zucchini, green beans, basil, bok choy, borage and arugula.

Not starting in May: tomato (January, started indoors), bell pepper (January, started indoors), zucchini (September, sown direct), green beans (September, sown direct), lettuce (November, started indoors), peas (November, sown direct) and spinach (November, started indoors) — dates for Tucson.

Ready to harvest in May in Tucson, if sown in the right month: cabbage (January), green beans (March), bok choy (March), borage (March) and Napa cabbage (March).

Frost-free, highs of 72–82 °F: Albuquerque and Santa Fe (United States)

In May, on average, these cities have highs of 72 to 82 °F and lows of 47 to 53 °F, 0.7 to 1.2 in of rain on 4 to 6 days; the day lasts 13 h 59 min to 14 h 02 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	all
sow direct or start indoors, plant out in June	Zucchini, watermelon, pumpkin, basil, luffa, okra, peanut	all
sow direct	Green Beans, soybean	Albuquerque
start indoors, plant out in June	Cucumber, melon, achocha	all
sow direct	Sweet Corn, bok choy, borage, chayote, corn, Florence fennel, kiwano, Napa cabbage	all
sow direct	Arugula	Santa Fe (United States)
start indoors, plant out in August	Celeriac, celery	Albuquerque

Compared with April: new — green beans, borage, corn and soybean; no longer sown — peas, lettuce, radish, Swiss chard, beet, parsley, cilantro, chamomile and 3 more.

Not starting in May: lettuce (September, started indoors), peas (September, sown direct) and spinach (September, started indoors) — dates for Santa Fe (United States).

Ready to harvest in May in Santa Fe (United States), 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: Flagstaff

In May, on average, Flagstaff has highs of 71 °F and lows of 45 °F, 0.9 in of rain on 6 days; the day lasts 14 h 00 min (on the 15th). A dry month: whatever is sown needs watering.

May falls in the frost season: frost-tender crops wait. Average last frost: Flagstaff (May 5).

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

Compared with April: new — zucchini, cucumber, melon, watermelon, pumpkin, sweet corn, basil, achocha and 6 more; no longer sown — peas, lettuce, radish, Swiss chard, beet, parsley, cilantro, celeriac and 6 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 Flagstaff.

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

Frost dates in Flagstaff

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.