GreenlyWhat to plant in May in the Mountain West
Worked out for 15 cities from their own weather and frost dates, by zone.
What to sow and plant in May in the Mountain West, by zone: frost-free, highs of 72–82 °F (Salt Lake City, Reno and 2 more): tomato, bell pepper, zucchini, green beans, cucumber and 20 more; frost-free, highs of 61–72 °F (Billings, Fort Collins and 1 more): tomato, bell pepper, zucchini, cucumber, eggplant and 19 more; frost possible, highs of 61–72 °F (Denver, Colorado Springs and 5 more): peas, radish, beet, tomato, bell pepper and 22 more.
In the Mountain West, May is spring.
Frost-free, highs above 82 °F: St. George
In May, on average, St. George has highs of 85 °F and lows of 58 °F, 0.2 in of rain on 2 days; the day lasts 14 h 08 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.
By these rules no garden crop starts in May in St. George.
Compared with April: no longer sown — green beans, arugula, bok choy and borage.
Not starting in May: tomato (no month outdoors by these rules), bell pepper (no month outdoors by these rules), zucchini (September, sown direct), green beans (September, sown direct), lettuce (October, started indoors), peas (October, sown direct) and spinach (October, started indoors) — dates for St. George.
Ready to harvest in May in St. George, if sown in the right month: broad bean (February), peas (March), cabbage (January), beet (March), parsley (March), cilantro (March), arugula (April) and chamomile (March).
Frost-free, highs of 72–82 °F: Salt Lake City, Reno, Grand Junction and Pueblo
In May, on average, these cities have highs of 73 to 78 °F and lows of 47 to 49 °F, 0.9 to 2.2 in of rain on 5 to 8 days; the day lasts 14 h 14 min to 14 h 26 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 | Reno and Pueblo |
| start indoors, plant out in June | Zucchini, cucumber, melon, watermelon, pumpkin, basil, achocha, luffa, okra, peanut | Reno and Pueblo |
| sow direct | Green Beans | Grand Junction and Pueblo |
| sow direct | Sweet Corn, chayote, corn, Florence fennel, kiwano, Napa cabbage | Reno and Pueblo |
| sow direct | Arugula, bok choy, borage | all |
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 Salt Lake City.
Ready to harvest in May in Salt Lake City, 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-free, highs of 61–72 °F: Billings, Fort Collins and Provo
In May, on average, these cities have highs of 69 to 71 °F and lows of 44 to 52 °F, 1.5 to 3.7 in of rain on 7 to 13 days; the day lasts 14 h 24 min to 14 h 55 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 | Radish | Billings |
| 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, luffa, okra, peanut | all |
| sow direct | Green Beans | Provo |
| sow direct | Sweet Corn, arugula, bok choy, borage, chayote, corn, Florence fennel, Napa cabbage | all |
| start indoors, plant out in June or sow direct | Kiwano | all |
| start indoors, plant out in August | Celeriac, celery | Provo |
Compared with April: new — green beans, borage and corn; no longer sown — peas, lettuce, Swiss chard, beet, parsley, cilantro, chamomile, daikon and 3 more.
Not starting in May: lettuce (October, sown direct), peas (October, sown direct) and spinach (October, sown direct) — dates for Fort Collins.
Ready to harvest in May in Fort Collins, if sown in the right month: peas (March), radish (April), arugula (April), dill (April) and mustard greens (April).
Frost possible, highs of 61–72 °F: Denver, Colorado Springs, Cheyenne, Helena and 3 more
In May, on average, these cities have highs of 61 to 71 °F and lows of 38 to 44 °F, 0.9 to 3.4 in of rain on 6 to 15 days; the day lasts 14 h 17 min to 15 h 02 min (on the 15th).
May falls in the frost season: frost-tender crops wait. Average last frost: Denver (May 1), Colorado Springs (May 3), Cheyenne (May 12), Helena (May 19), Carson City (May 1), Missoula (May 18) and Elko (May 6).
| How | What | Where |
|---|---|---|
| sow direct | Peas, beet, chamomile, dill, mustard greens | Cheyenne, Helena, Carson City and 1 more |
| sow direct | Lettuce, Swiss chard | Helena and Missoula |
| sow direct | Radish | Cheyenne, Helena, Carson City and 2 more |
| start indoors, plant out in July | Tomato, bell pepper, eggplant, chili pepper, Florence fennel, moringa | all |
| start indoors, plant out in June | Zucchini, cucumber, melon, watermelon, pumpkin, sweet corn, basil, achocha, bok choy, kiwano, luffa, Napa cabbage, okra, peanut | all |
| sow direct | Parsley, cilantro | Cheyenne, Carson City and Missoula |
| sow direct | Arugula | all |
| sow direct | Kohlrabi | Missoula |
Compared with April: new — zucchini, cucumber, melon, watermelon, pumpkin, sweet corn, parsley, cilantro and 8 more; no longer sown — broad bean, onion, spinach, cabbage, celeriac, celery, chayote, daikon and 4 more.
Not starting in May: green beans (June, sown direct) and spinach (September, started indoors) — dates for Elko.
Ready to harvest in May in Elko, if sown in the right month: radish (April), arugula (April), dill (April) and mustard greens (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.
- Moon planting calendar for May 2027
- What to plant in May: all climates
- Gardening in the United States: guide by region
Other months in the Mountain West
- What to plant in May in the Northeast and Midwest
- What to plant in May in the South
- What to plant in May in Texas
- What to plant in May in Florida
- What to plant in May in California
- What to plant in May in the Pacific Northwest
- What to plant in May in the Southwest
- What to plant in May in Canada
- What to plant in May in the UK
- What to plant in May in Ireland
