What to plant in April in the Mountain West

Worked out for 15 cities from their own weather and frost dates, by zone.

What to sow and plant in April in the Mountain West, by zone: frost-free, highs of 72–82 °F (St. George): green beans, arugula, bok choy and borage; frost possible, highs of 61–72 °F (Denver, Salt Lake City and 5 more): peas, lettuce, radish, Swiss chard, beet and 19 more; frost possible, highs of 50–61 °F (Billings, Cheyenne and 4 more): broad bean, peas, onion, spinach, lettuce and 19 more; frost possible, highs below 50 °F (Helena): lettuce, Swiss chard, beet, tomato, bell pepper and 10 more.

In the Mountain West, April is spring.

Frost-free, highs of 72–82 °F: St. George

In April, on average, St. George has highs of 77 °F and lows of 49 °F, 0.5 in of rain on 2 days; the day lasts 13 h 08 min (on the 15th). A dry month: whatever is sown needs watering.

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

How	What	Where
sow direct	Green Beans, arugula, bok choy, borage	St. George

Compared with March: new — green beans and borage; no longer sown — peas, radish, beet, zucchini, cucumber, parsley, cilantro, basil and 3 more.

Not starting in April: tomato (no month outdoors by these rules), bell pepper (no month outdoors by these rules), zucchini (September, sown direct), lettuce (October, started indoors), peas (October, sown direct) and spinach (October, started indoors) — dates for St. George.

Ready to harvest in April in St. George, if sown in the right month: broad bean (January), peas (February), spinach (February), lettuce (February), radish (March), cabbage (December), Swiss chard (February) and beet (February).

Frost dates in St. George

Frost possible, highs of 61–72 °F: Denver, Salt Lake City, Colorado Springs, Reno and 3 more

In April, on average, these cities have highs of 63 to 70 °F and lows of 33 to 40 °F, 1.0 to 2.8 in of rain on 5 to 10 days; the day lasts 13 h 10 min to 13 h 17 min (on the 15th).

April falls in the frost season: frost-tender crops wait. Average last frost: Salt Lake City (April 24), Reno (April 16), Fort Collins (April 25), Grand Junction (April 18) and Pueblo (April 21).

How	What	Where
sow direct	Peas, beet, arugula, chamomile, dill, mustard greens	all
sow direct	Lettuce, Swiss chard	Denver, Salt Lake City, Colorado Springs and 2 more
sow direct	Radish	Denver, Salt Lake City, Colorado Springs and 3 more
start indoors, plant out in June	Tomato, bell pepper, eggplant, chili pepper, Florence fennel, moringa	Denver, Colorado Springs, Reno and 2 more
start indoors, plant out in May	Zucchini, cucumber, basil, bok choy	Salt Lake City, Reno, Fort Collins and 2 more
start indoors, plant out in May	Melon, watermelon, pumpkin, sweet corn, achocha, kiwano, luffa, Napa cabbage, okra, peanut	Reno, Fort Collins and Pueblo
sow direct	Parsley, cilantro	Salt Lake City, Reno, Grand Junction and 1 more
start indoors, plant out in July	Celeriac, celery, chayote	Denver, Colorado Springs, Reno and 2 more
sow direct	Kohlrabi	Salt Lake City and Reno

Compared with March: new — zucchini, cucumber, melon, watermelon, pumpkin, sweet corn, parsley, cilantro and 8 more; no longer sown — broad bean, onion, spinach, cabbage, daikon, kale, parsnip, shallot and 1 more.

Not starting in April: green beans (June, sown direct) and spinach (October, sown direct) — dates for Colorado Springs.

Ready to harvest in April in Colorado Springs, if sown in the right month: radish (March).

Frost possible, highs of 50–61 °F: Billings, Cheyenne, Carson City, Missoula and 2 more

In April, on average, these cities have highs of 53 to 60 °F and lows of 30 to 43 °F, 1.3 to 2.6 in of rain on 6 to 11 days; the day lasts 13 h 13 min to 13 h 34 min (on the 15th).

April falls in the frost season: frost-tender crops wait. Average last frost: Billings (April 25) and Provo (April 6).

How	What	Where
sow direct	Broad bean, cabbage	Cheyenne, Carson City and Missoula
sow direct	Peas, lettuce, radish, Swiss chard, arugula, chamomile	all
plant sets	Onion, shallot	Cheyenne, Carson City and Missoula
sow direct	Spinach	Cheyenne, Carson City, Missoula and 1 more
sow direct or start indoors, plant out in May	Beet	all
start indoors, plant out in June	Tomato, bell pepper, eggplant, chili pepper, Florence fennel, moringa	all
start indoors, plant out in May	Zucchini, cucumber, melon, watermelon, pumpkin, sweet corn, basil, achocha, bok choy, kiwano, luffa, Napa cabbage, okra, peanut	Billings and Provo
sow direct	Parsley, cilantro	Provo
start indoors, plant out in July	Celeriac, celery, chayote	all
sow direct	Daikon	Billings, Cheyenne, Carson City and 2 more
sow direct	Dill, mustard greens	Billings, Carson City, Elko and 1 more
start indoors, plant out in May or sow direct	Kohlrabi	Missoula and Provo
sow direct	Turnip	Cheyenne and Missoula
sow direct	Kale, parsnip	Missoula

Compared with March: new — zucchini, cucumber, melon, watermelon, pumpkin, sweet corn, cilantro, basil and 12 more; no longer sown — cauliflower.

Not starting in April: green beans (June, sown direct) — dates for Elko.

Frost possible, highs below 50 °F: Helena

In April, on average, Helena has highs of 50 °F and lows of 27 °F, 2.1 in of rain on 10 days; the day lasts 13 h 33 min (on the 15th).

April falls in the frost season: frost-tender crops wait.

How	What	Where
start indoors, plant out in May	Lettuce, Swiss chard, beet, arugula, chamomile, kohlrabi	Helena
start indoors, plant out in June	Tomato, bell pepper, eggplant, chili pepper, Florence fennel, moringa	Helena
start indoors, plant out in July	Celeriac, celery, chayote	Helena

Compared with March: new — Swiss chard, beet, tomato, bell pepper, eggplant, arugula, chamomile, chili pepper and 2 more; no longer sown — broad bean, spinach and parsley.

Not starting in April: zucchini (May, started indoors), green beans (July, sown direct), peas (May, sown direct) and spinach (September, started indoors) — dates for Helena.

Frost dates in Helena

How we work it out

For each city we use its average weather in April 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 April 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.