What to plant in March in the Mountain West

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

What to sow and plant in March in the Mountain West, by zone: frost possible, highs of 61–72 °F (Pueblo and St. George): broad bean, peas, onion, lettuce, radish and 23 more; frost possible, highs of 50–61 °F (Denver, Salt Lake City and 4 more): broad bean, peas, onion, spinach, lettuce and 12 more; frost possible, highs below 50 °F (Billings, Cheyenne and 5 more): broad bean, spinach, lettuce, Swiss chard, beet and 7 more.

In the Mountain West, March is spring.

Frost possible, highs of 61–72 °F: Pueblo and St. George

In March, on average, these cities have highs of 62 to 65 °F and lows of 32 to 41 °F, 1.0 to 1.3 in of rain on 4 to 6 days; the day lasts 11 h 54 min to 11 h 55 min (on the 15th).

March falls in the frost season: frost-tender crops wait. Average last frost: St. George (March 7).

How	What	Where
sow direct	Broad bean, lettuce, cabbage, Swiss chard	Pueblo
sow direct	Peas, radish, beet, arugula, chamomile, dill, mustard greens	all
plant sets	Onion, shallot	Pueblo
start indoors, plant out in May	Tomato, bell pepper, eggplant, chili pepper, Florence fennel, moringa	Pueblo
start indoors, plant out in April	Zucchini, cucumber, basil, bok choy	St. George
sow direct	Parsley, cilantro	St. George
start indoors, plant out in June	Celeriac, celery, chayote	Pueblo

Compared with February: new — tomato, bell pepper, zucchini, cucumber, eggplant, cilantro, basil, bok choy and 3 more; no longer sown — spinach, cauliflower, kohlrabi and daikon.

Not starting in March: green beans (May, sown direct) and spinach (October, started indoors) — dates for Pueblo.

Ready to harvest in March in Pueblo, if sown in the right month: cabbage (November).

Frost possible, highs of 50–61 °F: Denver, Salt Lake City, Colorado Springs, Reno and 2 more

In March, on average, these cities have highs of 53 to 56 °F and lows of 25 to 33 °F, 1.4 to 3.3 in of rain on 6 to 12 days; the day lasts 11 h 53 min to 11 h 54 min (on the 15th).

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

How	What	Where
sow direct	Broad bean, spinach, cabbage, daikon	Salt Lake City, Reno and Grand Junction
sow direct	Peas, radish	all
plant sets	Onion, shallot	Salt Lake City, Reno and Grand Junction
start indoors, plant out in April or sow direct	Lettuce, Swiss chard, arugula, chamomile	all
start indoors, plant out in April	Beet	all
start indoors, plant out in May	Tomato, bell pepper, eggplant, chili pepper, Florence fennel, moringa	Reno and Fort Collins
start indoors, plant out in April	Kohlrabi	Denver, Salt Lake City, Colorado Springs and 2 more
start indoors, plant out in June	Celeriac, celery, chayote	Denver, Colorado Springs, Reno and 1 more
sow direct	Kale, parsnip, turnip	Salt Lake City and Reno

Compared with February: new — peas, onion, radish, cabbage, tomato, bell pepper, eggplant, daikon and 6 more; no longer sown — cauliflower and parsley.

Not starting in March: zucchini (April, started indoors) and green beans (June, sown direct) — dates for Fort Collins.

Frost possible, highs below 50 °F: Billings, Cheyenne, Helena, Carson City and 3 more

In March, on average, these cities have highs of 41 to 50 °F and lows of 21 to 33 °F, 1.3 to 3.1 in of rain on 8 to 11 days; the day lasts 11 h 51 min to 11 h 54 min (on the 15th).

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

How	What	Where
start indoors, plant out in April or sow direct	Broad bean	Cheyenne, Helena, Carson City and 2 more
sow direct	Peas, radish, cabbage, turnip	Provo
plant sets	Onion	Provo
start indoors, plant out in April or sow direct	Spinach	Cheyenne, Helena, Carson City and 3 more
start indoors, plant out in April or sow direct	Lettuce	all
start indoors, plant out in April	Cauliflower	Cheyenne, Carson City and Missoula
start indoors, plant out in April	Swiss Chard, beet, arugula, chamomile	Billings, Cheyenne, Carson City and 3 more
start indoors, plant out in May	Tomato, bell pepper, eggplant, chili pepper, Florence fennel, moringa	Billings and Provo
start indoors, plant out in May	Parsley	Cheyenne, Helena, Carson City and 1 more
start indoors, plant out in June	Celeriac, celery, chayote	all
start indoors, plant out in April	Kohlrabi	all
start indoors, plant out in April	Kale	Missoula

Compared with February: new — peas, onion, radish, cauliflower, Swiss chard, beet, tomato, bell pepper and 8 more; no longer sown — broccoli and Brussels sprouts.

Not starting in March: zucchini (May, started indoors) and green beans (June, sown direct) — dates for Carson City.

How we work it out

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