What to plant in October in the Mountain West

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

What to sow and plant in October in the Mountain West, by zone: frost-free, highs of 72–82 °F (St. George): garlic, broad bean, peas, onion, spinach and 18 more; frost possible, highs of 72–82 °F (Pueblo): garlic, broad bean, peas, onion, spinach and 18 more; frost possible, highs of 61–72 °F (Denver, Salt Lake City and 8 more): garlic, broad bean, peas, onion, spinach and 15 more; frost-free, highs of 61–72 °F (Provo): garlic, peas, spinach, lettuce, radish and 4 more; frost possible, highs of 50–61 °F (Helena and Missoula): garlic, peas, spinach, radish, arugula and 2 more.

In the Mountain West, October is fall.

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

In October, on average, St. George has highs of 78 °F and lows of 51 °F, 0.4 in of rain on 2 days; the day lasts 11 h 17 min (on the 15th). A dry month: whatever is sown needs watering.

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

How	What	Where
plant cloves	Garlic	St. George
sow direct	Broad bean, peas, cabbage, beet, parsley, cilantro, arugula, chamomile, chickpea, dill, mustard greens	St. George
plant sets	Onion, shallot	St. George
start indoors, plant out in November	Spinach, lettuce, cauliflower, Swiss chard, chicory, kale, kohlrabi	St. George
start indoors, plant out in December	Broccoli, Brussels sprouts	St. George

Compared with September: new — garlic, broad bean, peas, onion, spinach, lettuce, cabbage, broccoli and 15 more; no longer sown — zucchini, green beans, basil, bok choy and borage.

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

Frost dates in St. George

Frost possible, highs of 72–82 °F: Pueblo

In October, on average, Pueblo has highs of 72 °F and lows of 43 °F, 0.6 in of rain on 3 days; the day lasts 11 h 15 min (on the 15th). A dry month: whatever is sown needs watering.

October falls in the frost season: frost-tender crops wait. Average first frost: Pueblo (October 28).

How	What	Where
plant cloves	Garlic	Pueblo
sow direct	Broad bean, peas, lettuce, carrot, cabbage, broccoli, Swiss chard, beet, parsley, cilantro, arugula, chamomile, chickpea, dill, kale, kohlrabi, mustard greens, parsnip	Pueblo
plant sets	Onion, shallot	Pueblo
start indoors, plant out in November	Spinach	Pueblo
plant bulbs	Crocus, daffodil, hyacinth, tulip	Pueblo

Compared with September: new — broad bean, peas, onion, spinach, lettuce, carrot, cabbage, broccoli and 13 more.

Not starting in October: tomato (March, started indoors), bell pepper (March, started indoors), zucchini (April, started indoors) and green beans (May, sown direct) — dates for Pueblo.

Ready to harvest in October in Pueblo, if sown in the right month: zucchini (August), green beans (August), watermelon (July), pumpkin (June), sweet corn (July), basil (August), bok choy (August) and borage (August).

Frost dates in Pueblo

Frost possible, highs of 61–72 °F: Denver, Salt Lake City, Colorado Springs, Reno and 6 more

In October, on average, these cities have highs of 61 to 69 °F and lows of 38 to 45 °F, 0.8 to 2.1 in of rain on 4 to 7 days; the day lasts 11 h 00 min to 11 h 14 min (on the 15th).

October falls in the frost season: frost-tender crops wait. Average first frost: Denver (October 15), Salt Lake City (October 26), Colorado Springs (October 15), Reno (October 28), Billings (October 14), Cheyenne (October 13), Carson City (October 22), Fort Collins (October 21), Grand Junction (October 27) and Elko (October 13).

How	What	Where
plant cloves	Garlic	all
sow direct	Broad bean, cabbage, broccoli	Denver, Salt Lake City, Colorado Springs and 5 more
sow direct	Peas, lettuce, radish, arugula	all
plant sets	Onion	Denver, Salt Lake City, Colorado Springs and 5 more
sow direct or start indoors, plant out in November	Spinach	all
sow direct	Swiss Chard, beet, parsley, cilantro, chamomile, daikon, dill, kohlrabi, mustard greens	Denver, Salt Lake City, Colorado Springs and 4 more
sow direct	Turnip	Billings, Cheyenne, Carson City and 1 more
plant bulbs	Crocus, daffodil, hyacinth, tulip	all

Compared with September: new — radish, broccoli, daikon and turnip; no longer sown — chickpea and shallot.

Not starting in October: tomato (no month outdoors by these rules), bell pepper (no month outdoors by these rules), zucchini (April, started indoors) and green beans (August, sown direct) — dates for Salt Lake City.

Ready to harvest in October in Salt Lake City, if sown in the right month: zucchini (August), green beans (August), basil (August), bok choy (August) and borage (August).

Frost-free, highs of 61–72 °F: Provo

In October, on average, Provo has highs of 64 °F and lows of 48 °F, 1.4 in of rain on 6 days; the day lasts 11 h 11 min (on the 15th).

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

How	What	Where
plant cloves	Garlic	Provo
sow direct	Peas, spinach, lettuce, radish, arugula, kohlrabi, turnip	Provo
plant bulbs	Crocus, daffodil, hyacinth, tulip	Provo

Compared with September: new — garlic, peas, spinach, lettuce, radish, arugula, kohlrabi, turnip and 4 more.

Not starting in October: tomato (March, started indoors), bell pepper (March, started indoors), zucchini (April, started indoors) and green beans (May, sown direct) — dates for Provo.

Ready to harvest in October in Provo, if sown in the right month: zucchini (August), green beans (August), watermelon (July), pumpkin (June), sweet corn (July), basil (August), bok choy (August) and borage (August).

Frost dates in Provo

Frost possible, highs of 50–61 °F: Helena and Missoula

In October, on average, these cities have highs of 54 to 55 °F and lows of 33 to 35 °F, 1.8 to 2.3 in of rain on 9 to 11 days; the day lasts 10 h 57 min to 10 h 58 min (on the 15th).

October falls in the frost season: frost-tender crops wait. Average first frost: Helena (October 3) and Missoula (October 6).

How	What	Where
plant cloves	Garlic	all
sow direct	Peas, spinach, radish, arugula, turnip	all
plant bulbs	Crocus, daffodil, hyacinth, tulip	all

Compared with September: new — radish and turnip; no longer sown — broad bean, onion, lettuce, cabbage, broccoli, Swiss chard, beet, parsley and 5 more.

Not starting in October: tomato (April, started indoors), bell pepper (April, started indoors), zucchini (May, started indoors), green beans (July, sown direct) and lettuce (March, started indoors) — dates for Helena.

Ready to harvest in October in Helena, if sown in the right month: peas (August), beet (August), watermelon (July), sweet corn (July), parsley (August), cilantro (August), arugula (September) and chamomile (August).

How we work it out

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