GreenlyWhat to plant in June in the Mountain West
Worked out for 15 cities from their own weather and frost dates, by zone.
What to sow and plant in June in the Mountain West, by zone: frost-free, highs above 82 °F (Denver, Salt Lake City and 7 more): zucchini, green beans, cucumber, melon, watermelon and 16 more; frost-free, highs of 72–82 °F (Billings, Cheyenne and 3 more): zucchini, green beans, cucumber, melon, watermelon and 16 more; frost-free, highs of 61–72 °F (Helena): cabbage, zucchini, cucumber, melon, watermelon and 17 more.
In the Mountain West, June is summer.
Frost-free, highs above 82 °F: Denver, Salt Lake City, Colorado Springs, Reno and 5 more
In June, on average, these cities have highs of 83 to 98 °F and lows of 54 to 70 °F, 0.1 to 1.7 in of rain on 0 to 8 days; the day lasts 14 h 42 min to 15 h 05 min (on the 15th).
No frost in June 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 | Tomato, bell pepper, eggplant, chili pepper | Provo |
| sow direct | Zucchini, green beans, watermelon, pumpkin, sweet corn, basil, bok choy, borage, chayote, corn, Florence fennel, kiwano, luffa, moringa, Napa cabbage, okra, peanut, soybean | Denver, Colorado Springs, Reno and 3 more |
| start indoors, plant out in July | Cucumber, melon, achocha | Denver, Colorado Springs, Reno and 3 more |
Compared with May: new — soybean; no longer sown — arugula, celeriac and celery.
Not starting in June: lettuce (October, sown direct), peas (October, sown direct) and spinach (October, sown direct) — dates for Provo.
Ready to harvest in June in Provo, if sown in the right month: broad bean (March), peas (April), lettuce (April), Swiss chard (April), beet (April), parsley (April), cilantro (April) and arugula (May).
Frost-free, highs of 72–82 °F: Billings, Cheyenne, Carson City, Missoula and 1 more
In June, on average, these cities have highs of 72 to 81 °F and lows of 47 to 55 °F, 0.3 to 2.5 in of rain on 2 to 10 days; the day lasts 14 h 54 min to 15 h 51 min (on the 15th).
No frost in June in 10 years of data: frost-tender crops can go in too, if it is warm enough for them.
| How | What | Where |
|---|---|---|
| sow direct or start indoors, plant out in July | Zucchini, watermelon, pumpkin, basil, luffa, okra, peanut | all |
| sow direct | Green Beans, soybean | Billings, Cheyenne, Carson City and 1 more |
| start indoors, plant out in July | Cucumber, melon, achocha | all |
| sow direct | Sweet Corn, bok choy, borage, chayote, corn, Florence fennel, kiwano, Napa cabbage | all |
| sow direct | Arugula | Cheyenne, Carson City and Missoula |
Compared with May: new — green beans and soybean; no longer sown — peas, lettuce, radish, Swiss chard, beet, tomato, bell pepper, eggplant and 8 more.
Not starting in June: tomato (April, started indoors), bell pepper (April, started indoors), lettuce (September, started indoors), peas (September, sown direct) and spinach (September, started indoors) — dates for Cheyenne.
Ready to harvest in June in Cheyenne, if sown in the right month: peas (April), spinach (April), lettuce (April), radish (May), Swiss chard (April), arugula (May), chamomile (April) and daikon (April).
Frost-free, highs of 61–72 °F: Helena
In June, on average, Helena has highs of 71 °F and lows of 46 °F, 2.7 in of rain on 11 days; the day lasts 15 h 49 min (on the 15th).
No frost in June 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 | Cabbage, parsley, Brussels sprouts | Helena |
| start indoors, plant out in July | Zucchini, cucumber, melon, watermelon, pumpkin, basil, achocha, kiwano, luffa, okra, peanut | Helena |
| sow direct | Sweet Corn, arugula, bok choy, borage, chayote, corn, Florence fennel, Napa cabbage | Helena |
Compared with May: new — cabbage, parsley, borage, Brussels sprouts, chayote and corn; no longer sown — peas, lettuce, radish, Swiss chard, beet, tomato, bell pepper, eggplant and 5 more.
Not starting in June: tomato (April, started indoors), bell pepper (April, started indoors), green beans (July, sown direct), lettuce (August, started indoors), peas (August, sown direct) and spinach (September, started indoors) — dates for Helena.
Ready to harvest in June in Helena, if sown in the right month: radish (May), arugula (May), dill (May) and mustard greens (May).
How we work it out
For each city we use its average weather in June 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 June 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.
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