Last and first frost dates in Idaho Falls

When is the last frost in Idaho Falls?

The last frost in Idaho Falls usually comes around 11 May: that is the median of 2016–2025, so in about half of those years the last night at or below 0 °C came later. Hardy crops start before it and frost-tender ones only after it: in the table below arugula can go into open ground from 20 April, while corn waits until 18 May. The first autumn frost follows around 14 October, about 156 days later: harvest or cover frost-tender crops before then.

When to sow and plant

Planting out: a week after the last frost once the soil is warm enough for the crop; frost-hardy crops three weeks before it; an unheated greenhouse three weeks earlier. Seedlings are sown so they are ready on that day. Each window starts on the Greenly calendar date and ends on the last day that still leaves the crop’s days to harvest (from its card) before the average first autumn frost, plus six weeks of picking for crops harvested over weeks (tomatoes, peppers, aubergines, cucumbers, courgettes, pumpkins, watermelons, beans) — our rule; earlier in the window is safer.

When the soil warms up in Idaho Falls

The day the top 7 cm of soil first averages each temperature over a week, median of 2016–2025 (ERA5 via Open-Meteo). The soil reaches 10 °C 15 days before the last spring frost and 15 °C 2 days after it.

Frost dates near Idaho Falls

Of the nearest cities on our list, the last spring frost ends earliest in Provo (6 April) and latest in Helena (19 May).

Seeds, seedlings and markets in Idaho Falls

Within 15 km of Idaho Falls OpenStreetMap lists 4 garden centres, 3 farm-supply shops, 2 plant nurseries, 2 markets and 1 farm shop (collected 28 October 2026). The nearest garden centre to the city centre is Town and Country Gardens, 7 km away.

• Town and Country Gardens — garden centre
  South Yellowstone Highway 5800, 83402 Idaho Falls · 7 km · tcgardens.com
• Siems Enterprises LLC — farm supply
  Mon, Thu, Fri 08:00–17:00; Tue 08:00–16:15; Wed 08:00–15:00; Sat 09:00–12:00 · 15 km
• Itty Bitty Farms — farm shop
  East Lincoln Road 5229, 83401-5769 Idaho Falls · 8 km · ittybittyfarmstore.com
• R & D Wholesale Nursery — garden centre
  West Heritage Circle 2312, 83402 Idaho Falls · 8 km

• Where to buy seeds and seedlings in Idaho Falls
• Selling your own harvest in the United States

Places: © OpenStreetMap contributors, ODbL.

Weather in Idaho Falls by month

Average weather in Idaho Falls over 2016–2025: the warmest month is July. Months that average 20 °C or more by day: May–September (20.6–32.9 °C). Months that average 30 °C or more by day: July (32.9 °C) and August (30.9 °C). Nights average below 0 °C in November–March (-9.4–-2.8 °C). About 349 mm of rain falls in a year, on 85 days; May is the wettest month (43 mm) and July the driest (5 mm).

Average of the daily highs and lows, rain per month and days with at least 1 mm (ERA5 via Open-Meteo, the same grid cell as the frost dates).

Planted in autumn

From a month before the first autumn frost, so the roots grow before winter, to the late-planting limit on each crop’s page (about two weeks before the ground freezes, by ten years of weather).