Last and first frost dates in Boise

When is the last frost in Boise?

The last frost in Boise usually comes around 15 April: 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 25 March, while corn waits until 22 April. The first autumn frost follows around 27 October, about 195 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.

What planting zone is Boise?

The official USDA map (2023, 1991–2020 data) puts the centre of Boise (ZIP 83724) in zone 7a. Zone 7a stands for an average coldest night of 0 to 5 °F (-17.8 to -15 °C), so perennials hardy to zone 7a or a colder zone should come through a typical winter here.

Check the official USDA map for Boise: USDA Plant Hardiness Zone Map.

When the soil warms up in Boise

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 11 days before the last spring frost and 15 °C 12 days after it.

Frost dates near Boise

Of the nearest cities on our list, the last spring frost ends earliest in Spokane (21 April) and latest in Helena (19 May).

Seeds, seedlings and markets in Boise

Within 15 km of Boise OpenStreetMap lists 4 garden centres, 2 farm-supply shops and 1 plant nursery (collected 20 October 2026). The nearest garden centre to the city centre is North End Organic Nursery, 4 km away.

• North End Organic Nursery — garden centre
  West Chinden Boulevard 3777, 83714 Garden City · 4 km
• Zamzows — farm supply
  West State Street 6208, 83703 Boise · 8 km
• Madeline George Garden Design & Nursery — plant nursery
  West Hill Road Parkway 10550, 83714 Boise · 13 km · madelinegeorge.com
• Zamzows — garden centre
  South Federal Way 3691, 83716 Boise · Mon–Fri 09:00–19:00; Sun 22:00–17:00; Sat 09:00–18:00 · 5 km
• Zamzows — farm supply
  East Overland Road 3650, 83642 Meridian · 12 km
• Zamzows — garden centre
  West Fairview Avenue 6313, 83704 Boise · 5 km

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

Places: © OpenStreetMap contributors, ODbL.

Weather in Boise by month

Average weather in Boise over 2016–2025: the warmest month is July. Months that average 20 °C or more by day: May–September (23–35.1 °C). Months that average 30 °C or more by day: July (35.1 °C) and August (33.7 °C). Nights average below 0 °C in January (-3.7 °C), February (-2.1 °C) and December (-3 °C). About 373 mm of rain falls in a year, on 79 days; December is the wettest month (54 mm) and July the driest (3 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).