Idaho vegetable planting calendar 2027: frost dates and when to plant
In Idaho, the average last spring frost is May 17 in Boise (NOAA 1991-2020 normals). Below are planting dates for Boise for 27 common vegetables and herbs, worked out the way the Rowtime app does it: NOAA's average frost dates for the nearest weather station, with the planting rules of state extension guides. Dates are for the 2027 season.
Rowtime: Garden Planner works these dates out for your own ZIP code in Idaho, shows where each one comes from, and recalculates when a planting slips. Get Rowtime on the App Store.
Dates are estimates. Check your local extension office before you plant, and use your own frost records if you have them. Dates shift by a week or more within a state, so pick the city closest to your conditions.
Boise
When to plant tomatoes in Boise?
In Boise, Idaho, the average last spring frost is May 17 and the average first fall frost is October 12 (NOAA 1991-2020 normals, BOISE 7 N station, 9.3 km from ZIP 83702). For tomatoes, start seeds indoors April 21 to June 27 and plant out seedlings June 7 to July 14, following University of Maryland Extension (Home & Garden Information Center) and Utah State University Extension. Dates are for the 2027 season; sources last checked October 24, 2026.
Frost dates for Boise (83702)
- Last spring frost: May 17 on average, Jun 10 for a 10% risk of a later frost.
- First fall frost: Oct 12 on average, Sep 27 for a 10% risk of an earlier frost.
- USDA hardiness zone 7a (PRISM 2023 listing).
| Crop | When |
|---|---|
| Beet | Sow outdoors: May 10 to Aug 13 Sow outdoors for fall: Aug 2 to Aug 30 |
| Broccoli | Start seeds indoors: Mar 31 to May 7 Plant out seedlings: Apr 29 to May 13 Plant out seedlings for fall: Aug 2 to Aug 30 |
| Cabbage | Start seeds indoors: Mar 24 to Apr 20 Plant out seedlings: Apr 29 to May 13 Plant out seedlings for fall: Aug 2 to Aug 30 |
| Carrot | Sow outdoors: May 10 to Jul 24 |
| Cauliflower | Start seeds indoors: Apr 7 to May 7 Plant out seedlings: May 10 to Jul 14 Plant out seedlings for fall: Jun 12 to Jul 12 |
| Cucumber | Sow outdoors: May 24 to Aug 3 |
| Eggplant | Start seeds indoors: May 8 to Jun 6 Plant out seedlings: Jun 7 to Jul 14 |
| Green onion | Plant onion sets: Apr 29 to May 13 Plant out seedlings for fall: Aug 2 to Aug 30 |
| Kale | Sow outdoors: Apr 29 to May 13 Sow outdoors for fall: Aug 2 to Aug 30 |
| Lettuce | Sow outdoors: May 10 to Jul 24 Sow outdoors for fall: Aug 2 to Aug 30 |
| Melon and watermelon | Sow outdoors: Jun 7 to Jul 4 |
| Okra | Plant out seedlings: Jun 24 to Aug 8 |
| Onion | Plant onion sets: Apr 29 to May 13 |
| Pea | Sow outdoors: Apr 29 to May 13 |
| Pepper | Start seeds indoors: Apr 21 to May 21 Plant out seedlings: Jun 7 to Jul 14 |
| Potato | Plant seed potatoes: May 10 to Jul 4 |
| Snap bean | Sow outdoors: May 24 to Aug 13 |
| Spinach | Sow outdoors: Apr 29 to May 13 Sow outdoors for fall: Aug 2 to Aug 30 |
| Summer squash | Sow outdoors: May 24 to Aug 13 |
| Sweet corn | Sow outdoors: May 24 to Jul 14 |
| Sweet potato | Sprout slips indoors: May 22 to Jun 20 Plant out slips: season too short |
| Tomato | Start seeds indoors: Apr 21 to Jun 27 Plant out seedlings: Jun 7 to Jul 14 |
| Winter squash and pumpkin | Sow outdoors: Jun 7 to Jul 4 |
| Basil | Plant outdoors: Jun 20 to Sep 19 |
| Cilantro | Sow outdoors: Mar 23 to May 20 Sow outdoors for fall: Aug 20 to Sep 3 |
| Dill | Sow outdoors: May 5 to May 20 Sow outdoors for fall: Jul 5 to Aug 19 |
| Parsley | Sow outdoors: May 10 to Jul 14 Plant outdoors for fall: Jul 5 to Sep 3 |
Sources
Planting rules, in the order Rowtime tries them here:
- Utah State University Extension, Suggested Vegetable Planting Dates for Utah. Checked October 20, 2026.
- Purdue University Extension, Indiana Vegetable Planting Calendar (HO-186-W). Checked October 20, 2026.
- University of Maryland Extension (Home & Garden Information Center), Vegetable Planting Calendar for Central Maryland. Checked October 24, 2026.
- NC State Extension, Central North Carolina Planting Calendar for Annual Vegetables, Fruits, and Herbs (AG-756-01). Checked October 21, 2026.
Frost dates, locations and zones:
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991-2020 annual/seasonal (freeze probabilities).
- U.S. Census Bureau, 2025 Gazetteer Files: ZIP Code Tabulation Areas.
- PRISM Group, Oregon State University / USDA ARS, 2023 USDA Plant Hardiness Zone Map ZIP code listings. PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed 20 Oct 2026.
How the dates are worked out: a guide's rule such as "two weeks after the last frost" is applied to the station's NOAA date. Purdue's dates are 10% dates, so they are counted from the station's 10% date. When a guide gives no last date, the window closes early enough for the crop's longest days to harvest before the first fall frost. When a guide gives no first date for a fall planting, no fall window is shown. "Season too short" means the guide's window would close before it opens at this station's frost dates.
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