Warm-Season Vegetable

When to Plant Tomatoes in Idaho

America's favorite garden vegetable (technically a fruit). Nothing beats a sun-warmed tomato straight off the vine.

The Short Answer

In Idaho, tomatoes planting dates vary by region. In Northern Idaho, your average last frost is around May 5 - May 25, while Eastern Idaho sees its last frost around May 20 - Jun 10. Since tomatoes are frost-sensitive, start seeds indoors 6 weeks before your last frost, then transplant outside 2 weeks after frost danger has passed. Volcanic ash soils in south — excellent for gardening. Rocky soils in mountains. Alkaline in many areas.

Idaho Frost Dates

Your planting dates depend on which part of Idaho you're in. Here are the frost date ranges by region:

Region Zones Last Frost (Spring) First Frost (Fall)
Northern Idaho 5a, 5b, 6a May 5 - May 25 Sep 15 - Oct 5
Boise Area 6b, 7a Apr 20 - May 5 Oct 5 - Oct 20
Eastern Idaho 3b, 4a, 4b, 5a May 20 - Jun 10 Sep 1 - Sep 20

Tomatoes Planting Schedule for Idaho

Northern Idaho (Zones 5a, 5b, 6a)

Average last frost: May 5 - May 25 · Average first frost: Sep 15 - Oct 5

Start Seeds Indoors
6 wks before frost
Transplant Outside
2 wks after frost
Direct Sow
2 wks after frost

Boise Area (Zones 6b, 7a)

Average last frost: Apr 20 - May 5 · Average first frost: Oct 5 - Oct 20

Start Seeds Indoors
6 wks before frost
Transplant Outside
2 wks after frost
Direct Sow
2 wks after frost

Eastern Idaho (Zones 3b, 4a, 4b, 5a)

Average last frost: May 20 - Jun 10 · Average first frost: Sep 1 - Sep 20

Start Seeds Indoors
6 wks before frost
Transplant Outside
2 wks after frost
Direct Sow
2 wks after frost

Growing Tomatoes in Idaho

Tomatoes in Idaho's Climate

In cold climates with 120-160 frost-free days, tomatoes demand an aggressive indoor start 6-8 weeks before your last frost. Choose short-season varieties that mature in 55-65 days — Stupice, Sub Arctic Plenty, and Glacier are bred for regions exactly like yours. Black plastic mulch can raise soil temperature by 10-15°F, and floating row cover over transplants during cool June nights adds critical warmth. Your goal is getting ripe tomatoes before September frost — every warm day counts.

Soil Considerations for Idaho

Volcanic ash soils in south — excellent for gardening. Rocky soils in mountains. Alkaline in many areas. Make sure soil has warmed to at least 60°F before planting tomatoes outside.

Idaho Climate & Growing Season

Arid climate. Low humidity. Hot days and cool nights. Irrigation essential. Short season at higher elevations. Tomatoes cannot tolerate any frost, so wait until all frost danger has passed before transplanting outside. Watch local forecasts carefully in spring.

Growing season length varies across Idaho: Northern Idaho (5a, 5b, 6a) has a last frost around May 5 - May 25, while Eastern Idaho (3b, 4a, 4b, 5a) sees frost end around May 20 - Jun 10. This difference matters for tomatoes — transplant timing shifts by several weeks across the state.

Growing Tips

Pinch off suckers for indeterminate varieties. Stake or cage for best results. Water at the base, not overhead, to prevent blight.

Companion Planting

Plant tomatoes alongside these companions for better growth:

Basil Carrots Peppers Marigolds

Keep tomatoes away from:

Brassicas Fennel Dill

The Bottom Line

Tomatoes can be grown successfully across Idaho, but your exact planting dates depend on which region you're in. Northern Idaho gardeners should plan around a May 5 - May 25 last frost, while those in Eastern Idaho can typically plant later. For exact dates based on your zip code, use our free planting date finder.

Related Guides

Tomatoes Growing Guide National planting guide with all states Idaho Planting Calendar All plants for Idaho Tomatoes in Alabama Alabama planting dates Tomatoes in Alaska Alaska planting dates Tomatoes in Arizona Arizona planting dates Tomatoes in Arkansas Arkansas planting dates
Note: All dates are based on NOAA 30-year Climate Normals and represent historical averages, not predictions for any specific year. Always check your local weather forecast before planting frost-sensitive crops. Learn about our data sources.

Last reviewed: March 29, 2026

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