Root Vegetable

When to Plant Radishes in Idaho

The fastest vegetable in the garden — some varieties are ready in just 25 days. Perfect for impatient gardeners and kids.

The Short Answer

In Idaho, soil conditions are an important factor for radishes. Volcanic ash soils in south — excellent for gardening. Rocky soils in mountains. Alkaline in many areas. Direct sow 4 weeks before your last frost date. Radishes can also be planted in fall, 6 weeks before your first frost.

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

Radishes Planting Schedule for Idaho

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

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

Direct Sow
4 wks before frost
Fall Planting
6 wks before first frost

Boise Area (Zones 6b, 7a)

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

Direct Sow
4 wks before frost
Fall Planting
6 wks before first frost

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

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

Direct Sow
4 wks before frost
Fall Planting
6 wks before first frost

Growing Radishes in Idaho

Radishes in Idaho's Climate

Radishes are perfect for cold-climate gardens — they're the fastest crop from seed to harvest (as few as 22 days) and tolerate frost. Direct sow as soon as soil thaws. Your cool, long spring means radishes grow for weeks without the bolting pressure that ends the season rapidly in warm zones. Fall radishes from an August sowing are equally productive.

Soil Considerations for Idaho

Volcanic ash soils in south — excellent for gardening. Rocky soils in mountains. Alkaline in many areas. Loose, well-drained soil is especially important for radishes since the edible portion grows underground. If your soil is heavy clay, consider raised beds.

Idaho Climate & Growing Season

Arid climate. Low humidity. Hot days and cool nights. Irrigation essential. Short season at higher elevations. Radishes can handle frost well, which is an advantage in Idaho's climate. You can push planting dates earlier in spring and extend into fall.

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 radishes — but radishes handle frost well, so the timing difference is less critical.

Growing Tips

Don't let them stay in the ground too long — they get pithy and hot. Succession plant every 2 weeks for continuous harvest.

Companion Planting

Plant radishes alongside these companions for better growth:

Peas Lettuce Carrots Spinach

The Bottom Line

Radishes 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

Radishes Growing Guide National planting guide with all states Idaho Planting Calendar All plants for Idaho Radishes in Alabama Alabama planting dates Radishes in Alaska Alaska planting dates Radishes in Arizona Arizona planting dates Radishes 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

Ready to Start Planting?

Enter your zip code and pick your plant. We'll tell you exactly when to plant, start seeds, and harvest — based on where you live.

Find Your Planting Dates