When to Plant Radishes in Duluth, MN
Published: April 24, 2026
Radish Planting Dates for Duluth, MN
| Start seeds indoors | Year-round |
| Last frost (average) | May 7 |
| Direct sow outdoors | April 2–12 |
| Minimum soil temperature | 40°F |
| Expect first harvest | April 24 – May 2 |
| Fall crop planting | August 27–September 6 |
| Fall crop harvest | September 18 |
| First fall frost (average) | October 1 |
⚠ Direct sow radishes 4–6 weeks before last frost — one of the fastest crops in the garden. Ready in as little as 22 days. Succession plant every 2 weeks for continuous harvest.
Best Radish Varieties for Duluth, MN
Consult a Duluth-area nursery or your state extension office for radish varieties proven in Zone 4b.
Growing Radishes in Duluth
Duluth sits in Zone 4b, with an average last frost of May 7 and first fall frost around October 1 — giving a 147-day frost-free growing season. Cool-season crops like radish benefit from Duluth's cooler spring and fall windows, when temperatures stay in the 55–75°F sweet spot that produces the best flavor and least bolting.
Duluth's cooler summers are close to ideal for radish. The same conditions that limit tomato and pepper yields benefit cool-season crops — slower bolting, sweeter flavor, and longer harvest windows. The fall radish crop in Duluth is often more productive than the spring crop.
Duluth's clay-loam soils are productive but benefit from annual compost amendment — 2 to 3 inches worked in before planting improves drainage and nutrient availability for radish. Consistent watering (1 inches per week) paired with organic mulch maintains the even moisture that clay-loam holds well. Avoid working wet soil in spring, which causes severe compaction in clay-loam blends.
Radish Calendar for Duluth
| Month | Task |
|---|---|
| Year | Start seeds indoors under grow lights |
| May | Last frost — soil warming, prepare bed |
| April | Direct sow seeds into warm soil |
| August | Start fall crop — transplants or direct sow |
| October | First fall frost — harvest remaining, end of outdoor season |
Radish Tips for Duluth Gardeners
- •Thin to 2-inch spacing when seedlings are an inch tall — crowded radishes produce small woody roots.
- •Succession plant every 10–14 days from early spring through late spring for continuous harvest.
- •Fall plantings in Duluth often out-produce spring plantings — cooler temperatures slow bolting and concentrate flavor. Light frost can actually improve the taste of radish.
Common Radish Pests in Duluth
- •Flea Beetle — peaks July in Zone 4b (active June–August); tiny black beetles that riddle leaves with holes; row covers protect seedlings.
- •Cabbage Root Maggot — peaks July in Zone 4b (active June–August); monitor closely during peak season and treat early.
- •Aphid — peaks July in Zone 4b (active June–August); monitor closely during peak season and treat early.
Check plants every 2–3 days during peak season — early intervention prevents most infestations from becoming serious.
What to Plant with Radishes in Duluth
In Duluth's cold climate, Lettuce and Carrot are the most beneficial plants to grow alongside radish. Lettuce improves nearby plant health and pest resistance. Keep radish away from Hyssop — it competes for nutrients or shares pest pressure. In short-season gardens, interplanting companions at transplant time maximizes each bed's productive weeks.
Frequently Asked Questions
When should I plant radish in Duluth, MN?
In Duluth (Zone 4b), direct sow radish around April 2–12. Soil must be at 40°F or warmer at 2-inch depth before sowing — cold soil rots the seeds.
What zone is Duluth, MN for radish growing?
Duluth is USDA Zone 4b. For radish, this means a frost-free growing season of roughly 21 weeks running from May 7 to October 1. Cool-season crops like radish thrive in this zone with both spring and fall planting windows available.
When is radish harvest season in Duluth?
Expect the first radish harvest in Duluth around April 24, with harvest continuing through May 2. This is based on 22–30 days from transplant or direct sow. A fall crop planted August 27–September 6 adds a second harvest around September 18.
How long does it take to grow radish in Duluth, MN?
From transplant or direct sow to first harvest, radish takes 22–30 days in Duluth's climate. Based on a typical planting date of April 2–12, expect your first harvest around April 24. Duluth's cooler Zone 4b climate often lands at the slower end of this range — cooler nights slow fruit development.
What soil does radish need in Duluth?
Duluth's clay-loam soil is productive for radish but benefits from annual compost amendment. Work 2–3 inches of compost into the top 10 inches before planting. Avoid working wet soil in spring — clay-loam compacts badly when wet. Consistent watering paired with organic mulch maintains the even moisture these soils hold well.