Minnesota’s cold winters push kohlrabi planting to late May, when the ground has fully thawed. Finding the best time to plant kohlrabi in minnesota is key to a crisp, sweet harvest before summer heat turns it woody.
Kohlrabi is a cool-season crop that thrives in the short, intense springs of the Upper Midwest. If you plant too early, frost can kill seedlings. Too late, and the bulbs become tough and bitter.
This guide gives you exact dates, soil temperature checks, and step-by-step methods for a successful kohlrabi crop in Minnesota.
Best Time To Plant Kohlrabi In Minnesota
The absolute best window for direct sowing kohlrabi seeds outdoors is from mid-May to early June. This timing works for all zones across the state, from the Twin Cities up to Duluth.
You want the soil temperature to be at least 45°F (7°C) but ideally between 50°F and 65°F. Kohlrabi seeds will germinate slowly in cold soil, so waiting until the ground warms is smart.
For a fall harvest, plant a second crop in late July to early August. This avoids the peak summer heat and gives you tender bulbs for autumn soups and salads.
Why Timing Matters So Much In Minnesota
Minnesota has a short growing season, often with a last frost date around May 15 in the south and late May in the north. Kohlrabi is frost-tolerant down to about 25°F, but young plants are vulnerable to hard freezes.
If you plant in early April, a late snowstorm could wipe out your seedlings. Waiting until late May reduces that risk significantly.
Kohlrabi also hates heat. When temperatures consistently hit 80°F, the bulbs stop swelling and turn fibrous. That’s why spring planting is a race against the summer sun.
Soil Temperature: The Real Deciding Factor
Don’t rely only on the calendar. Use a soil thermometer to check your garden bed at 2 inches deep. Here’s what to look for:
- Below 40°F: Seeds will rot or germinate very slowly
- 45°F to 50°F: Germination in 10-14 days, but growth is slow
- 50°F to 65°F: Ideal range, germination in 5-7 days
- Above 75°F: Germination drops off, plants bolt quickly
In most Minnesota gardens, the soil reaches 50°F by mid-May in the south and late May in the north. Check your local extension office for precise soil temperature data.
Frost Dates And Planting Windows By Region
Minnesota spans USDA zones 3a to 4b. Here are typical last frost dates and recommended planting windows:
- Southern MN (zone 4b): Last frost around May 10-15. Plant kohlrabi seeds May 15-25.
- Central MN (zone 4a): Last frost around May 15-20. Plant seeds May 20-30.
- Northern MN (zone 3a-3b): Last frost around May 25-June 1. Plant seeds May 25-June 5.
For fall crops, count back 60 days from your first fall frost (usually mid-September in the north, late September in the south). That puts your second planting around late July to early August.
How To Plant Kohlrabi For Best Results
Now that you know the best time, here’s how to get those seeds in the ground properly.
Step 1: Prepare The Soil
Kohlrabi likes loose, well-draining soil rich in organic matter. Till or dig your bed to 8-10 inches deep. Remove rocks and clumps.
Mix in 2-3 inches of compost or aged manure. Kohlrabi is a heavy feeder, so good soil prep pays off.
The soil pH should be between 6.0 and 7.5. If you have acidic soil (common in Minnesota), add lime a few weeks before planting.
Step 2: Sow Seeds Correctly
Plant seeds ¼ to ½ inch deep. Space them 2 inches apart in rows 12-18 inches apart. You’ll thin them later.
Water the soil gently after planting. Keep it consistently moist but not soggy until seeds germinate.
If you’re transplanting seedlings from indoors, harden them off for 7-10 days before moving them outside. Plant them at the same depth they were in their pots.
Step 3: Thin Seedlings
When seedlings have 2-3 true leaves, thin them to 6-8 inches apart. This gives each plant enough room to form a good-sized bulb.
Don’t skip thinning. Crowded kohlrabi produces small, tough bulbs. You can eat the thinnings in salads.
Step 4: Mulch And Water Consistently
Apply a 2-inch layer of straw or grass clippings around the plants. Mulch keeps soil cool and moist, which kohlrabi loves.
Water deeply once or twice a week, depending on rainfall. Aim for 1-1.5 inches of water per week. Inconsistent watering causes the bulbs to crack.
Fall Planting: A Second Chance For Kohlrabi
Many Minnesota gardeners overlook fall kohlrabi, but it’s often sweeter than spring crops. Cool autumn temperatures concentrate the sugars.
For fall planting, sow seeds directly in the garden 8-10 weeks before your first expected frost. In southern MN, that’s around August 1-10. In northern MN, aim for late July.
Fall kohlrabi can handle light frosts, which actually improve flavor. Harvest after a frost for the sweetest bulbs.
Varieties That Perform Best In Minnesota
Not all kohlrabi varieties are equal in short seasons. Choose these for reliable results:
- Early White Vienna: Matures in 50-55 days, classic mild flavor
- Kolibri: Purple variety, 45-50 days, very cold-tolerant
- Kossak: Large bulbs, 60 days, stores well
- Rapid: Hybrid, 40-45 days, perfect for quick spring crops
Stick with early-maturing varieties for spring planting. For fall, you can try longer-season types like Kossak.
Common Problems And How To Avoid Them
Even with perfect timing, issues can pop up. Here’s what to watch for.
Bolting (Going To Seed)
Kohlrabi bolts when stressed by heat or drought. This ruins the bulb, making it woody and inedible.
Prevent bolting by planting early enough to harvest before July heat. Also, keep soil consistently moist and mulch heavily.
Pests: Flea Beetles And Cabbage Worms
Flea beetles leave tiny holes in leaves. They’re most active in early spring. Use row covers or diatomaceous earth to protect young plants.
Cabbage worms are green caterpillars that eat leaves. Hand-pick them or spray with Bt (Bacillus thuringiensis).
Split Bulbs
Irregular watering causes kohlrabi bulbs to crack. Water deeply and consistently, especially during dry spells.
Mulch helps maintain even soil moisture. If you see cracks forming, harvest immediately—the bulb won’t store well.
Harvesting Kohlrabi At The Right Time
Kohlrabi is ready to harvest when the bulb is 2-3 inches in diameter. That’s about the size of a tennis ball.
Don’t let bulbs get larger than 4 inches. Bigger bulbs are tough, stringy, and less flavorful.
Use a sharp knife to cut the stem just below the bulb. Leave the roots in the ground—they’ll decompose and add organic matter.
Store kohlrabi in the refrigerator for up to 3 weeks. Remove the leaves first, as they draw moisture from the bulb.
Frequently Asked Questions
Can I start kohlrabi indoors in Minnesota?
Yes, start seeds indoors 4-6 weeks before your last frost date. Harden them off gradually before transplanting. This gives you a head start in short seasons.
What happens if I plant kohlrabi too early in Minnesota?
Seeds may rot in cold, wet soil. Seedlings that survive a hard freeze can be stunted or killed. Wait until soil reaches 45°F at least.
Is it too late to plant kohlrabi in July?
For a spring crop, yes. But you can plant a fall crop in late July to early August. Just choose a fast-maturing variety like Rapid.
How do I protect kohlrabi from Minnesota frost?
Use row covers or cloches if a late frost is forecast. Kohlrabi can handle light frosts, but hard freezes below 25°F will damage it.
Can I grow kohlrabi in containers in Minnesota?
Yes, use a pot at least 12 inches deep. Plant one kohlrabi per 6-inch pot. Move containers to a sheltered spot if frost threatens.
Final Tips For Minnesota Kohlrabi Success
Kohlrabi is one of the easiest crops for Minnesota gardens if you get the timing right. The key is patience—wait for warm soil in spring, and plant early enough for fall.
Keep your soil rich and moist. Thin seedlings without guilt. Harvest at the right size for the best flavor.
With these guidelines, you’ll enjoy crisp, sweet kohlrabi from your own garden all season long. Happy planting.