When to Plant Kohlrabi in Wisconsin (2026 Guide)
Kohlrabi is an excellent crop for gardeners in Wisconsin, providing crisp and flavorful bulbs ready for harvest in just 45–60 days. With a frost-free season lasting approximately 177 days in Zone 6a and 149 days in Zone 5b, there are plenty of opportunities for both spring and fall plantings. Understanding the right timing for planting based on your local frost dates, such as the median last spring frost on April 25 for Zone 6a and May 6 for Zone 5b, is essential for a successful harvest.
This unique brassica, resembling a swollen stem above the soil line, is not just eye-catching but also versatile. It thrives in cooler weather and tolerates frost, enabling Wisconsin gardeners to plant it in both spring and late summer. Whether you're in Milwaukee or Madison, knowing when to start kohlrabi indoors, transplant outdoors, and expect to harvest can maximize your garden's productivity throughout the growing season.
In addition to its adaptability, kohlrabi takes up minimal space, making it ideal for interplanting with other crops. Its robust flavor allows it to shine in both raw and cooked dishes, from salads to stir-fries. As you plan your garden in Wisconsin, it's crucial to align your planting schedule with regional frost dates to ensure the success of this rewarding vegetable.
Planting Schedule by USDA Zone in Wisconsin
| Zone | Indoor start | Transplant out | Direct sow | Harvest |
|---|---|---|---|---|
| Zone 6a | Start February 15 – March 1, ~6–8 weeks before April 25 | Transplant outdoors April 10 – April 20, after last frost | Direct sow March 25 – April 10, after soil warms | Harvest from June 1 – June 15, when bulbs reach 3 inches |
| Zone 5b | Start March 1 – March 15, ~6–8 weeks before May 6 | Transplant outdoors April 25 – May 5, past last frost | Direct sow April 10 – April 25, after soil warms | Harvest from June 15 – June 30, when bulbs are 3 inches |
| Zone 5a | Start March 15 – March 30, ~6–8 weeks before May 19 | Transplant outdoors May 5 – May 15, after last frost | Direct sow April 25 – May 5, after soil warms | Harvest from July 1 – July 15, when bulbs are 3 inches |
Kohlrabi Planting Windows in Wisconsin
- Indoor start: In Wisconsin, start kohlrabi indoors between February 15 – March 30, based on your frost zone.
- Transplant outdoors: Transplant kohlrabi outdoors from late April through mid-May, depending on your local frost dates.
- Harvest: Kohlrabi can be harvested from June through July, once bulbs reach about 3 inches in diameter.
Common Mistakes Growing Kohlrabi in Wisconsin
- One of the most common mistakes in Wisconsin is not accounting for the differing frost dates across zones. Planting too early can expose young plants to unexpected frosts, stunting their growth or killing them.
- Growing kohlrabi during the hottest part of summer is also a mistake many Wisconsin gardeners make. Excessive heat can lead to tougher, woody bulbs. Instead, aim for spring or late summer plantings to capitalize on the cooler conditions kohlrabi thrives in.
- Another common issue relates to soil quality. Wisconsin's clay soil can retain too much moisture, leading to root rot if not amended. Be sure to improve drainage before planting kohlrabi to ensure optimal growth conditions.
- Neglecting to thin seedlings properly can hinder kohlrabi growth as the plants compete for nutrients. Make sure to space your plants appropriately after germination, providing each bulbing stem ample room to grow without crowding.
- Wisconsin's inconsistent weather patterns mean late spring snows can disrupt kohlrabi growth. To mitigate this risk, gardeners should be sure to monitor forecasts closely and consider protective covers or cloches to shield young plants if unexpected frosts are predicted.
Frequently Asked Questions
What if I'm in a cold pocket of Wisconsin?
If your garden is situated in a cold pocket, consider starting kohlrabi indoors earlier than recommended. Also, use row covers to protect the plants from frost and give them a better chance to thrive.
Can I still plant kohlrabi in May?
Yes, in Zone 5b, you can still plant kohlrabi in early May, but do so before the median last frost on May 6. It’s best to directly sow seeds or transplant starts that are ready to go.
How much space do I need for kohlrabi?
Kohlrabi requires about 6–12 inches between plants, ensuring they have enough room to grow. This spacing allows for ideal bulb development and prevents overcrowding, leading to better quality harvests.
Is kohlrabi frost-tolerant?
Yes, kohlrabi is quite frost-tolerant. This makes it an excellent choice for gardeners in Wisconsin, as it can withstand cooler temperatures and be sown in early spring or late summer for fall harvests.
When should I harvest kohlrabi?
Harvest kohlrabi when bulbs are around 3 inches in diameter for the best flavor and texture. Waiting too long can lead to woody, fibrous bulbs that are less enjoyable to eat.
Keep Learning
City guides in Wisconsin
Other crops in Wisconsin
Typical fall sowing window for Kohlrabi in Wisconsin: July 30 – August 20.