When to Plant Kohlrabi in Idaho (2026 Guide)
Kohlrabi is a unique and nutritious vegetable that thrives in the cool conditions found in Idaho's climate, making it a popular choice among local gardeners. With its crisp, juicy texture and flavor reminiscent of a sweet broccoli stem, kohlrabi can be enjoyed raw in salads or cooked in a variety of dishes. Understanding when to plant this versatile crop is key to successful harvests, especially given Idaho's varying frost dates that range from May 6 to June 12 depending on the USDA hardiness zone.
In Idaho, the timing for planting kohlrabi will depend heavily on your specific zone. For example, if you live in Boise or Caldwell (Zone 5b), your last spring frost typically occurs around May 6, allowing for an earlier spring planting. Conversely, in areas like Idaho Falls, where the frost-free season is shorter (Zone 5a), the last spring frost is usually around May 25, meaning you’ll need to adjust your planting schedule accordingly to ensure a successful crop.
With a frost-free season lasting about 155 days in Zone 5b, and only about 116 days in Zone 5a, it's essential to plan your kohlrabi planting effectively, utilizing both the spring and fall seasons. In areas where the first fall frost arrives as early as September 18, like in Blackfoot and Idaho Falls, recognizing the ideal planting times for kohlrabi can yield a bountiful harvest before the colder nights set in. Being prepared will allow you to enjoy this delightful vegetable all season long.
Planting Schedule by USDA Zone in Idaho
| Zone | Indoor start | Transplant out | Direct sow | Harvest |
|---|---|---|---|---|
| Zone 5b | Start February 15 – March 1, ~6–8 weeks before May 6 | Transplant outdoors April 10 – April 25 | Direct sow April 10 – May 6 | Harvest from June 25 – August 1 |
| Zone 5a | Start March 15 – April 1, ~6–8 weeks before May 25 | Transplant outdoors May 1 – May 15 | Direct sow May 1 – May 25 | Harvest from July 15 – September 1 |
| Zone 4b | Start April 1 – April 15, ~6–8 weeks before June 12 | Transplant outdoors May 20 – May 30 | Direct sow May 20 – June 12 | Harvest from August 1 – August 30 |
Kohlrabi Planting Windows in Idaho
- Indoor start: For Idaho growers, start kohlrabi indoors from February 15 to April 1, depending on your hardiness zone.
- Transplant outdoors: Transplant kohlrabi outdoors between April 10 and May 30, based on your location within Idaho.
- Harvest: Kohlrabi harvest can occur between June 25 and September 1, ensuring the bulbs reach optimal size.
Common Mistakes Growing Kohlrabi in Idaho
- Many Idaho gardeners mistakenly plant kohlrabi too late in the season, risking damage from the first fall frost which can occur as early as September 18. Timing your planting correctly based on your zone's frost dates is essential for a successful harvest.
- Some gardeners in Idaho overlook the importance of soil quality for kohlrabi. Given Idaho's often alkaline soil, it's advisable to amend the soil with compost to ensure the best possible growth conditions.
- Kohlrabi can easily suffer from pest issues, particularly if not monitored closely. Neglecting to check for common pests like aphids or cabbage worms can lead to rapid damage, which is a common mistake among new growers.
- Underestimating the light requirements for kohlrabi is another mistake. Although it can tolerate some heat, it thrives best with at least 6 hours of sunlight daily. Gardeners should ensure their plants receive adequate sun during the crucial growing period.
- Finally, many Idahoans forget that kohlrabi is an excellent candidate for interplanting. By not utilizing the spaces between slower-growing crops like tomatoes or peppers, they miss opportunities to maximize their garden's productivity.
Frequently Asked Questions
What if I'm in a cold pocket of Idaho?
If you're in a colder region, focus on starting kohlrabi indoors as early as possible to get a jump on the growing season. Pay special attention to your local microclimate, as this can make a significant difference in your planting success.
Can I still plant kohlrabi in May?
Yes, in some parts of Idaho, especially in Zone 5a, planting kohlrabi in May can still yield reasonable results. Be sure to pick a date prior to the last frost to give your kohlrabi the best chance for success.
How should I prepare my soil for kohlrabi?
Kohlrabi prefers well-draining, nutrient-rich soil. Adding compost will improve soil structure and increase nutrient content, promoting healthier growth. Consider conducting a soil test to adjust pH if needed.
Do I need to thin my kohlrabi plants?
Yes, thinning your kohlrabi seedlings ensures that they have enough space for healthy growth. Aim for 6 to 8 inches between each plant to allow for optimal bulb development and air circulation.
Why are my kohlrabi bulbs becoming woody?
Woody kohlrabi bulbs usually indicate over-maturity or stress due to heat or drought. Harvest your kohlrabi once buds reach about 3 inches in diameter, and make sure to provide consistent moisture throughout the growing season.
Keep Learning
City guides in Idaho
Other crops in Idaho
Typical fall sowing window for Kohlrabi in Idaho: July 29 – August 19.