When To Plant Kohlrabi In Zone 5

If you’re gardening in zone 5, knowing when to plant kohlrabi is the key to a successful harvest of this crisp, versatile vegetable. Getting the timing right for both spring and fall crops ensures you get the best flavor and texture from your plants.

Kohlrabi is a cool-season champion, thriving in the mild temperatures of spring and fall. It grows quickly and can handle a light frost, which makes it perfect for our climate. But if you plant it too late in spring, it will turn woody and bitter in the summer heat. Plant it too late in fall, and it won’t mature before a hard freeze. Let’s break down the perfect schedule.

For zone 5 gardeners, the calendar revolves around your average last spring frost and first fall frost dates. These dates can vary, but a common range is around May 15th for the last spring frost and October 15th for the first fall frost. Always check local data for your specific area.

Optimal Spring Planting Timing

The goal for spring is to get kohlrabi established and harvested before the heat of summer sets in. You have two excellent options:

Direct Seed Outdoors: Sow seeds directly into your garden soil 2-4 weeks before your last expected frost date. For a May 15th last frost, aim for mid to late April. The soil should be workable and not soggy.
Transplant Starts: For an even earlier harvest, start seeds indoors 4-6 weeks before your last frost date. This means sowing indoors in late March to early April. Transplant these sturdy seedlings into the garden 1-2 weeks before the last frost date.

A good rule of thumb is to get your main spring crop in the ground by early May at the latest. Succession planting, or sowing a new small row every two weeks, can extend your harvest window.

Optimal Fall Planting Timing

Fall is often the best time to grow kohlrabi in zone 5. The cooling temperatures create ideal conditions for sweet, tender bulbs. The trick is to work backwards from your first fall frost.

Calculate your planting date by finding the “days to maturity” on your seed packet. Most kohlrabi varieties mature in 45-60 days.
Count back from your first fall frost date (e.g., October 15th), and then add an extra 10-14 days as a “fall factor” because plants grow more slowly in shorter, cooler days.

For a 55-day variety with an October 15th frost, you’d count back 55 days to August 21st, then add 14 days, giving you a target planting date of around August 7th. This ensures your bulbs are full-sized before heavy frosts.

You can direct seed or use transplants for fall. If starting seeds in late summer’s heat, keep the seedbed consistently moist for good germination.

Choosing the Right Kohlrabi Varieties

Selecting fast-maturing varieties is smart, especially for fall. Here are some reliable choices for zone 5:

Early White Vienna: A classic, pale green variety ready in about 55 days. Very reliable.
Purple Vienna: Similar to its white cousin but with beautiful purple skin. The interior is still pale green.
Kossak: A giant, later-maturing type (80 days) that stays tender longer. Great for fall storage.
Superschmelz: Another giant variety known for its exceptional sweetness and slow bolting.

Step-by-Step Planting Guide

Prepare the Soil: Kohlrabi prefers loose, fertile, and well-draining soil with a pH between 6.0 and 7.5. Work in several inches of compost before planting.
Sowing Seeds: Plant seeds ¼ to ½ inch deep. Space them about 1 inch apart in rows that are 12-18 inches apart.
Thinning: Once seedlings are a few inches tall, thin them to stand 4-6 inches apart. Crowded plants won’t form good bulbs. You can eat the thinnings in salads!
Transplanting: If using starts, plant them at the same depth they were growing in their container. Space them 4-6 inches apart in the row.

Essential Care Tips for Success

Consistent care is simple but crucial for plump kohlrabi bulbs.

Watering: Provide 1-1.5 inches of water per week. Even moisture is vital; fluctuations can cause the bulbs to crack or become tough.
Fertilizing: A balanced fertilizer at planting time is usually sufficient. If your soil is poor, a side-dressing of a nitrogen fertilizer when plants are half-grown can help.
Weeding & Mulching: Keep the area weed-free to reduce competition. A layer of straw or shredded leaves mulch helps retain soil moisture, suppress weeds, and keep the bulbs clean.
Pest Watch: Watch for cabbage worms and flea beetles. Use floating row covers immediately after planting to exclude these pests effectively.

Harvesting and Storage Tips

Harvest kohlrabi when the bulbs are about 2-3 inches in diameter—roughly the size of a golf ball or tennis ball. They are at their most tender and flavorful then. If you leave them to grow to large, they become woody.

Use a sharp knife to cut the stem just below the bulb. You can also eat the young, tender leaves, which are similar to collard greens. For fall kohlrabi, you can leave them in the ground through several light frosts, which can sweeten the flavor.

For storage, remove the leaves and roots. The bulbs can be stored in a plastic bag in the refrigerator for several weeks. For long-term storage, they can be kept in a cold, humid root cellar.

Common Problems and Solutions

Even with good timing, a few issues can pop up.

Bolting: If plants flower prematurely, it’s usually due to planting too late in spring or a sudden warm spell. Stick to your early schedule and choose bolt-resistant varieties for spring.
Woody Bulbs: This is caused by heat, lack of water, or letting them grow too big. Harvest on time and keep them watered.
Split Bulbs: Irregular watering, especially a heavy rain after a dry period, causes this. Mulching helps maintain even soil moisture.

FAQ: Kohlrabi in Zone 5

Can I plant kohlrabi in summer in zone 5?
It’s not recommended. Summer heat stresses the plant, leading to poor bulb formation, bitterness, and bolting. Focus on spring and fall plantings.

How do I protect my fall kohlrabi from an early frost?
Kohlrabi can handle light frosts. For an unexpected early hard freeze, cover the plants with a frost blanket or old bedsheets overnight to extend the season.

What are good companion plants for kohlrabi?
Plant it with other cool-season crops like beets, onions, lettuce, and cucumbers. Avoid planting it near other brassicas like broccoli if you have persistent pest issues.

My kohlrabi bulbs are tough, what happened?
They were likely harvested too late or experienced to much heat or drought. Next time, note the days to maturity and harvest sooner.

Can I grow kohlrabi in containers?
Absolutely. Choose a pot at least 12 inches deep and wide. Use quality potting mix and be diligent about watering, as containers dry out faster.

By following this zone 5 schedule—planting in early spring as soon as the soil can be worked and again in mid-to-late summer for fall—you’ll enjoy a long season of crisp, sweet kohlrabi. The key is respecting its need for cool weather and keeping a close eye on the calender. With a little planning, you’ll have a fantastic harvest.