If you’re gardening in zone 7, knowing when to plant kohlrabi is the key to a successful harvest. This unique vegetable thrives in cool weather, and timing it right means you can enjoy two productive seasons each year.
This guide gives you the optimal timing for planting, along with clear steps to grow crisp, flavorful kohlrabi in your own garden.
When To Plant Kohlrabi In Zone 7 – Optimal Timing For Planting
For zone 7 gardeners, the calendar is your best friend. Kohlrabi grows best when temperatures are between 40°F and 75°F. It bolts, or goes to seed, in hot weather, which makes the stems tough and bitter.
You have two main planting windows: spring and fall. The fall season is often easier and more productive because the cooling temperatures are perfect for growth.
Spring Planting Dates
Your goal for spring is to get kohlrabi established before summer heat arrives. You need to work around the last expected frost.
- Direct Seed Outdoors: Sow seeds directly into your garden soil 4 to 6 weeks before your last average spring frost date. For most of zone 7, this is between mid-February and mid-March.
- Transplanting: Start seeds indoors 6 to 8 weeks before your last frost. This gives you a head start. Harden off seedlings and transplant them into the garden 2 to 4 weeks before the last frost date, when they have a few true leaves.
A common mistake is planting to late in spring. If you wait until April, the plants will likely bolt as soon as the June heat hits.
Fall Planting Dates
Fall is the premier season for kohlrabi in zone 7. The cooling days and longer, cool nights create ideal growing conditions, resulting in sweeter, more tender bulbs.
- Direct Seed for Fall: Count backwards from your first average fall frost date. Sow seeds directly in the garden 8 to 10 weeks before that first frost. For most of zone 7, where the first frost is typically in late October to early November, this means planting in mid-to-late August.
- Succession Planting: To extend your harvest, sow a few seeds every two weeks through early September. This gives you a continuous supply rather than one large glut.
The fall crop often has less pest pressure and grows more consistently than the spring one. The flavor is also notably sweeter after a light frost.
Choosing the Right Kohlrabi Variety
Selecting a variety suited to the season can improve your results. Some types mature faster or handle stress better.
- For Spring Planting: Choose fast-maturing varieties like ‘Quickstar’ or ‘Korridor’ (around 45 days). They’ll be ready before the heat sets in.
- For Fall Planting: You have more options. Slower-maturing, larger varieties like ‘Gigante’ or ‘Superschmelz’ do well, as do reliable standards like ‘Purple Vienna’ or ‘White Vienna’ (50-60 days).
Always check the “days to maturity” on the seed packet and count back from your frost dates to ensure it fits your window.
Preparing Your Garden Soil
Kohlrabi needs fertile, well-draining soil to form those nice, round bulbs. Poor soil leads to woody or misshapen growth.
- Location: Pick a spot that gets full sun (at least 6 hours).
- Soil Test: It’s a good idea to test your soil pH. Kohlrabi prefers a pH between 6.0 and 7.5.
- Amend: Work in 2 to 3 inches of compost or well-rotted manure before planting. This improves drainage and fertility.
- Fertilizer: Mix in a balanced organic fertilizer according to package directions. Kohlrabi is a moderate feeder.
Step-by-Step Planting Guide
Follow these simple steps for planting success, whether from seed or transplant.
- Sowing Seeds: Plant seeds ¼ to ½ inch deep. Space them about 1 inch apart in rows that are 12 to 18 inches apart.
- Thinning: Once seedlings are a few inches tall, thin them to stand 4 to 6 inches apart. Crowded plants won’t form good bulbs. You can eat the thinnings in a salad!
- Transplanting: If using starts, dig a hole just larger than the root ball. Space plants 4 to 6 inches apart in all directions. Plant them at the same depth they were growing in their container.
- Watering: Water gently but thoroughly immediately after planting to settle the soil.
Caring for Your Kohlrabi Plants
Consistent care is simple but crucial for developing those crisp bulbs.
- Watering: Provide 1 to 1.5 inches of water per week. Inconsistent watering causes bulbs to crack or become tough. Using a soaker hose or drip irrigation at the base of the plants is best.
- Mulching: Apply a 2-inch layer of straw or shredded leaves around plants. This conserves moisture, keeps soil cool, and suppresses weeds.
- Fertilizing: If your soil is rich, you may not need more fertilizer. For a mid-season boost, side-dress with a nitrogen-rich fertilizer like fish emulsion when bulbs begin to swell.
- Weeding: Keep the area weed-free. Weeds compete for nutrients and water, which kohlrabi needs to swell properly.
Common Pests and Problems
Kohlrabi is a brassica, so it shares pests with cabbage and broccoli. Vigilance is key.
- Cabbage Worms/Loopers: The green caterpillars that chew holes in leaves. Handpick them daily or use an organic Bt (Bacillus thuringiensis) spray.
- Aphids: Small clusters on undersides of leaves. Blast them off with a strong spray of water or use insecticidal soap.
- Flea Beetles: Tiny jumping beetles that pepper leaves with small holes. Use floating row covers immediately after planting as a physical barrier.
- Bolting: If your plant sends up a flower stalk, it’s usually due to planting too late in spring or a sudden spike in heat. Harvest immediately, as the bulb will become woody. Focus on your fall crop for better results.
Using floating row covers from the day you plant is the easiest way to prevent most insect problems, especialy in the spring.
Harvesting and Storing Your Kohlrabi
Harvesting at the right time ensures the best texture and flavor.
- When to Harvest: Kohlrabi is ready when the bulb is about 2 to 3 inches in diameter—roughly the size of a golf ball or tennis ball. Don’t let them get much larger, or they become fibrous.
- How to Harvest: Use a sharp knife to cut the stem just below the bulb. You can also harvest the young, tender leaves to cook like kale or collards.
- Storing: For short-term use, remove the leaves and store bulbs in a plastic bag in the refrigerator for 2 to 3 weeks. For longer storage, kohlrabi can be chopped and frozen, or stored in a root cellar-like environment.
Frequently Asked Questions (FAQ)
Can I plant kohlrabi in the summer in zone 7?
It’s not recommended. Summer heat causes kohlrabi to bolt quickly and develop poor flavor. Stick to early spring and late summer/fall plantings.
How do I know my exact frost dates for zone 7?
Zone 7 covers a broad area. Use your local zip code in the USDA frost date tool or consult your county extension office for the most accurate last spring and first fall frost dates for your town.
Can I grow kohlrabi in containers?
Absolutely. Choose a pot at least 12 inches deep and wide. Use high-quality potting mix and be diligent about watering, as containers dry out faster. A single plant per large pot is best.
Why are my kohlrabi bulbs not swelling?
This is usually due to overcrowding, inconsistent watering, or insufficient nutrients. Ensure plants are thinned to 4-6 inches apart, water regularly, and start with fertile soil.
Is kohlrabi a perennial plant?
No, kohlrabi is a biennial grown as an annual. It completes its life cycle (seed to flower) over two growing seasons, but we harvest the bulb in the first season.
By following this timing guide, you can enjoy two harvests of this versatile vegetable. The crisp, mild flavor of homegrown kohlrabi is worth the planning. Remember, in zone 7, your fall planting is often the most reliable and flavorful crop you’ll grow.