Start indoors or direct sow?

Start indoors and transplant for an earlier spring crop, or direct sow for a simple succession planting. Transplant young seedlings before they become root-bound, since stressed plants can form tough or small bulbs.

When to start Kohlrabi seeds

For spring planting, start indoors 4 to 6 weeks before the last spring frost and transplant 2 to 3 weeks before that frost date. Direct sow 2 to 4 weeks before the last frost, or sow in late summer for a fall crop.

How to sow the seeds

Sow seeds 1/4 to 1/2 inch deep in a sterile seed-starting mix. Use individual cells about 1 to 2 inches wide or small plugs, and pot up only if seedlings will outgrow their cells before planting time.

Germination

Seeds usually germinate in 5 to 10 days. A soil temperature of about 60 to 75 F and evenly moist mix encourage quick emergence.

Seedling care

Give indoor seedlings strong light for 14 to 16 hours daily, keeping lights close enough to prevent stretching. Water when the mix begins to dry at the surface, provide air movement, and thin direct-sown plants to 5 to 8 inches apart.

Transplanting & hardening off

Harden seedlings off over 7 to 10 days before planting them into fertile, well-drained soil. Set them at the same depth they grew in their cells and space plants about 5 to 8 inches apart.

Tips

Plant in spring or fall, not during sustained summer heat, for the best texture. Harvest when the swollen stems are roughly 2 to 3 inches across rather than waiting for oversized bulbs.

General seed-starting guidance for US home gardens; timing depends on your local frost dates and variety. Page updated Aug 4, 2026.