Growing kohlrabi in USDA Zone 6 means gardening with about six frost-free months and winters that drop to -10 to 0°F. The average last spring frost falls in the range Apr 1–15 and the average first autumn frost in the range Oct 15–Nov 1. Those are USDA/NOAA zone averages, not promises for any one garden — check your local extension service for your own dates. Kohlrabi is the brassica that looks like a small green sputnik and tastes like a mild, sweet cross between cabbage and broccoli stem. In Zone 6 it is one of the easiest cool-season crops to grow, because it shrugs off light frost and matures fast enough for both a spring and a fall crop.
When to plant kohlrabi in Zone 6
Kohlrabi tolerates light frost, so it can go out ahead of the tender crops in Zone 6. Start indoors four to six weeks before the average last frost (Apr 1–15) and transplant in late March to mid-April, once seedlings are sturdy, or direct sow around the last frost. Either way, keep cover ready for a hard freeze, which is different from a light frost and can still damage young plants.
| Step | Zone 6 timing | Notes |
|---|---|---|
| Start indoors | Early–mid-Mar | 7–10 days to germinate; strong light, warm soil |
| Direct sow (spring) | Late Mar–early Apr | Sow thinly; keep the seedbed damp until seedlings appear |
| Transplant outdoors | Late Mar–mid-Apr | Harden off for a week first; keep fleece ready for a late frost |
| First harvest | late May | 50–60 days to maturity from sowing/transplanting |
| Fall / succession sow | By early August | Only if the crop matures before the first frost (Oct 15–Nov 1) |
The table is worked out from the Zone 6 frost averages and the crop's own figures: 50–60 days to maturity and 7–10 days to germinate. Dates are ranges, not single days, so use the frost date calculator for your own garden. The planting calendar hub shows the same timing for every Zone 6 month, and Zone 6 March covers what else is happening that month.
Starting kohlrabi: indoors or direct?
Sow seed directly where it will grow, or start it indoors in modules and transplant the young plants out while they are still small. Kohlrabi dislikes being moved once it is large, so if you start indoors, move seedlings out when they have two or three true leaves and handle the roots gently. Give seedlings the strongest light you can and harden them off for a week before they go outside. Work out exact sowing dates with the seed-starting calculator.
Soil, spacing and sun
Kohlrabi grows best in soil that holds moisture but drains freely, enriched with well-rotted compost before sowing. A steady supply of moisture matters more than heavy feeding: plants that dry out and then get a sudden soaking often split or turn woody. Kohlrabi grows best in full sun, in soil with a pH of 6.0–7.5. Dig in well-rotted compost before planting to improve drainage and moisture holding. Space plants 6–9 inches apart — it is tempting to crowd plants in, but crowded plants stay small and invite disease. Kohlrabi belongs to the Brassicaceae family, so avoid planting it where the same family grew last year.
Watering and feeding
Water little and often rather than flooding the bed once a week. Aim for evenly moist soil through the whole growing period, and mulch with straw or shredded leaves to keep the roots cool and damp in warm spells. Kohlrabi needs moderate water overall. Water deeply and less often rather than lightly every day, water at the base in the morning so leaves dry before night, and mulch to keep the soil evenly moist.
Companion planting
Good companions for kohlrabi include marigolds, basil, onions, lettuce. Planting kohlrabi near Zone 6 Rutabaga works well too, since the two crops share similar timing in this zone. Compare with Zone 5 Kohlrabi, where the same crop runs a little later.
Pests and problems
Watch for cabbage white butterfly caterpillars on the leaves and flea beetles making small shot-holes in young plants. Pick caterpillars off by hand, cover young plants with insect mesh, and keep the bed free of brassica weeds that harbour pests. The common pests and problems to watch for with kohlrabi are cabbage worms, aphids, flea beetles, slugs. Inspect plants regularly and act early: hand-pick larger pests, wash aphids off with water, and remove badly affected leaves.
Harvesting and storing kohlrabi
Cut the swollen stem when it is still young and tender, while the skin is smooth and the flesh is crisp. Plants left too long in the ground turn woody and fibrous, so check the bed every few days once the stems start to swell and harvest little and often. Twist off the leaves and store the stems in a cool place or in the fridge, where they keep for several weeks. The leaves are edible too — cook them like spring greens rather than throwing them away. Sow a short row every two to three weeks in spring for a steady supply instead of one big sowing that all matures at once.
Fall and succession planting
Sow a fall crop in late summer so the stems size up in the cool autumn weather; kohlrabi sown then often tastes sweeter than the spring crop, and light frost improves the flavour rather than damaging it. Count forward 50–60 days from any sowing date and check it against the average first frost of Oct 15–Nov 1.
Frequently asked questions
When should I plant kohlrabi in Zone 6?
Sow or start kohlrabi in spring around the average last frost (Apr 1–15), so plants are established well before the first autumn frost (Oct 15–Nov 1). Kohlrabi is frost-tolerant and takes 50–60 days to maturity, which fits the Zone 6 season. Check your local extension service for your own dates.
Can I grow kohlrabi in Zone 6?
Yes. Kohlrabi is frost-tolerant, needs 50–60 days to maturity, and takes 7–10 days to germinate, which fits inside the Zone 6 frost-free season from Apr 1–15 to Oct 15–Nov 1. Give it full sun and soil with a pH of 6.0–7.5, and it should do well.
How far apart should I space kohlrabi?
Space plants 6–9 inches apart, in full sun and soil with a pH of 6.0–7.5. Crowding slows growth and invites disease.
What pests affect kohlrabi in Zone 6?
The most common are cabbage worms, aphids, flea beetles, slugs. Inspect plants regularly, especially the undersides of leaves, hand-pick larger pests, wash aphids off with a strong jet of water, and remove badly affected leaves early. Healthy, well-spaced plants in good soil resist pests better than stressed ones.
When do I harvest kohlrabi in Zone 6?
Allow 50–60 days to maturity from sowing or transplanting, which puts the main harvest around late May for a spring planting. Harvest at the stage for your variety and gather everything usable before the first frost (Oct 15–Nov 1).