Kohlrabi is the vegetable that looks like a joke and tastes like a treat: a swollen stem that sits above the ground like a little green sputnik, crisp, mild and sweet, like a cross between a turnip and a cabbage stem. Eaten raw it is one of the best snacks in the garden; cooked, it is delicate and buttery.
It takes 50–60 days to mature and it is frost-tolerant, so it is a spring and autumn crop, sown in succession for a steady supply. It is also one of the easiest brassicas to grow — and one of the most forgiving.
Kohlrabi at a glance
| Growing factor | What kohlrabi need |
|---|---|
| Sun | full sun |
| Soil pH | 6.0–7.5 |
| Days to germination | 7–10 |
| Days to maturity | 50–60 |
| Spacing | 6–9 inches |
| Water needs | moderate |
| Cold tolerance | frost-tolerant |
| Family | Brassicaceae |
Starting seeds
Kohlrabi can be started indoors or sown direct, and either route works well. Indoors, sow in trays or cells and expect germination in 7–10 days; direct-sown seed goes into prepared soil once conditions are right for the crop. Starting indoors buys you a few weeks of season and gives steadier germination, while direct sowing is simpler and avoids transplant shock.
Choose the method that fits your season length: short-season gardens in Zones 3–5 gain the most from starting indoors, while Zones 8–10 can usually direct-sow with confidence. Our seed-starting calculator works out indoor sowing dates from your frost dates, and your local extension service can confirm what works in your area.
Kohlrabi can be started indoors or sown direct, with germination in 7–10 days. For a spring crop, start indoors in late winter in Zones 3–6, or direct-sow in spring in Zones 7–9; for autumn, sow in midsummer — in Zones 6–8 sow in late summer, in Zones 9–10 in autumn, and in frost-free Zones 11–13 sow in the cool season. Sow in trays or direct, thinning to the final spacing once seedlings have a few true leaves. Sow little and often, since the bulbs are best picked young.
Transplanting and planting out
Set plants out 6–9 inches apart when they have three or four true leaves, in firm soil — kohlrabi, like all brassicas, prefers a firm bed. Water them in well and mulch to hold moisture. Transplant on a cloudy day and handle seedlings gently, since a checked plant bolts or produces a woody bulb. Space them properly: crowded kohlrabi stays small and woody.
When you set plants out, space them 6–9 inches apart — that spacing is what the mature plant needs, and crowding is one of the commonest causes of small harvests. Our plant-spacing calculator works out how many plants fit your bed, and the square-foot garden planner can lay the bed out for you. Harden seedlings off for a week before planting out, moving them outside for longer each day, and plant on a cloudy day or in the evening so they do not wilt in their first hours outdoors.
Soil and feeding
Kohlrabi wants fertile, moisture-retentive soil at pH 6.0–7.5, with compost dug in before planting. It is a moderate feeder, so a little balanced fertiliser at planting time is enough — too much nitrogen gives leaves instead of bulbs. Like all brassicas, it should not follow another brassica in the same bed. A firm, weed-free bed matters, since kohlrabi competes badly with weeds when young.
Aim for a soil pH of 6.0–7.5 — a simple soil test will tell you where you stand, and garden lime or sulfur can nudge pH up or down over a season. Feed lightly and steadily rather than in one heavy dose: too much fast nitrogen late in the season pushes leafy growth at the expense of the part you eat. Our fertiliser calculator works out amounts for your bed size, and the raised-bed soil calculator and soil-volume calculator tell you how much mix a new bed needs. A mulch layer after planting keeps the soil moist and cool and feeds the soil as it breaks down.
Watering
Water needs are moderate: keep the soil evenly moist through the growing season, watering deeply when the top inch or two dries out. Deep, infrequent watering builds deeper roots than a daily sprinkle, and it keeps the plants steady through dry spells.
Water needs are moderate, but kohlrabi must not dry out while the bulb is swelling — drought gives small, woody bulbs, and a dry spell followed by heavy rain splits them. Water deeply and evenly, and mulch to hold moisture in. In a dry summer, water twice a week; in a wet one, leave them alone. Even watering is the whole secret of a tender bulb.
Water at the base of the plant, in the morning, so the leaves dry quickly and the water reaches the roots instead of evaporating off the surface. A soaker hose or drip line is ideal. Our watering calculator gives a starting point for your bed size and soil, and the watering schedule generator can build a routine around it. Mulch is your best friend here: a few inches of straw or shredded leaves cuts evaporation and keeps moisture even between waterings.
Sunlight and temperature
Kohlrabi needs full sun for the best growth, though it tolerates light shade. It is frost-tolerant, so spring and autumn sowings take light frosts in their stride, and a light frost sweetens the bulbs. In Zones 8–10 it grows through winter; in frost-free Zones 11–13 grow it in the coolest months, since heat makes it bolt and turns the bulbs woody.
This crop is rated frost-tolerant for cold tolerance, so plan your season around that: hardy and frost-tolerant crops can be sown and harvested around frosts, while tender crops need warm soil and frost-free nights. Our sunlight calculator can check whether your spot gets enough sun through the season, and the hardiness-zone finder will confirm your zone. If your summers run very hot, afternoon shade or a shade cloth can keep a cool-season crop productive for a few extra weeks.
Pests and diseases
Kohlrabi attracts the usual brassica pests, though the bulb sits above ground and escapes some soil problems. The ones to expect are cabbage worms, aphids, flea beetles and slugs.
- Cabbage Worms — green caterpillars that chew holes in leaves. Pick them off by hand and grow under fine mesh from planting day.
- Aphids — cluster on young leaves. Wash them off with water and encourage ladybirds.
- Flea Beetles — tiny beetles that pepper young leaves with shot-holes. Keep seedlings covered and watered — vigorous plants outgrow the damage.
- Slugs — chew young seedlings in damp weather. Pick them off at dusk and keep the bed clear of debris.
Inspect plants weekly, especially the undersides of leaves, and act early — a small problem caught in time is a hand-picked handful of pests, while a late one can cost the crop. Row cover keeps many flying pests off young plants, and healthy, well-watered plants resist attack far better than stressed ones. If you need help identifying what you are seeing, our pest-identifier helper and plant-disease checker walk through the symptoms.
Companion plants
Kohlrabi grows well with marigolds, basil, onions and lettuce. It is a compact plant, so it fits well between slower crops, filling gaps while they establish, and lettuce can be grown in its shade. Marigolds help keep soil pests down. As a brassica, it should not follow another brassica in the same bed.
Good companions for kohlrabi include:
- Marigolds
- Basil
- Onions
- Lettuce
Our companion-planting finder can suggest more pairings for your bed plan. As a general rule, avoid planting members of the same family (Brassicaceae) in the same spot year after year — rotate beds so soil-borne problems do not build up.
Harvesting
Harvest when the bulbs are the size of a tennis ball, from about 50 days after sowing — pull the whole plant and cut off the leaves, leaving a short stem. Do not wait for a big bulb: oversized kohlrabi turns woody and fibrous, and a tennis-ball bulb is at its sweetest. Peel the tough outer skin before eating, and use the young leaves too — they cook like collards.
Expect the crop to be ready about 50–60 days after sowing, though weather and variety shift that window by a week or two either way. Our harvest-date calculator works out your expected harvest date from your sowing date, and the vegetable-yield estimator can estimate how much a bed should produce. Harvest in the morning when plants are cool and crisp, and use a sharp knife or secateurs rather than tearing, which damages the plant and invites disease.
Common problems and fixes
| Problem | Likely cause | Fix |
|---|---|---|
| Woody bulbs | left too long or drought | Pick at tennis-ball size; water evenly. |
| Split bulbs | drought followed by heavy rain | Water evenly and mulch. |
| Bolting to seed | heat or transplant shock | Sow in cool weather; transplant young seedlings gently. |
Woody bulbs
Likely cause: left too long or drought A woody kohlrabi is one that was picked too late or went short of water while swelling. Pick young, water evenly, and do not let the plant get old — the best bulb is a young bulb.
Split bulbs
Likely cause: drought followed by heavy rain Bulbs split when a dry spell is followed by heavy rain, as the bulb swells faster than the skin can stretch. Even watering and a mulch layer prevent it.
Bolting to seed
Likely cause: heat or transplant shock Kohlrabi bolts when stressed by heat or by a seedling left too long in a tray. Sow for the cool season, transplant while seedlings are young, and keep the soil moist.
Frequently asked questions
When do I harvest kohlrabi?
When the bulbs are tennis-ball sized — about 50–60 days after sowing. Don't wait for a big bulb: oversized kohlrabi turns woody and fibrous.
What does kohlrabi taste like?
Crisp, mild and sweet, like a cross between a turnip and a cabbage stem. Eat it raw in salads or cook it — it is delicate and buttery.
Do I peel kohlrabi?
Yes — peel the tough outer skin before eating. The young leaves can be cooked like collards.
Why is my kohlrabi woody?
It was picked too late or went short of water while the bulb was swelling. Pick young, at tennis-ball size, and water evenly.
Can I grow kohlrabi in a container?
Yes — it is compact and ideal for pots. One plant per gallon of compost, kept well watered, in full sun.