Kohlrabi
Brassica oleracea var. gongylodes
Swollen-stemmed brassica, quick and mild — herbs at its feet keep moths off.
Spacing & sowing
- Plant spacing
- 9.8 in
- In-row spacing
- 7.9 in
- Between rows
- 11.8 in
- Square-foot density
- 4 per square
- Sow depth
- 0.2 in
Calendar (from your frost dates)
- Sow indoors
- 28 days before the last spring frost
- Sow direct
- 14 days before the last spring frost
- Plant out
- at the last spring frost
- First harvest
- 45 days after the last spring frost
- Harvest ends
- 7 days after the first fall frost
Growing
- Type
- Vegetable · Grown as an annual
- Botanical family
- Brassica (cabbage family)
- Sunlight
- Full sun
- Watering
- Moderate
- Soil
- Fertile, moisture-retentive
- Feeding
- Leafy greens & lawns
- Frost tolerant
- Yes
- Cool-season crop
- Yes — takes a second fall window
- Season
- Cool Season
- Harvest type
- Single Harvest
- Start from
- seed
Growth stages
- 7 d Germination
- 55 d Harvest
Harvest
- When
- Fast varieties are ready 40–60 days from sowing; spring sowings mature in early summer and late-summer sowings crop in autumn, when light frost sweetens them. Don't leave spring crops standing in heat — they turn woody quickly.
- What to look for
- The swollen stem should be 5–8 cm in diameter (tennis-ball size at most for standard varieties) with fresh, upright leaves; giant storage varieties like Superschmelz stay tender much larger. Cracked or softball-plus bulbs of ordinary varieties will be woody and hot.
- How to harvest
- Cut the stem just below the swollen globe with a sharp knife, or pull the whole plant and trim off roots and leaves. The young leaves are edible — treat them like kale rather than discarding.
- How often
- A single harvest per plant; pull each one as it reaches size rather than waiting for the whole row, since individual plants size up unevenly. Sow short rows every 2–3 weeks for a continuous supply.
- Storing the crop
- Remove the leaves (they drain moisture), and refrigerate trimmed globes in a perforated bag for 2–4 weeks. Autumn crops store 2–3 months in a cold shed or in damp sand in a root cellar; peel before use as the skin thickens in storage. Diced or grated flesh can be blanched and frozen.
Pests & problems
- Aphids Small sap-sucking insects — greenfly, blackfly — that cluster on soft new growth and excrete sticky honeydew. Squash by hand, hose off with water, and encourage ladybirds and lacewings.
- Cabbage root fly White maggots eat the roots of young brassicas, which wilt blue-tinged and collapse. Fit collars around stems at planting and grow under insect mesh.
- Cabbage white caterpillars Green or mottled caterpillars of the white butterflies that skeletonize brassica leaves in summer. Net crops with fine mesh before the butterflies lay and pick off caterpillars and yellow eggs.
- Flea beetle Tiny jumping beetles that pepper seedling leaves with shot-holes, worst on brassicas and rocket in dry spells. Keep seedlings growing fast with steady water and cover with fine insect mesh.
- Slugs & snails Ragged holes and silvery trails on seedlings and soft young growth, worst in damp weather. Use beer traps, wool pellets, or torchlight hand-picking; keep beds clear of daytime hiding places.
- Clubroot A soil disease that swells and distorts brassica roots; plants wilt and stunt. Lime the soil toward pH 7, improve drainage, and rest infected ground from brassicas for years.
Garden allies
Beneficial predators that hunt this plant's pests — grow their favourite flowers nearby to recruit them. companion plant
- Garden birds Passeriformes
Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray.
- Beneficial nematodes Steinernema & Heterorhabditis spp.
Microscopic worms watered onto damp soil that hunt down soil-dwelling grubs and release a bacterium that kills them within days. Timing is the whole thing: warm, damp soil and a small target grub, which means late summer for most of what they are used against.
- Big-eyed bug Geocoris spp.
A stubby 3 mm bug with enormous wrap-around eyes, working the soil surface and the low foliage for aphids, mites, thrips and insect eggs. It is the main natural check on chinch bugs in a lawn and it is killed outright by insecticide.
- Damsel bug Nabidae
A slender, mantis-armed bug that grabs aphids, small caterpillars, and thrips in low crops and meadowy edges. Leave a strip of unmown grasses and flowers for it to overwinter in.
- Ground beetle Carabidae
Fast, glossy night hunters that patrol the soil surface for slugs, cutworms, and root-fly larvae. Give them daytime cover — thick perennial edges, stepping stones, a log — and skip the tillage that wrecks their burrows.
- Parasitic wasps Braconidae & Trichogramma
Tiny, stingless wasps that lay eggs in or on caterpillars, aphids, and moth eggs — the white cocoons riding a hornworm are their calling card, so leave that caterpillar be. Umbel flowers with shallow nectar keep the adults fuelled.
- Rove beetle Staphylinidae
Slim, quick beetles with short wing cases that hunt in soil and litter, taking root-fly eggs and larvae, fungus-gnat larvae, and mites. Mulch and undisturbed ground keep them resident year-round.
- Spiders Araneae
Webs, ambushes, and night patrols make spiders the garden’s steadiest generalist predators, taking whatever flies or crawls past. Mulch, ground cover, and undisturbed corners keep the population dense.
- Aphid midge Aphidoletes aphidimyzaHunts Aphids
A tiny midge whose orange maggots paralyze aphids and drink them dry, twenty or more each. Sold as a greenhouse biological control and resident outdoors wherever there are small nectar flowers and an unsprayed aphid colony to find.
- Assassin bug ReduviidaeHunts Aphids
A patient ambusher with a curved beak it drives into whatever it catches — caterpillars, beetles, bugs, and the occasional bee, so count it a generalist rather than a specialist. It will jab a careless finger too, so admire it and leave it be.
- Centipedes ChilopodaHunts Slugs & snails
Flat, fast, one pair of legs to a segment — and a predator, unlike the slow round millipede it is constantly confused with. It hunts slugs, cutworms, springtails and woodlice by night under mulch and stones. Learn the difference and leave this one alone.
- Dragonflies & damselflies OdonataHunts Aphids
Aerial hunters that take mosquitoes, midges and small flies on the wing all day, and whose larvae spend a year or more clearing the same insects from the water. A pond with planted margins and no fish is the way to have them.
- Frogs & toads AnuraHunts Slugs & snails
A resident toad works the beds every night for slugs, cutworms, and weevils. Recruit them with water — even a sunken basin pond — plus damp shade and an upturned-pot toad house; skip the slug pellets that poison their prey.
- Green lacewing Chrysoperla carneaHunts Aphids
Its bristly larvae — "aphid lions" — impale aphids, mealybugs, thrips, and mite colonies, eating hundreds a week. Adults feed on nectar and pollen from small open flowers and overwinter in hollow stems left standing.
- Hedgehog Erinaceus europaeusHunts Slugs & snails
A European animal, and worth saying so plainly: there are no hedgehogs in North America, and the ally that does the same night shift here is the toad, the opossum or the ground beetle. Where they do occur, cut a gap in the fence and skip the pellets.
- Hoverfly SyrphidaeHunts Aphids
Bee-mimicking flies whose legless larvae graze aphid colonies clean while the adults pollinate. A ribbon of shallow, nectar-rich flowers kept in bloom all season recruits wave after wave of them.
- Ladybird (lady beetle) CoccinellidaeHunts Aphids
The gardener’s favorite ally: adults and their alligator-shaped larvae each eat thousands of aphids, plus scale, mealybugs, and other soft-bodied sap-suckers. Grow flat, open flowers for the adults and never spray a colony that ladybird larvae are already working.
- Minute pirate bug Orius spp.Hunts Aphids
A pinhead-sized true bug that is the best natural check on thrips, and happily spears aphids, mites, and insect eggs too. It needs pollen when prey is scarce, so keep something flowering nearby.
- Praying mantis MantidaeHunts Aphids
A sit-and-wait ambusher that snatches caterpillars, beetles, and anything else that wanders close — friend and foe alike, so count it a mixed blessing. Tall, structured plantings give it perches and egg-case anchors.
- Salamanders & newts CaudataHunts Slugs & snails
Damp-loving hunters of slugs, worms, woodlice and beetle larvae that spend the day under a log or a stone and work the beds at night. Companions to the toads: they want the same damp shade, the same log pile, and the same absence of slug pellets.
- Snakes & lizards Colubridae & PhrynosomatidaeHunts Slugs & snails
A garter snake works the beds for slugs and voles and a fence lizard clears grasshoppers off a sunny wall. Almost every snake a gardener meets is harmless and useful; give them a log pile, a warm flat stone and a bit of cover and they stay.
- Soldier beetle CantharidaeHunts Aphids
Soft-winged beetles seen mating on flower heads in high summer; adults and larvae both take aphids and soft grubs. Open composite flowers are their landing pads and hunting grounds.
Germination & growth
- Germination temp
- 59–77°F
- Min soil temp
- 43 °F
- Photoperiod
- long day
Companion planting
Good neighbors
Keep apart
Did you know?
The swollen 'bulb' you eat is a fat stem sitting above the soil — its name means 'cabbage-turnip'.
The Cottage Garden Companion — the gardener's herbarium at cottagegardencompanion.com