Vegetable · Brassicaceae
Kohlrabi
Brassica oleracea Gongylodes Group
Grown fast and cool and picked small, kohlrabi swells a smooth, pale bulb of a stem right on top of the soil.
Full sun
Every 3–7 days
64–75°F · 18–24°C
45–60 days
Overview
Kohlrabi has a shape all its own: a smooth, rounded globe of pale green or deep purple that sits right on the soil, with slender leaf stalks springing straight out of its surface. That globe is the plant's thickened stem, and above it the broad, blue-green leaves fan out on long stalks. The flesh inside is pale, close-grained, and glassy when young, and raw it tastes between a mild turnip and a broccoli stem, crisp and faintly sweet.
It belongs to the cabbage family, the same species as broccoli, kale, and cabbage, only bred to bulge its stem rather than pack a head or a rosette of leaves. As a cool-season crop it fills out fast, often in well under two months, which is why two crops a year are common. Speed shows in the flesh itself: a bulb that swells quickly and gets picked young stays wet and tender, while one that stalls through heat or overgrows turns coarse and stringy.
The whole plant keeps to a compact frame, so the swollen stem and its crown of leaves never crowd a bed. It takes a light frost without a mark on the foliage and wants little more than steady water and honest soil. Timed right, it yields a firm, crisp bulb with skin drawn smooth over pale, juicy flesh.
Care
The short version: full sun and cool weather, steady moisture of about an inch of water a week to keep the pale flesh tender, rich well-drained soil, and a harvest of smooth bulbs taken young at 2 to 3 inches across.
Light
Kohlrabi swells its smoothest, most even bulb in full sun, at least six hours a day. It takes partial shade in hot weather, which cools the plant and slows the growth just enough to keep the stem tender before it bolts.
Water
The plant needs even, consistent moisture, about an inch of water a week, and this shows straight in the flesh. Steady water fills the stem with pale, juicy, tender tissue, while a plant that dries out and recovers turns the flesh tough, woody, and bitter.
Soil
Kohlrabi roots into loamy, well-drained soil rich in organic matter, the kind that feeds a fast, smooth-skinned bulb. A pH of 6.0 to 7.5 suits it, and holding toward the higher end guards against clubroot, the disease that knots the roots of the cabbage family.
Temperature
The crop keeps its flesh crisp in cool air between 64°F and 75°F (18°C to 24°C). Light frost leaves the foliage unmarked, but heat coarsens the stem, since warm spells drive it to bolt and toughen the bulb.
Humidity
Ordinary outdoor humidity is enough, so there is no figure to chase. What shapes the crisp, wet flesh is steady soil moisture, and that is what keeps the pale interior firm.
Feeding
A balanced or low-phosphorus fertilizer worked into the bed at planting feeds the swelling stem, guided by a soil test where you can. A side-dressing of nitrogen once the plants stand about 4 inches tall keeps the leaves broad and the bulb filling fast.
Pruning
Kohlrabi needs no pruning, and the crown of leaf stalks is left whole on the plant. Only lower leaves gone ragged and yellow from pests or disease are pulled off and discarded.
Size & spacing
The whole plant stays low, reaching just 6 to 12 inches (15 to 30 cm) tall and about as wide, the swollen stem sitting close to the soil under its fan of leaves. Standard varieties space about 4 inches (10 cm) apart, giving each smooth bulb room to round out without touching its neighbor.
When to plant
Kohlrabi is a cool-weather crop that sulks in summer heat. A spring sowing gives a late-spring harvest, and a July sowing swells the bulbs into the cool of fall. Each crop rounds out in well under two months.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: early spring, 4 to 6 weeks before transplanting outdoors
- Plant: mid-April to early May for spring crop, or July for fall crop
- Harvest: harvest when the swollen stem reaches 2 to 3 inches in diameter
Hardiness
USDA hardiness zones: 3–9
Temperature: down to -40°C
Troubleshooting
Most kohlrabi trouble shows plainly on the plant, in the flesh of the stem or the surface of the leaves, and it traces back to timing and the cabbage-family pests it shares with its relatives. Read the sign on the plant early and it is easy to head off. Match what you see below, then act before the bulb or the leaves take real damage.
Limp leaves above swollen, distorted roots
The leaves go limp and the plant stops filling out, and the reason waits underground. Lift it and the roots show either the fine, dark tunnels of cabbage maggots or the swollen, club-shaped galls of clubroot twisting the normal fine roots into knots. An infected plant will not recover, so it is pulled and destroyed, brassicas rotate on a four-year cycle, and a higher soil pH keeps clubroot in check.
Fix:
- Remove and destroy affected plants
- Practice a 4-year rotation away from brassicas
Woody, stringy flesh inside the bulb
An oversized bulb trades its glassy, juicy flesh for coarse fiber. Slice one and the cut face reads stringy and dull rather than wet and pale, the mark of a stem that swelled past its prime or hardened through heat and drought. A bulb cut at 2 to 3 inches (5 to 8 cm) across from evenly moist soil shows a crisp, close-grained interior instead.
Fix:
- Harvest at 2 to 3 inches in diameter for best quality
- Keep soil evenly moist to maintain fast, uninterrupted growth
Ragged-edged holes torn through the leaves
Torn, irregular holes open across the broad leaf blades, the feeding scars of green caterpillars, most often imported cabbageworms, cabbage loopers, or diamondback moth larvae. The larvae themselves are green and blend into the leaf, tucked against the underside beside crumbs of dark frass. Handpicking, a coat of Bt, and a floating row cover over young plants clear them and keep the moths from laying.
Fix:
- Handpick caterpillars
- Apply Bacillus thuringiensis (Bt) where appropriate
- Use floating row covers
Round pinprick holes across young leaves
Tiny round holes pepper the young leaf blades, each a clean puncture the size of a pinprick, the signature of flea beetles that spring off at the lightest touch. The stippled look is stark on a small seedling but fades as a vigorous plant unfurls fresh, unmarked leaves. A row cover set at planting and steady feeding carry the plant past the pitting.
Fix:
- Use floating row covers at planting
- Maintain vigorous growth so plants outgrow damage
Toxicity
Kohlrabi is completely safe, a food crop with nothing toxic in it for people or animals. Both the smooth swollen stem and the broad leaves are edible, so a nibble from a curious pet is no concern. The only caveat is quantity, since any brassica can cause gas, and a large feed is not ideal for horses.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Kohlrabi is safe for cats. A bite taken from a crisp stem or a leaf blade causes no harm, though most cats sniff at it and turn away.
Dogs None
Dogs handle kohlrabi without trouble, whether they crunch a raw pale chunk or take it plainly cooked. Only a large helping is likely to bring on gas.
Horses Mild
A small piece is fine for a horse, but a large feed of any brassica can upset the gut or, over time, act on the thyroid. It stays an occasional treat.
Rabbits Safe
Rabbits gnaw both the leafy tops and the crisp swollen stem. A slow introduction in small portions lets the gut adjust to a new green.
Livestock Safe
Cattle, goats, and sheep graze kohlrabi safely, cropping the broad leaves and the pale globe alike. As with any brassica, it enters the diet gradually rather than all at once.
Birds Safe
Backyard hens and other birds peck at the leaves and the tough skin of the stem. Nothing in the plant puts them at risk.
People Safe
People eat kohlrabi raw or cooked at any age. The crisp, pale bulb and the green leafy tops are both good food.
As a brassica, large quantities can cause gas or mild goitrogenic effects; horses should not be fed large amounts.
Varieties
Only a handful of kohlrabi varieties reach most seed catalogs, sorted mainly by skin color and the size of the bulb. These are the ones worth knowing.
Purple Vienna
An heirloom whose deep purple skin sheathes flesh that shows pale greenish-white just beneath the surface.
White Vienna
The common pale green form, its crisp, mild flesh close-grained under a smooth light skin.
Kossak
A giant storage type whose flesh stays tender and fine-textured even as the globe swells well past ordinary kohlrabi.
How to propagate
Kohlrabi grows from seed and nothing else, rising from a small round seed into a plant that swells its own edible stem.
SeedEasy
Sow indoors in early spring 4 to 6 weeks before transplanting, or direct sow mid-April to early May and again in July for fall · 7 to 14 days to germinate, with bulbs ready 45 to 60 days from sowing
Kohlrabi rises from small round seed and asks for little. The sowing goes indoors in early spring about 4 to 6 weeks before transplanting, or straight into the ground from mid-April through early May and again in July for fall. Each seed sits 1/4 to 1/2 inches (5 cm) deep, and standard plants thin to 4 inches (10 cm) apart. The first pale sprouts break the soil in 7 to 14 days, and the swelling stems round into pickable bulbs 45 to 60 days from sowing.
Myths
Kohlrabi is a root vegetable like a turnip.
The part you eat rides above the soil, not below it. That rounded globe is a swollen stem, a smooth bulb that balloons out from the base of the plant with leaf stalks springing directly from its surface, not a root pushing down into the ground. The old name German turnip misleads, since kohlrabi is a brassica far nearer to cabbage than to any true turnip.