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How to Grow Kohlrabi: Fast, Hardy and Best Picked Small

Kohlrabi swells above ground in 45 to 60 days. Pick it at tennis ball size — left longer it goes woody, which is why most people dislike it.

By Zakaria 3 min read Save to Pinterest — opens Pinterest in a new tab
Kohlrabi bulb garden
Photo: utroja0, Pixabay Content License, via Pixabay
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Kohlrabi is quick, hardy and genuinely easy. The reason people dislike it is almost always the same: it was left on the plant too long. Pick at tennis ball size and it is crisp and sweet; pick it at grapefruit size and it is wood.

Sow in the cool, not the heat

Two windows, and one to avoid
SowingHarvestNotes
Spring, 4–6 wks before last frostEarly summerGood. Beat the heat
Midsummer—Avoid. Bolts, goes woody
Late summerAutumnBest flavour — cool finish

Kohlrabi is a cool-season brassica. In heat it bolts — sends up a flower stem — and the bulb coarsens at the same time.

Sow a short row every two to three weeks rather than one long row. It matures fast and all at once, so successional sowing is what turns it from a glut into a supply.

The harvest size rule

This matters more than anything else on the page.

Two to three inches across. Tennis ball. At that size the flesh is crisp, mild and sweet — somewhere between an apple and a broccoli stem, good raw.

Left to keep swelling, the centre becomes fibrous and the flavour turns harsh. A grapefruit-sized kohlrabi is not a bigger harvest, it is a worse one.

The exception is the giant storage varieties — Superschmelz and similar — which are bred to stay tender at a much larger size. If you are growing a standard variety, pick small.

Mesh at sowing, not after

Flea beetles shred brassica seedlings into lace within days, and cabbage whites arrive later. Fine insect mesh over hoops, fitted when you sow, excludes both and removes any need to spray.

Kohlrabi seedlings are small and fast — a flea beetle attack in week one can end the row before it establishes.

Water is the texture

The other cause of woodiness is irregular watering. A plant that dries hard and is then soaked lays down tough growth rings, and that texture does not cook out.

  • About an inch a week, more in heat
  • Mulch once seedlings are established, to even out soil moisture and keep roots cool
  • Direct sow rather than transplant, since root disturbance is another check that coarsens the bulb

Do not earth it up

Kohlrabi is a swollen stem, not a root. It sits on the surface with leaves radiating from it.

People reach for the hoe out of habit with root crops and bury it — which causes rot. It needs no support and no earthing up.

Use the leaves

The plant makes a lot of foliage for a fairly small bulb, and the leaves are as good as kale, slightly milder.

Young leaves whole; strip older ones off their midribs. Treating them as a crop rather than waste roughly doubles what the bed returns.

Step by step

Time
P55D
Cost
10
You need
Kohlrabi seed, Compost, Mulch
Tools
Insect mesh, Hand fork

  1. Sow in spring or late summer, not midsummer

    Kohlrabi is a cool-season brassica. Sow four to six weeks before the last frost for a spring crop, or in late summer for autumn. Midsummer sowings bolt and go woody.

  2. Choose a sunny bed with steady soil

    Six hours of sun and plenty of compost. Kohlrabi is fast-growing and needs consistent moisture and fertility to swell smoothly rather than in fits and starts.

  3. Sow half an inch deep

    Direct sowing is better than transplanting, since any root check during growth is one of the causes of a woody bulb. Sow a short row every two to three weeks for a continuous supply.

  4. Thin to 4 to 6 inches apart

    Closer than most brassicas, because you are growing a swollen stem rather than a head. Crowding gives small bulbs, so thin properly rather than leaving them bunched.

  5. Cover with insect mesh at sowing

    Flea beetles shred brassica seedlings and cabbage whites follow later. Mesh fitted before anything arrives is far more effective than treating afterwards.

  6. Water consistently, about an inch a week

    This is the single biggest factor in texture. A plant that dries out and is then soaked produces a tough, fibrous bulb that no amount of cooking rescues.

  7. Mulch once seedlings are established

    Mulch evens out soil moisture and keeps the roots cool, both of which slow bolting in warm spells.

  8. Do not earth up the swelling bulb

    Kohlrabi swells above the soil line. Burying it causes rot, and it does not need support — this is a stem, not a root vegetable.

  9. Harvest at 2 to 3 inches across

    Tennis ball size, usually 45 to 60 days from sowing. This is the step that decides whether you enjoy it; larger bulbs turn woody and bitter.

  10. Cut at the base and keep the leaves

    Slice the stem at soil level. The leaves are edible and cook like kale, so there is no reason to compost them.

Common questions

How long does kohlrabi take to grow?

Forty-five to sixty days from sowing for most varieties, which makes it one of the quicker brassicas and an easy crop to fit between others. Purple varieties are usually a week or so slower than green ones, and autumn sowings take longer than spring ones because they mature into shortening days. Sowing a short row every two to three weeks gives a continuous supply rather than a glut.

When should you harvest kohlrabi?

When the bulb is two to three inches across — roughly tennis ball size — and no larger. This is the single most important thing about growing it. Left to swell further, the bulb becomes woody and fibrous at the centre and develops a harsher flavour, which is why so many people who have tried kohlrabi once did not enjoy it. The giant varieties sold as storage types are the exception and stay tender larger.

Why is my kohlrabi woody?

Three causes, and the first is much the most common. Leaving it too long before harvesting, which lets the bulb become fibrous. Inconsistent watering, where the plant dries out and is then soaked, producing tough growth rings. And heat, which pushes the plant toward bolting and coarsens the texture. Consistent moisture of about an inch a week, mulch, and picking at tennis ball size address all three.

How far apart should kohlrabi be spaced?

Four to six inches apart in rows about a foot apart, which is closer than cabbage or broccoli because you are growing a single swollen stem rather than a large leafy head. Crowding beyond that gives small bulbs, so thin seedlings properly rather than leaving them in clumps. Giant storage varieties need more room, around eight to twelve inches.

Can you eat kohlrabi leaves?

Yes, and they are good — the leaves cook much like kale or collards, with a similar texture and a slightly milder flavour. Use the young ones whole and strip the tougher older leaves off their midribs. Since the plant produces a substantial amount of foliage alongside a fairly small bulb, eating the leaves roughly doubles what you get from the space.

Does kohlrabi grow above or below ground?

Above ground. The edible part is a swollen stem rather than a root, and it sits on the soil surface with leaves radiating from it, which often surprises people expecting something like a turnip. Do not earth it up or bury it — covering the bulb causes rot and it needs no support. The roots run below it in the normal way.

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