GrowingHQ
VegetablebrassicaStraightforward

Kohlrabi

Brassica oleracea

A swollen stem that sits on the soil surface rather than in it, ready in eight to ten weeks and far quicker than any other brassica. Sweet and crisp when picked small; woody and disappointing when left to reach the size the packet photograph suggests.

Position
Full sun or Partial shade
Water
moderate demand
Drainage
Free-draining, Moisture-retentive
Grows to
30–40 cm × 25–30 cm
Hardiness
H4
Harvest
June to October
Difficulty
Straightforward

August

Harvest

Kohlrabi’s year

Resolved for United Kingdom (general). Every window is stored against a climate event rather than a date, so a late frost pocket runs later than the band shows. What else August calls for.

ActivityJFMAMJJASOND
Sow outdoorsApril. May. June. July.
HarvestJune. July. August. September. October.

Timing that travels

The band above resolves this plant's windows into months for one region. These are the windows themselves, stored against a climate event rather than a date — which is the form that survives being carried to a colder garden, a frost pocket, or next year.

Conditions it needs

Light
Full sun, Partial shade
Frost
Hardy
Hardiness rating
H4 (RHS)
Grows best at
15–22 °C
Germinates at
10–25 °C
Soil
Loam, Sandy
Soil pH
6.5–7.5
Drainage
Free-draining, Moisture-retentive
Water needs
moderate
Drought
poor tolerance
Waterlogging
moderate tolerance
Heat
moderate tolerance
Wind and exposure
good tolerance
Where these figures come from
LightSourced guidancemoderate confidence
  • Royal Horticultural Society: Kohlrabi — position

Checked 2026-08-13

FrostSourced guidancehigh confidence
  • Royal Horticultural Society: Kohlrabi — hardiness

Checked 2026-08-13

Hardiness ratingSourced guidancemoderate confidence
  • Royal Horticultural Society: RHS hardiness ratings

Checked 2026-08-13

Grows best atSourced guidancemoderate confidence
  • Royal Horticultural Society: Kohlrabi — temperature

Checked 2026-08-13

Germinates atSourced guidancemoderate confidence
  • Royal Horticultural Society: Seed germination temperatures

Checked 2026-08-13

SoilSourced guidancemoderate confidence
  • Royal Horticultural Society: Kohlrabi — soil

Checked 2026-08-13

Soil pHSourced guidancemoderate confidence
  • Plant Finder — Missouri Botanical Garden: Brassica oleracea — culture

Checked 2026-08-13

DrainageSourced guidancemoderate confidence
  • Royal Horticultural Society: Kohlrabi — soil

Checked 2026-08-13

Water needsHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

DroughtHorticultural consensusmoderate confidence

A check makes it woody, which is irreversible.

No external citation — see the evidence type above.

Checked 2026-08-13

WaterloggingHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

HeatHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Wind and exposureHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

On your soil

Computed by comparing this plant's recorded requirements against each soil's recorded characteristics. A recorded horticultural fact overrides the comparison where GrowingHQ holds one.

SoilVerdictWhy
Heavy clayWorks, with one conditionKohlrabi will crop on heavy clay, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. A plant that stays in the ground through winter with its roots in cold, saturated soil rots — which is what kills most of what fails on heavy ground, rather than the cold.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse.
SandyWorks, with one conditionKohlrabi will crop on sandy, but one thing has to be dealt with first. It has little drought tolerance and this soil dries out fast — it will check and bolt in the first dry spell without watering.Water and mulch will carry it through. On this soil the watering is not optional in a dry spell, which is the difference between a crop and a failure.
Chalky and alkalineWorks, with one conditionKohlrabi will crop on chalky and alkaline, but one thing has to be dealt with first. It has little drought tolerance and this soil dries out fast — it will check and bolt in the first dry spell without watering.Water and mulch will carry it through. On this soil the watering is not optional in a dry spell, which is the difference between a crop and a failure.
LoamPrefers this soilLoam suits Kohlrabi as it stands: The pH suits it: it wants 6.5 to 7.5, and this soil is in that range. The free drainage is exactly what it wants. Loam is among the soils it is recorded as suiting. The soil holds moisture, which saves a great deal of watering.
SiltyPrefers this soilSilty suits Kohlrabi as it stands: The pH suits it: it wants 6.5 to 7.5, and this soil is in that range. The free drainage is exactly what it wants. The soil holds moisture, which saves a great deal of watering.
Peaty and acidWorks, with one conditionKohlrabi will crop on peaty and acid, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. A plant that stays in the ground through winter with its roots in cold, saturated soil rots — which is what kills most of what fails on heavy ground, rather than the cold.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse.
Shallow over rockWorks, with one conditionKohlrabi will crop on shallow over rock, but one thing has to be dealt with first. It has little drought tolerance and this soil dries out fast — it will check and bolt in the first dry spell without watering.Water and mulch will carry it through. On this soil the watering is not optional in a dry spell, which is the difference between a crop and a failure.
Made ground and urban soilWorks, with one conditionKohlrabi will crop on made ground and urban soil, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. A plant that stays in the ground through winter with its roots in cold, saturated soil rots — which is what kills most of what fails on heavy ground, rather than the cold.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse.

Not sure which you have? Four hand tests will settle it.

Space and spacing

Mature height
30–40 cm
Mature spread
25–30 cm
Rooting depth
30 cm
Spacing
25–30 cm apart
Where these figures come from
Mature heightHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Mature spreadHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Rooting depthHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

SpacingSourced guidancemoderate confidence
  • Royal Horticultural Society: Kohlrabi — spacing

Checked 2026-08-13

How far apart to plant kohlrabiThree kohlrabi plants drawn in a row at their recorded spacing of 25–30 cm between plants. The spacing is drawn to scale against a one metre rule; the plants themselves are symbols rather than scale drawings, so the distance between them is the part to read.25–30 cm
Measured centre to centre. Plants set closer than this compete for light and water long before they look crowded, and the crowding cannot be undone once they are in.

In a container

Minimum volume
10 litres or more
Minimum depth
25 cm
Where the container figures come from
Minimum volumeHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Minimum depthHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Suits a container well because it is shallow-rooted and quick. Keep the compost evenly moist or the swollen stem splits.

Where and how you can grow it

Each way of growing is assessed separately, and “not assessed” is a real answer rather than a gap we have filled in with a guess.

MethodSuitabilityWhat it needs
Open groundWell suited
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

Traditional dug bedWell suited
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

Raised bedWell suited
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

ContainerWell suited
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

10 litres; 25 cm deep
GreenhouseWorkable
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

PolytunnelWorkable
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

HydroponicsWorkable
source

GrowingHQ editorial positionmoderate confidence

The one brassica worth a soilless system: it swells a stem rather than a root, which means it needs no depth, and it does it in eight weeks.

  • GrowingHQ editorial synthesis — GrowingHQ

Checked 2026-08-13

WindowsillMarginal
source

Horticultural consensusmoderate confidence

  • Royal Horticultural Society: Growing herbs and salads indoors

Checked 2026-08-13

Growing it

  • ThinningThin early to about 25 cm. Kohlrabi swells above ground and crowded plants simply stay small — there is no later opportunity to correct it.
  • WateringWater steadily rather than heavily. The stem turns woody after a check, and woodiness cannot be reversed by watering afterwards.
  • FeedingCompost worked in before sowing is sufficient. Kohlrabi is grown fast and eaten young, and a plant that is fed hard simply grows past the tender stage — pick them at the size of a golf ball to a tennis ball rather than growing them on.
  • HarvestingPull or cut when the swollen stem is between the size of a golf ball and a tennis ball. Left longer it goes woody and fibrous, and unlike most root crops it does not improve with size — successional sowings a fortnight apart give a longer supply than one bed left to stand.
Where this guidance comes from
ThinningSourced guidancehigh confidence
  • Royal Horticultural Society: Kohlrabi — care

Checked 2026-08-13

WateringSourced guidancehigh confidence
  • Royal Horticultural Society: Kohlrabi — care

Checked 2026-08-13

FeedingSourced guidancemoderate confidence
  • Royal Horticultural Society: Kohl rabi — cultivation

Checked 2026-08-13

HarvestingSourced guidancemoderate confidence
  • Royal Horticultural Society: Kohl rabi — harvesting

Checked 2026-08-13

Is it worth putting under cover?

Whether it will grow there is on the methods table above. This is whether the space is well spent, which is a different question and usually the one being asked.

StructureWhat protection is worthWhat decides it
GreenhouseExtends the season
source

GrowingHQ editorial positionmoderate confidence

What protection is worth for this crop, judged against the same standard as every other record in this file.

  • GrowingHQ editorial synthesis — GrowingHQ

Checked 2026-08-13

Speed. Fast enough to justify the ground for an early sowing, unlike its slower brassica relatives.
PolytunnelExtends the season
source

GrowingHQ editorial positionmoderate confidence

What protection is worth for this crop, judged against the same standard as every other record in this file.

  • GrowingHQ editorial synthesis — GrowingHQ

Checked 2026-08-13

Speed.

On a windowsill

Does not work indoors
source

GrowingHQ editorial positionmoderate confidence

How long the crop is actually productive on an ordinary British windowsill without added light.

  • GrowingHQ editorial synthesis — GrowingHQ

Checked 2026-08-13

 Not a windowsill crop. The reason is given — usually light, root volume or sheer size. Light. A swollen stem needs full sun to form at all, and an indoor plant makes leaves and no bulb.

Growing it without soil

Nearly anything can be grown in a soilless system by somebody with enough equipment. The useful question is whether it is worth it, in which technique, and what goes wrong.

Works with conditions

Succeeds when the conditions listed here are met and fails when they are not. The conditions are the answer, not a caveat.

source

GrowingHQ editorial positionmoderate confidence

The one brassica worth a soilless system: it swells a stem rather than a root, which means it needs no depth, and it does it in eight weeks.

  • GrowingHQ editorial synthesis — GrowingHQ

Checked 2026-08-13

Worth knowing because it is so unexpected: kohlrabi behaves like a leafy crop in a system and like a root crop in the ground.

Techniques that suit it

  • Ebb and flowA bed of inert medium floods and drains on a timer. The medium holds moisture between floods, which makes it far more tolerant of interruption than NFT.
  • Drip-fed mediumSolution is dripped into an inert medium around each plant. The most forgiving technique and the one that suits large, long-season, heavy crops.
  • Deep water cultureRoots hang in aerated solution. Very productive and very unforgiving of solution temperature — warm solution holds less oxygen and root disease follows.
source

Horticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Root space
Modest — the swollen part sits above the medium rather than in it.
pH band
5.5–6.5
Where these figures come from
Root spaceHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

pH bandSourced guidancehigh confidence

Outside roughly this band, individual nutrients become unavailable even when they are present in the solution — which is why a crop can starve in a full reservoir.

  • Purdue Extension — Purdue University: Hydroponic solution management — pH

Checked 2026-08-13

What actually goes wrong

  • Warm solution. Above roughly 22 °C the water holds much less dissolved oxygen and root disease follows quickly, which is why summer is harder than winter in an indoor system.
    source

    Sourced guidancemoderate confidence

    • Purdue Extension — Purdue University: Solution temperature and dissolved oxygen

    Checked 2026-08-13

  • pH drift. The solution moves as the plants take nutrients up, and by the time deficiency symptoms appear on the leaves the cause is several weeks old.
    source

    Sourced guidancehigh confidence

    • Purdue Extension — Purdue University: Hydroponic solution management — pH

    Checked 2026-08-13

No nutrient recipes here

GrowingHQ records pH bands, which are measurable properties of nutrient availability, and deliberately records no EC or PPM targets and no mixing instructions. Published targets vary by cultivar, growth stage, water source and technique, and the figures that apply to your system are on the product you bought.

Harvesting

  • When it is readyPull when the swollen stem is between a golf ball and a tennis ball. Beyond that it turns woody, and no amount of cooking recovers it.
  • How to pick itCut the swollen stem through just above soil level with a knife rather than pulling it, and trim the leaves off leaving a short stub. Take them small — anything above about 8 cm across is usually woody, and the difference between tender and fibrous is a matter of a week or two.
  • Keeping itA few weeks in a fridge. Best eaten within days of pulling.
Where the harvest guidance comes from
When it is readySourced guidancehigh confidence
  • Royal Horticultural Society: Kohlrabi — harvesting

Checked 2026-08-13

How to pick itSourced guidancehigh confidence
  • Royal Horticultural Society: Kohlrabi — harvesting

Checked 2026-08-13

Keeping itHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

What goes wrong

ProblemHow oftenNotes
Cabbage root flycommon
source

Horticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Transplants are the vulnerable stage; a collar or mesh at planting is the control.
Flea beetlecommon
source

Horticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Pits the seedling leaves in a dry spring; a crop past four true leaves outgrows it.
Clubrootoccasional
source

Horticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Slugs and snailscommon
source

Horticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Cabbage white caterpillarsoccasional
source

Horticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Sources for this page

GrowingHQ editorial synthesis · Plant Finder · Royal Horticultural Society

Each figure on this page carries its own citation, under the “where these figures come from” note in its section. Record last reviewed 2026-08-14.