Fertilising guide
How to fertilise Kohlrabi (Brassica oleracea var. gongylodes)— schedule & NPK
Also called German turnip, Turnip cabbage.
More about kohlrabi
About Kohlrabi
Brassica oleracea var. gongylodes · also called German turnip, Turnip cabbage · edible
Kohlrabi is a fast, easy brassica grown for its swollen, globe-shaped stem that sits above ground, with a crisp, mild, turnip-meets-cabbage flavour. Green and purple types crop in 8-10 weeks. Sow successionally from spring, keep it growing steadily in fertile, moist soil and full sun, and harvest while the bulbs are young and tender, before they turn woody.
Growth habit: Low, compact plant with a cluster of long-stalked leaves rising from a smooth, rounded stem that swells just above soil level into the edible 'bulb'.
Watch for — Cabbage root fly: Larvae feed on roots, wilting and stunting young plants. Fit brassica collars around stems at transplanting or use insect-proof mesh to block egg-laying.
What fertiliser kohlrabi actually wants — and why
Kohlrabi is grown entirely for its leaves, so nitrogen is the priority — steady, nitrogen-leaning feeding keeps it growing fast, tender and unbolted.
A nitrogen-leaning feed (higher first number) or compost-rich soil — nitrogen drives the fast, tender leafy growth this crop is grown for. Phosphorus and potassium matter far less here than for fruiting crops.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for kohlrabi: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed kohlrabi, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For kohlrabi:
Moderate feeder. Work a balanced general fertiliser into the bed before sowing. On poorer soils, a single nitrogen side-dressing as plants establish keeps growth steady; avoid excess nitrogen, which delays bulbing and grows leaves at the expense of the stem. In practice: a balanced or compost-rich start, then a nitrogen side-dress or liquid feed every 3-4 weeks through the cropping period in the main season (spring through early autumn).
The dormant-season rule matters more than the exact interval: skip feeding entirely when kohlrabi is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for kohlrabi
Use the vegetable-feed label rate for kohlrabi. Steady availability matters more than a strong dose — a check in growth makes leaves tough and can trigger bolting.
Feeding always goes onto already-damp soil, never dry roots — water kohlrabi first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the kohlrabi watering schedule.
Signs you are over-feeding kohlrabi
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for kohlrabi:
- Very soft, floppy, dark-green growth that attracts aphids.
- Excess leafy growth at the expense of hearts/heads in cabbage and the like.
- Salt crust and scorched leaf edges in containers; nitrate-heavy leaves.
Signs you are under-feeding kohlrabi
- Pale, yellow-green leaves, oldest first, and slow growth.
- Small, tough, bitter leaves and premature bolting.
- Weak, stunted heads in cabbage, broccoli and cauliflower.
If the symptoms point at watering, light or roots rather than nutrition, the full kohlrabi care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
For container-grown kohlrabi, water until it drains freely each time and flush pots monthly with plain water to stop nitrogen salts accumulating; in the ground, good compost levels naturally buffer this.
Organic vs synthetic feeds for kohlrabi
Organic options
Well-rotted manure or compost dug in, plus nitrogen-rich liquid feeds like diluted chicken-manure pellets or nettle feed. UK: pelleted chicken manure or Westland; US: Espoma Garden-tone or blood meal. Steady and soil-building.
Synthetic / liquid feeds
A balanced feed at planting then a high-nitrogen liquid or granular side-dress — UK: Growmore then a nitrogen feed or Phostrogen; US: a 10-10-10 then a high-N (e.g. 21-0-0) side-dress or Miracle-Gro.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising kohlrabi — frequently asked questions
What fertiliser does kohlrabi need?
A nitrogen-leaning feed (higher first number) or compost-rich soil — nitrogen drives the fast, tender leafy growth this crop is grown for. Phosphorus and potassium matter far less here than for fruiting crops. Kohlrabi is grown entirely for its leaves, so nitrogen is the priority — steady, nitrogen-leaning feeding keeps it growing fast, tender and unbolted.
How often should I feed kohlrabi?
Moderate feeder. Work a balanced general fertiliser into the bed before sowing. On poorer soils, a single nitrogen side-dressing as plants establish keeps growth steady; avoid excess nitrogen, which delays bulbing and grows leaves at the expense of the stem. Moderate feeder. Work a balanced general fertiliser into the bed before sowing. On poorer soils, a single nitrogen side-dressing as plants establish keeps growth steady; avoid excess nitrogen, which delays bulbing and grows leaves at the expense of the stem. In practice: a balanced or compost-rich start, then a nitrogen side-dress or liquid feed every 3-4 weeks through the cropping period in the main season (spring through early autumn).
What strength of feed for kohlrabi?
Use the vegetable-feed label rate for kohlrabi. Steady availability matters more than a strong dose — a check in growth makes leaves tough and can trigger bolting.
What does over-feeding kohlrabi look like?
Very soft, floppy, dark-green growth that attracts aphids. Excess leafy growth at the expense of hearts/heads in cabbage and the like. Salt crust and scorched leaf edges in containers; nitrate-heavy leaves. Letting kohlrabi run short of nitrogen mid-crop is the main mistake — growth checks, leaves toughen and brassicas/leafy greens bolt or turn bitter. Keep nitrogen steadily available.
Should I flush the soil of kohlrabi?
For container-grown kohlrabi, water until it drains freely each time and flush pots monthly with plain water to stop nitrogen salts accumulating; in the ground, good compost levels naturally buffer this.
Keep reading
- Kohlrabi care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water kohlrabi — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise tomato
- How to fertilise pepper
- How to fertilise cucumber
- All 1284 fertilising guides in the Growli library