Fertilising guide

How to fertilise Kohlrabi 'Kossak' (Brassica oleracea var. gongylodes 'Kossak')— schedule & NPK

Also called Kossak kohlrabi, giant kohlrabi.

More about kohlrabi 'kossak'

About Kohlrabi 'Kossak'

Brassica oleracea var. gongylodes 'Kossak' · also called Kossak kohlrabi, giant kohlrabi · edible

Kohlrabi 'Kossak' is a giant storage kohlrabi forming swollen, pale-green stem bulbs that can reach grapefruit size while staying crisp and sweet rather than woody. Bred for size and excellent storage, it crops in roughly 60-80 days, holds in the ground or cold store for months, and resists the toughness that plagues oversized standard kohlrabi.

Growth habit: Forms a large, round, swollen stem bulb sitting above soil level with a crown of upright leaves; this cultivar stays tender at unusually large sizes.

Watch for — Clubroot: Swollen, deformed roots and stunted bulbs in infected soils. Rotate brassicas, lime to near-neutral pH, and improve drainage.

What fertiliser kohlrabi 'kossak' actually wants — and why

Kohlrabi 'Kossak' stores its crop underground, so the rule is the reverse of leafy plants — go easy on nitrogen, which sends energy into tops at the expense of roots.

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 'kossak': 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 'kossak', 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 'kossak':

Moderate-to-heavy feeder: prepare soil with compost or balanced fertiliser, then feed every 3-4 weeks; balanced nutrition (not excess nitrogen) favours firm, sweet bulbs over leafy tops. In practice: prepare the bed with well-rotted compost (not fresh manure), then little or no extra feeding through the season (spring through early autumn); a light potassium feed mid-growth at most.

The dormant-season rule matters more than the exact interval: skip feeding entirely when kohlrabi 'kossak' 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 'kossak'

Less is more for kohlrabi 'kossak'. If you feed at all, keep it light and low-nitrogen — the soil preparation does the work, and over-feeding actively spoils the crop.

Feeding always goes onto already-damp soil, never dry roots — water kohlrabi 'kossak' first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the kohlrabi 'kossak' watering schedule.

Signs you are over-feeding kohlrabi 'kossak'

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for kohlrabi 'kossak':

Large lush leafy tops and small, forked or hairy roots.
Split or cracked roots from a nitrogen-and-water surge.
All foliage and no usable crop at harvest.

Signs you are under-feeding kohlrabi 'kossak'

Genuinely uncommon in reasonable soil — these are not hungry plants.
Pale, weak tops and small roots only in very poor, exhausted ground.
Slow growth across the whole bed in long-uncultivated soil.

If the symptoms point at watering, light or roots rather than nutrition, the full kohlrabi 'kossak' care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

Flushing is not the issue for kohlrabi 'kossak' — the equivalent care is avoiding fresh manure and high-N feeds entirely, and rotating beds so the soil is not over-rich from a previous hungry crop.

Organic vs synthetic feeds for kohlrabi 'kossak'

Organic options

Well-rotted compost worked in the season before, or for a previous crop, is ideal — never fresh manure. UK: garden compost, low-N blends; US: Espoma Garden-tone sparingly or finished compost. Lean and well-worked beats rich.

Synthetic / liquid feeds

If anything, a low-nitrogen, potassium-leaning feed only — UK: a high-potash feed mid-season at most, never a general high-N; US: a 5-10-10 sparingly. Most root crops crop best with no synthetic feed at all.

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 'kossak' — frequently asked questions

What fertiliser does kohlrabi 'kossak' need?

Low-nitrogen, with modest phosphorus and potassium for root development — ideally compost-improved soil rather than a high-N feed. Excess nitrogen forks the roots and grows lush tops instead of a crop. Kohlrabi 'Kossak' stores its crop underground, so the rule is the reverse of leafy plants — go easy on nitrogen, which sends energy into tops at the expense of roots.

How often should I feed kohlrabi 'kossak'?

Moderate-to-heavy feeder: prepare soil with compost or balanced fertiliser, then feed every 3-4 weeks; balanced nutrition (not excess nitrogen) favours firm, sweet bulbs over leafy tops. Moderate-to-heavy feeder: prepare soil with compost or balanced fertiliser, then feed every 3-4 weeks; balanced nutrition (not excess nitrogen) favours firm, sweet bulbs over leafy tops. In practice: prepare the bed with well-rotted compost (not fresh manure), then little or no extra feeding through the season (spring through early autumn); a light potassium feed mid-growth at most.

What strength of feed for kohlrabi 'kossak'?