Repotting guide

When & how to repot Kohlrabi 'Kossak' (Brassica oleracea var. gongylodes 'Kossak')

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.

Mature size: Bulbs commonly 15-20 cm across (up to 25 cm / several kg); plant 30-45 cm tall.

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

How to tell kohlrabi 'kossak' needs repotting

Repotting on a calendar is less reliable than reading the plant. For kohlrabi 'kossak', watch for these signs:

Flowering has tailed off year on year and the clump has become congested and overcrowded.
Lots of leaf and few flowers — a classic sign that kohlrabi 'kossak' bulbs or tubers need lifting and dividing.
Bulbs visibly bursting the pot or pushing each other to the surface.
It is the natural dormancy window (foliage yellowed and died back) — the only safe time to lift and split.

For the underlying biology of a pot-bound root system and why it stalls a plant, see our guide to spotting and fixing a root-bound plant.

How often to repot kohlrabi 'kossak'

Lift and divide every 3–4 years once clumps congest. Rather than a true repot, kohlrabi 'kossak' is lifted and divided once the clump congests and flowering drops off. 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..

What size pot to step kohlrabi 'kossak' up to

Pot size matters less than depth and spacing here. When you replant kohlrabi 'kossak', set the bulbs or tubers at the correct depth (a rough guide: two to three times their own height of soil over the top) and space them so they are not touching. A wide, shallow pot suits a clump better than a tall narrow one.

Not sure of the exact diameter? Our pot size calculator takes the current pot and root spread and tells you the right next size — it deliberately recommends a single step up, never a big jump.

The best time of year to repot kohlrabi 'kossak'

The only safe window is dormancy: wait until the foliage has yellowed and died back naturally, lift and divide then, and replant before or at the start of the next growing season. Disturbing kohlrabi 'kossak' in full growth or flower sets it back badly.

Step-by-step: repotting kohlrabi 'kossak'

Wait for dormancy. Let kohlrabi 'kossak' foliage yellow and die back completely. Lifting while it is in growth wastes the energy it is storing for next year.
Lift carefully. Loosen the soil well away from the bulbs/tubers with a fork and ease the whole clump out without spearing them.
Separate the offsets. Gently pull the clump apart into individual bulbs or tubers. Keep only firm, healthy, blemish-free ones.
Replant at the right depth. Reset them in fresh fertile, firm, well-drained loam at the correct depth and spacing — not touching — so each has room to bulk up.
Water in and rest. Water once to settle them, then keep on the dry side until growth resumes. Do not feed until leaves are actively growing.

Aftercare

After replanting kohlrabi 'kossak', keep the soil barely moist — not wet — until shoots appear; bulbs and tubers rot in cold, saturated soil. Once leaves are growing strongly, resume normal watering. Hold off feeding until the plant is in active growth again.

The right soil mix for kohlrabi 'kossak'

Kohlrabi 'Kossak' wants fertile, firm, well-drained loam. Rich, organic soil, pH 6.0-7.5, firmed to support bulb development. Lime acidic soils toward neutral against clubroot. Needs depth; suits raised beds more than small pots. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting kohlrabi 'kossak' — frequently asked questions

How often should you repot kohlrabi 'kossak'?

Lift and divide every 3–4 years once clumps congest for kohlrabi 'kossak'. Kohlrabi 'Kossak' is lifted and divided, not "repotted". Every 3–4 years, once the foliage has died back and it is dormant, lift the clump, separate the offsets, and replant at the correct depth in fertile, firm, well-drained loam. Crowding, not pot size, is what reduces flowering over time.

What size pot does kohlrabi 'kossak' need?

When is the best time of year to repot kohlrabi 'kossak'?

Do you "repot" kohlrabi 'kossak', or lift and divide it?

You lift and divide it. Kohlrabi 'Kossak' grows from bulbs or tubers, so instead of repotting you wait for dormancy, lift the congested clump, separate the healthy offsets, and replant them at the right depth and spacing. Doing this every 3–4 years restores flowering.

Should you fertilise kohlrabi 'kossak' after repotting?

Hold off feeding kohlrabi 'kossak' until it is in active growth again. Fresh soil already carries enough nutrients to get it re-established, and feeding disturbed roots too soon does more harm than good.