Repotting guide

When & how to repot Konjac (Amorphophallus konjac)

Also called konjac, devil's tongue, elephant yam, konnyaku.

More about konjac

About Konjac

Amorphophallus konjac · also called konjac, devil's tongue · edible

Amorphophallus konjac is a tropical aroid grown for its large starchy corm, the source of glucomannan used to make konnyaku and shirataki noodles. It produces a single tall, dramatically dissected leaf in summer and a dark, foul-smelling spathe in spring. The corm is edible only after thorough processing; raw tissue is acrid.

Mature size: Leaf to about 1.3 m tall and wide; corm can reach 20-25 cm across and several kilograms.

Watch for — Corm rot in dormancy: Caused by moisture and cold while dormant. Keep the lifted or potted corm dry and above 10°C through winter.

How to tell konjac needs repotting

Repotting on a calendar is less reliable than reading the plant. For konjac, 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 konjac 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 konjac

Lift and divide every 3–4 years once clumps congest. Rather than a true repot, konjac is lifted and divided once the clump congests and flowering drops off. Tuberous perennial aroid producing one large, deeply divided umbrella-like leaf per season from an underground corm, with a malodorous inflorescence before leaf in spring..

What size pot to step konjac up to

Pot size matters less than depth and spacing here. When you replant konjac, 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 konjac

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 konjac in full growth or flower sets it back badly.

Step-by-step: repotting konjac

Wait for dormancy. Let konjac 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 rich, free-draining humus soil 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 konjac, 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 konjac

Konjac wants rich, free-draining humus soil. Plant in fertile, loose, well-drained soil high in organic matter. In pots use a free-draining mix with added compost and grit. Waterlogging during dormancy rots the corm, so drainage is critical. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting konjac — frequently asked questions

How often should you repot konjac?

Lift and divide every 3–4 years once clumps congest for konjac. Konjac 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 rich, free-draining humus soil. Crowding, not pot size, is what reduces flowering over time.

What size pot does konjac need?

When is the best time of year to repot konjac?

Do you "repot" konjac, or lift and divide it?

You lift and divide it. Konjac 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 konjac after repotting?

Hold off feeding konjac 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.