Repotting guide

When & how to repot Komatsuna 'Torasan' (Brassica rapa var. perviridis 'Torasan')

Also called Torasan komatsuna, Japanese mustard spinach.

More about komatsuna 'torasan'

About Komatsuna 'Torasan'

Brassica rapa var. perviridis 'Torasan' · also called Torasan komatsuna, Japanese mustard spinach · edible

Komatsuna 'Torasan' is a fast, bolt-tolerant Japanese mustard spinach grown for tender, mild glossy leaves harvested in 35-45 days. It thrives in cool weather, tolerates light frost, and crops as cut-and-come-again or full heads. Vigorous and forgiving, it suits raised beds, containers, and successional sowing across spring and autumn.

Mature size: Leaves 25-30 cm tall; full plants reach 30-45 cm if left to mature.

Watch for — Clubroot: Soil-borne brassica disease causing swollen, distorted roots and wilting. Lime to near-neutral pH, rotate beds, and avoid waterlogging.

How to tell komatsuna 'torasan' needs repotting

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

Roots circling the bottom of the module or pot, or poking out of the drainage holes.
The seedling dries out within a day and growth has visibly stalled.
Roots are white and matted in a tight spiral when you tip the plant out.
It has outgrown its current container for the stage of the season — pot komatsuna 'torasan' on before it becomes hard root-bound.

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 komatsuna 'torasan'

Pot on seedlings as they grow; not a perennial repot. Komatsuna 'Torasan'is grown for one season, so the question is really “how often to pot on” — keep moving it up before the roots circle. Upright rosette of broad, glossy oval leaves on slender stalks; quick-growing and re-sprouting after cut-and-come-again harvests until it bolts..

What size pot to step komatsuna 'torasan' up to

Pot komatsuna 'torasan' on gradually — a seedling jumped straight into a huge pot sits in cold, wet, airless soil and stalls. Step up one or two sizes at a time as the roots fill each container, finishing in a large final pot or the ground. The aim is roots that never circle and never check.

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 komatsuna 'torasan'

Pot komatsuna 'torasan' on through the active growing season, whenever roots fill the current container — there is no single date, just "before it becomes root-bound". Avoid potting on during a cold snap.

Step-by-step: repotting komatsuna 'torasan'

Pot on before it is root-bound. Check komatsuna 'torasan' regularly; move it up as soon as roots reach the edge of the cell or pot, not after they have circled.
Step up one or two sizes. Choose the next container up — not a giant one. Cold, wet, unused soil around a small root system stalls seedlings.
Knock it out gently. Support the stem, tip the pot, and ease the rootball out without breaking it. A little teasing of circled roots at the base is fine.
Pot into rich mix. Set it into fresh rich, moisture-retentive loam at the same depth (tomatoes are the exception — they can go deeper to root along the stem).
Water in and grow on. Water well, keep it in good light, and resume feeding once it is established and growing again.

Aftercare

Water komatsuna 'torasan' in well and keep it in bright light; a freshly potted-on seedling can wilt for a day while roots settle, so do not overcompensate by drowning it. Do not fertilise for about 1 week — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for komatsuna 'torasan'

Komatsuna 'Torasan' wants rich, moisture-retentive loam. Fertile, well-drained soil high in organic matter, pH 6.0-7.5. Lime acidic soils toward neutral to suppress clubroot. Works well in deep containers with quality potting mix. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting komatsuna 'torasan' — frequently asked questions

How often should you repot komatsuna 'torasan'?

Pot on seedlings as they grow; not a perennial repot for komatsuna 'torasan'. Komatsuna 'Torasan' is a seasonal crop, so you pot it on as a growing plant rather than repotting a perennial. Step seedlings up gradually into rich, moisture-retentive loam so the roots never circle the cell, ending in a large final container. A root-bound transplant stalls and never fully recovers.

What size pot does komatsuna 'torasan' need?

When is the best time of year to repot komatsuna 'torasan'?

Can you put komatsuna 'torasan' straight into a much bigger pot?

No. Even a fast-growing komatsuna 'torasan' should only go up one pot size at a time. A vastly oversized pot holds a reservoir of wet soil the roots cannot reach, which stays cold and soggy and rots the roots — the opposite of what you wanted.

Should you fertilise komatsuna 'torasan' after repotting?

Not immediately. Wait about 1 week after repotting komatsuna 'torasan'. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.