Repotting guide

When & how to repot Choy Sum 'Sumo' (Brassica rapa var. parachinensis 'Sumo')

Also called Sumo choy sum, flowering pak choi.

More about choy sum 'sumo'

About Choy Sum 'Sumo'

Brassica rapa var. parachinensis 'Sumo' · also called Sumo choy sum, flowering pak choi · edible

Choy Sum 'Sumo' is a vigorous, large-framed flowering choy sum producing thick, succulent stems, broad leaves, and yellow buds for stir-fries. Bred for heavier yields and good heat tolerance, it matures in around 40-55 days and regrows side shoots after cutting, making it a productive cool- and warm-season Asian green.

Mature size: 35-50 cm tall and 25-35 cm wide.

Watch for — Bolting under stress: Heat, dryness, or root disturbance trigger fast flowering and bitter stems. Keep well watered, sow in suitable seasons, and cut stems young.

How to tell choy sum 'sumo' needs repotting

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

Roots growing out of the drainage holes, or the rootball lifting the plant proud of the rim.
Soil that has shrunk away from the pot sides and no longer holds water.
The pot is unstable because the plant has grown top-heavy.
Old, compacted, broken-down mix that stays wet too long — for a succulent that is a rot risk, so refresh it even if the pot size is fine.

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 choy sum 'sumo'

Every 2–3 years, into bone-dry mix. Choy Sum 'Sumo''s growth habit — large, upright, branching plant with a stout central flowering stem and substantial leaves; resprouts vigorous side shoots after the main harvest. — sets the pace. Choy Sum 'Sumo' is a vigorous, large-framed flowering choy sum producing thick, succulent stems, broad leaves, and yellow buds for stir-fries. Bred for heavier yields and good heat tolerance, it matures in around 40-55 days and regrows side shoots after cutting, making it a productive cool- and warm-season Asian green.

What size pot to step choy sum 'sumo' up to

Use a pot only one size up — or even the same pot with fresh gritty mix if the roots have room. Choy Sum 'Sumo' stores water and rots in a large pot of slow-drying soil. A tight terracotta pot that dries fast is far safer than a generous plastic one. Never up-pot a succulent by several sizes.

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 choy sum 'sumo'

Spring or summer, while choy sum 'sumo' is in active growth and warm, is best — roots recover fastest then, and the plant is not sitting in cool damp soil. Avoid repotting a succulent in winter dormancy.

Step-by-step: repotting choy sum 'sumo'

Repot dry. Do not water choy sum 'sumo' for several days first. Working with dry roots and dry mix dramatically lowers the rot risk for a succulent.
Pick a snug, fast-draining pot. Choose terracotta one size up at most, with a drainage hole. Have gritty deep, fertile, well-drained loam ready.
Tip it out and clean the roots. Slide the plant out, crumble off the old soil, and trim any black, mushy or dead roots with clean snips.
Pot into dry mix. Set choy sum 'sumo' at its original depth in dry gritty mix, firming gently. Do not bury the stem deeper than it was.
Wait a week before watering. Leave it completely dry and out of harsh sun for about 7 days so any damaged roots callus. Only then water lightly.

Aftercare

Keep choy sum 'sumo' completely dry and out of fierce sun for about a week so any nicked roots callus before they meet moisture; watering a freshly repotted succulent is the classic way to rot it. Then resume the normal lean, dry rhythm. Do not fertilise for about 3 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for choy sum 'sumo'

Choy Sum 'Sumo' wants deep, fertile, well-drained loam. Rich soil with abundant organic matter, pH 6.0-7.5; this larger cultivar appreciates extra fertility. Keep near-neutral pH to suppress clubroot. Use deep containers if not in beds. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting choy sum 'sumo' — frequently asked questions

How often should you repot choy sum 'sumo'?

Every 2–3 years, into bone-dry mix for choy sum 'sumo'. Repot choy sum 'sumo' every 2–3 years into a snug pot of deep, fertile, well-drained loam, ideally in spring or summer. Let it sit in dry soil and do not water for about a week afterwards so any nicked roots can callus. Over-potting and watering straight away is what rots succulents.

What size pot does choy sum 'sumo' need?

When is the best time of year to repot choy sum 'sumo'?

Should you water choy sum 'sumo' after repotting?

No — not straight away. Repot choy sum 'sumo' into dry mix and wait about a week before the first watering so any damaged roots callus over. Watering a freshly repotted succulent is the single most common way to rot one.

Should you fertilise choy sum 'sumo' after repotting?

Not immediately. Wait about 3 weeks after repotting choy sum 'sumo'. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.