Fertilising guide

How to fertilise Choy Sum 'Sumo' (Brassica rapa var. parachinensis 'Sumo')— schedule & NPK

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.

Growth habit: Large, upright, branching plant with a stout central flowering stem and substantial leaves; resprouts vigorous side shoots after the main harvest.

Watch for — Flea beetles: Riddle seedling leaves with tiny holes, weakening young plants. Use fine mesh from sowing and feed for quick growth.

What fertiliser choy sum 'sumo' actually wants — and why

Choy Sum 'Sumo' feeds in two distinct phases — balanced to build the plant, then high-potassium the moment flowering starts to set and fill a heavy crop.

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 choy sum 'sumo': 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 choy sum 'sumo', 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 choy sum 'sumo':

A heavy feeder given its size: enrich soil with compost or balanced fertiliser before planting and apply nitrogen-rich liquid feed every 1-2 weeks during rapid growth for thick, tender stems. So: a balanced feed or compost at planting, then a high-potash liquid every 1-2 weeks from first flower through harvest across the main season (spring through early autumn).

The dormant-season rule matters more than the exact interval: skip feeding entirely when choy sum 'sumo' 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 choy sum 'sumo'

Follow the crop-feed label rate for choy sum 'sumo' — these are calibrated for hungry vegetables. Consistency through fruiting matters more than strength; erratic feeding causes problems like blossom-end rot.

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

Signs you are over-feeding choy sum 'sumo'

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

Vigorous dark-green leafy growth but few flowers or fruit (excess nitrogen).
Lush foliage hiding the crop; soft growth prone to pests and disease.
Salt crust on the soil and scorched leaf edges in containers.

Signs you are under-feeding choy sum 'sumo'

Pale, yellowing lower leaves and stunted growth.
Small fruit, poor set, and a quickly exhausted plant.
Blossom-end rot and weak cropping from erratic or insufficient feeding.

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

Flushing and leaching the salts

In containers, fertiliser salts build up fast — water choy sum 'sumo' thoroughly so excess drains from the base each time, and flush pots with plain water every few weeks to prevent a damaging salt build-up.

Organic vs synthetic feeds for choy sum 'sumo'

Organic options

Garden compost or well-rotted manure dug in before planting, plus a liquid comfrey or seaweed feed once fruiting starts. UK: comfrey feed or organic Tomorite; US: Espoma Tomato-tone or Neptune's Harvest. Builds soil and feeds in one.

Synthetic / liquid feeds

A balanced feed at planting then a high-potash tomato feed in fruiting — UK: Growmore at planting then Tomorite (Levington) or Phostrogen; US: a balanced 10-10-10 then Miracle-Gro Tomato or a bloom booster.

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 choy sum 'sumo' — frequently asked questions

What fertiliser does choy sum 'sumo' need?

Balanced (even N-P-K) at planting for roots and frame, then switch to a high-potassium ("high-potash") tomato-style feed once the first flowers open — potassium is what sizes and ripens fruit, not nitrogen. Choy Sum 'Sumo' feeds in two distinct phases — balanced to build the plant, then high-potassium the moment flowering starts to set and fill a heavy crop.

How often should I feed choy sum 'sumo'?

A heavy feeder given its size: enrich soil with compost or balanced fertiliser before planting and apply nitrogen-rich liquid feed every 1-2 weeks during rapid growth for thick, tender stems. A heavy feeder given its size: enrich soil with compost or balanced fertiliser before planting and apply nitrogen-rich liquid feed every 1-2 weeks during rapid growth for thick, tender stems. So: a balanced feed or compost at planting, then a high-potash liquid every 1-2 weeks from first flower through harvest across the main season (spring through early autumn).

What strength of feed for choy sum 'sumo'?

What does over-feeding choy sum 'sumo' look like?

Vigorous dark-green leafy growth but few flowers or fruit (excess nitrogen). Lush foliage hiding the crop; soft growth prone to pests and disease. Salt crust on the soil and scorched leaf edges in containers. Staying on a high-nitrogen feed once choy sum 'sumo' starts flowering is the classic error — you get a huge leafy plant and a disappointing crop. Switch to high-potash the moment flowers appear.

Should I flush the soil of choy sum 'sumo'?