Mature size & growth rate

How big does Purple Choy Sum (Brassica rapa var. parachinensis 'Purple') get?

Also called purple choy sum, purple Chinese flowering cabbage.

More about purple choy sum

About Purple Choy Sum

Brassica rapa var. parachinensis 'Purple' · also called purple choy sum, purple Chinese flowering cabbage · edible

Purple Choy Sum is an ornamental-yet-edible flowering cabbage with striking purple stems and leaf veins, topped by yellow buds. Grown for sweet, tender stems and shoots, it matures in about 40-55 days, holds colour best in cool weather, and crops cut-and-come-again, adding vivid colour to beds and stir-fries alike.

Mature size: 30-45 cm tall and 20-30 cm wide.

Indoor size vs how big it gets in the wild

Purple Choy Sum reaches its full size within one growing season — there is no "long-term" size, just how big it gets before you harvest or it dies back. Indoors and in a pot, expect 30-45 cm tall and 20-30 cm wide.. A pot, your light levels and a little pruning are what set the final size in a home, far more than the plant's theoretical potential.

It sizes up fast and once, racing from seedling to full size in a single season; after cropping it is finished, so size is a within-season question.

Growth rate and years to mature

Purple Choy Sum is a fast grower. Realistically, expect a single growing season — it reaches full size in one year, then is done. Its feeding profile backs this up: feed as a leafy/stem crop: incorporate compost or balanced fertiliser at planting, then apply nitrogen-rich liquid feed every 2 weeks; cool-season feeding combined with bright light supports the strongest purple colour.

Want this turned into the right next pot at the right moment? The pot size calculator and the purple choy sum repotting guide cover when and how much to size up — pot size is one of the biggest levers on how fast purple choy sum grows.

How to keep purple choy sum smaller

You are not stuck with the maximum size. For purple choy sum specifically, these are the levers, in order of impact:

Choose a compact or dwarf variety of purple choy sum from the start — that is the most reliable size control for an annual.
Grow it in a smaller container to naturally limit how large it gets.
For some crops, pinching or pruning the growing tips keeps the plant shorter and bushier.
Sow a little later or space plants closer if you specifically want smaller individual plants.

How to grow purple choy sum bigger or faster

If you want it to fill the space sooner, push the conditions rather than hoping — for purple choy sum the accelerators are:

Full sun, warm soil and steady water are what drive a crop to full size fastest.
Sow at the right time for your zone so it gets the whole season to size up.
Feed appropriately for the crop and never let it check (stall) from drought or cold.

Light is almost always the ceiling. The purple choy sum light requirements page covers exactly how bright a spot it needs to grow at its potential instead of stalling.

When purple choy sum outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for purple choy sum:

It sprawls beyond its bed or container before harvest — usually a spacing or support issue.
It flops or needs staking once it hits full height.
Once it has fruited or bolted, it is at its final size for good — the next plant is a new sowing.

If it is the pot rather than the room, it is a repotting job, not a goodbye — see the purple choy sum repotting guide. If you want more of this plant instead of a bigger one, the purple choy sum propagation guide turns prunings into new plants.

Purple Choy Sum size — frequently asked questions

How big does purple choy sum get?

Purple Choy Sum reaches 30-45 cm tall and 20-30 cm wide. when grown indoors. It sizes up fast and once, racing from seedling to full size in a single season; after cropping it is finished, so size is a within-season question.

Is purple choy sum slow or fast growing?

Purple Choy Sum is a fast grower. Expect a single growing season — it reaches full size in one year, then is done. Purple Choy Sum reaches its full size within one growing season — there is no "long-term" size, just how big it gets before you harvest or it dies back.

How long does purple choy sum take to reach full size?

Roughly a single growing season — it reaches full size in one year, then is done. Light, pot size and feeding move that timeline more than anything else.

How do I keep purple choy sum smaller?

Choose a compact or dwarf variety of purple choy sum from the start — that is the most reliable size control for an annual. Grow it in a smaller container to naturally limit how large it gets. For some crops, pinching or pruning the growing tips keeps the plant shorter and bushier. Sow a little later or space plants closer if you specifically want smaller individual plants.

How can I make purple choy sum grow bigger or faster?

Full sun, warm soil and steady water are what drive a crop to full size fastest. Sow at the right time for your zone so it gets the whole season to size up. Feed appropriately for the crop and never let it check (stall) from drought or cold.