How to Prune Chinese mustard?
No pruning required

Chinese mustard · Brassica juncea
Also known as: Dijon mustard; gai choi; Indian mustard; kai choy; kai tsoi; karashina; leaf mustard; mibuna; mustard cabbage; mustard greens; rai; Swatow mustard
Sow seed outdoors in deep, fertile but firm, soil that isn't too acidic. If space is limited, start the seeds in modules or seedtrays and plant outside when big enough to handle easily (about 5 or 6 leaves). Watering through the summer months is very important. For more advice see vegetable cultivation
No pruning required