Mustard cabbages do well on fertile, well-drained soils with a good moisture-holding capacity. If drainage is poor, seeds should be planted on raised beds. The pH should be between 5.5 and 7.0, and the soil should be free of nematodes. If nematodes are present, fumigate the: soil before planting. Add lime if the soil is very acid. Add organic matter to improve the structure and water-holding capacity.
Apply general garden fertilizer, such as 10-30-10, at a rate of about 3 pounds per 100 square feet. Apply one-half at seeding time and the other half at thinning, about 3 to 4 weeks after planting. Place fertilizer in a band about 3 to 4 inches away from the base of the plants. Over-fertilization will result in plants that are too succulent and that may develop tipburn under warm conditions.
Planting and Thinning
Plant seeds directly in the field in rows spaced about 12 to 15 inches apart. At 3 to 4 weeks of age, before the plants start to become crowded, thin to about 10 to 12 inches in the rows for kai choy and 8 to 10 inches for pak choy. If thinning is delayed too long, the plants will become spindly and leggy, and may bolt before forming a useful plant.