Figure 1: A bunch of white-stemmed pak choy (buk choy) (left) and a young green stemmed Shanghai pak choy plant.
Pak choy (pak choi) (Brassica rapa var chinensis) is an extremely versatile plant that is consumed boiled, sauteed, steamed, braised, stir-fried and in salads.
Within the market, it is known by various names, including:
- Chinese chard
- Chinese celery cabbage
- Chinese white cabbage
- buk choy
- bok choy
- pak tsoi
Classical pak choy is a loose head of up to a dozen glossy, green leaves with smooth margins.
Four major types of pak choy have been identified based on appearance - Chinese white-stemmed, soup-spoon type, green-stemmed (Shanghai) and squat Canton type. The white-stemmed varieties (often sold as buk choy in Queensland) and the green-stemmed varieties are the most popular (see Figure 1). The white-stemmed variety is sturdy, with light to dark green leaves often curling outwards. Its leaf stalks are white, wide, shortish and generally flat, sometimes overlapping at the base of the plant. White-stemmed pak choy tends to grow to approximately 30 cm high and is most often used in Asian stir-fries.
The green-stemmed variety has light green stalks that are broad and flattish, and wide at the base. Leaves tend to be more rounded, a lighter green and smoother than the white-stemmed varieties. Generally, they are harvested when only 15 cm tall, mostly for use in salads, though commonly also for stir-fries.
Climate and soils
Pak choy is a cool season crop that prefers moist and uniform conditions in full sunlight. High temperatures with long days will induce bolting, especially in the white-stemmed varieties. The ideal temperature during growth is 15-20°C and, while best grown in spring and autumn, it can be grown all year round. Most varieties of pak choy can tolerate light frosts. The green-stemmed varieties are hardier than the other varieties in both heat and cold.
Pak choy should also be grown where they have some protection from the wind, as the young plants can bruise easily in windy conditions. Pak choy prefers rich, loamy soils with high fertility, organic matter and water retention. The ideal soil pH is 6.5-7.0, and pak choy is sensitive to acid conditions below pH 6.0. If the soil pH is below 6.0, apply agricultural lime at least four weeks before sowing.
Pak choy seeds are extremely small and, therefore, difficult to handle when sowing. Either sow pak choy directly into the row and thin to an appropriate spacing, or transplant 15-30 days after seeding, depending on the variety. Transplanting may reduce bolting, especially during summer. The soil should be well prepared so that the beds are raised with good drainage and air circulation.
Within-row spacing is 2.5-10 cm for the smallest varieties and up to 45 cm for the largest. Spacing between rows is 15-30 cm. Do not sow seeds deeper than 2 cm below the surface.
Pak choy is a shallow-rooted crop and requires frequent watering. Apply light irrigations to avoid leaching. Protect outdoor plants with film covers in winter and shading net in summer. Do not apply large amounts of nitrogen to soil, as it may increase the incidence of bacterial soft rots in pak choy.
Pests and diseases
The most common problems affecting pak choy are clubroot, downy mildew, white rust, aphids, caterpillars and snails/slugs. You can manage them using registered pesticides, fungicides or insecticides. You can also control weeds with a registered herbicide or inter-row cultivation, but avoid working too deep as pak choy has a shallow root system. Good soil aeration helps control bacterial soft rots, especially in summer. You may reduce the incidence and severity of clubroot if you apply agricultural lime at least four weeks before sowing.
Harvesting, storing and marketing
Pak choy is usually harvested by hand, cut at the base 35-55 days after sowing. Always pick pak choy when leaves are fresh and crisp, and before the outer leaves turn yellow. Remove any dead or damaged leaves, trim the base flush with the first petiole and wash the plant. Harvest during a cooler part of the day. Yields are usually about 15 t/ha. Market prices are highest for green, turgid produce.
Pak choy is usually sold in bunches of 3-5 plants held by string or rubber bands, though you must take care as plants bruise easily. They usually sell for $0.50-3.00 per bunch. Whole plants or separated leaves may also be packaged in modified atmosphere plastic bags. The green-stemmed variety is often sold wholesale for use in bags of salad mix. Pak choy is extremely susceptible to wilting. However, at 1°C and relative humidity greater than 85 per cent, white-stemmed pak choy can be stored for 7-14 days and the green-stemmed pak choy for 12-20 days. Modified atmosphere packaging can increase shelf life even further.
- Larkcom, J 1991, Oriental vegetables, John Murray (Publishers) Ltd, London.