Pak choy
Commercial production

Department of Primary Industries and Fisheries, Queensland.

Figure 1. A bunch of white-stemmed pak choy (buk choy) (left) and a young green-stemmed Shanghai pak choy plant (right)

Pak choy (pak choi) (Brassica rapa var chinensis) is an extremely versatile plant which 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 and petsai. 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 (Figure 1). The white-stemmed variety is sturdy with light to dark green leaves often curling outwards and the 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-frys. The green-stemmed variety has light green stalks that are broad, flattish and widen 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, but are also commonly used in stir-frys.

Climate and soils

Pak choy is a cool season crop preferring 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 between 15 and 20°C and while best grown in spring and autumn, pak choy 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 to be grown on rich, loamy soils with high fertility, organic matter and water retention. The ideal soil pH is 6.5 to 7.0, 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.

Cultivation

choy seeds are extremely small, so difficult to handle when sowing. Pak choy can either be sown direct in the row and thinned to an appropriate spacing, or transplanted 15 to 30 days, depending on the variety, after seeding. 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 varies from 2.5 to 10 cm for the smallest varieties and up to 45 cm for the largest. Spacing between rows varies between 15 and 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. Outdoor plants can be protected by film covers in winter and shading net in summer. Do not apply large amounts of nitrogen to soil as this 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. They can be managed by using registered pesticides, fungicides or insecticides. Weeds may also be controlled by a registered herbicide or by inter-row cultivation, but avoid working too deep as pak choy has a shallow root system. Good airation of the soil is important as this helps to control bacterial soft rots especially in summer. Clubroot incidence and severity may be reduced if agricultural lime is applied at least four weeks before sowing.

Harvesting, storage and marketing

Pak choy are usually harvested by hand, cut off at the base 35 to 55 days after sowing. Pak choy should always be picked 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 tonne per hectare. Market prices are highest for green, turgid produce.

Pak choy is usually sold in bunches of 3 to 5 plants held by string or rubber bands (take care as plants bruise easily), and usually sells for $0.50 to  $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%, white-stemmed pak choy can be stored for 7 to 14 days and the green-stemmed pak choy for 12 to 20 days. Modified atmosphere packaging can increase shelf-life even further.

Additional information sources

• Recommended Reading: Larkcom, J. (1991) Oriental Vegetables. John Murray (Publishers) Ltd, London.

Further DPI&F information

• To access DPI&F's information and services, Queensland residents can contact the DPI&F Business Information Centre on 13 25 23 for the cost of a local call, from 8 am to 6 pm Monday to Friday (excluding public holidays). E-mail callweb@dpi.qld.gov.au. Non-Queensland residents phone (07) 3404 6999.

• Current national information on agricultural chemicals registered for use on all crops is available on the Infopest CD-ROM. Write to DPI&F, GPO Box 46, Brisbane, Qld 4001, E-mail infopest@dpi.qld.gov.au, visit the Infopest web page, or phone (07) 3239 3967 for further information.

Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries, Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.

Last reviewed 27 September 2007