Water Spinach (Kangkong)
Note Number: AG0900
Published: March 2002
Updated: August 2010
Water spinach (Ipomea aquatica) is of East Indian origin and a member of the Convolvulaceae (morning glory) family. It has long, jointed and hollow stems, which allow the vines to float on water or creep across muddy ground. Adventitious roots are formed at nodes which are in contact with water or moist soil. They exude a milky juice, and are white or green, depending on variety. Water spinach has no relationship with common spinach, but is closely related to sweet potato (Ipomea batatas).
Water spinach is an herbaceous aquatic or semi-aquatic perennial plant of the tropics or subtropics. Leaves are flat, and vary in shape depending on variety, from heart-shaped to long, narrow and arrow-shaped. Narrow leaves are 1-2.5 cm wide and 20-30 cm long. Broad leaves are up to 5 cm wide and 15-25 cm long.
The large, attractive flowers have the typical open, trumpet shape of convolvulus or bindweed flowers. They are usually white, sometimes with a pinkish centre. Wild forms may have purple or mauve flowers.
The leaves have a very pleasant, mild, sweet flavour and a slightly slippery texture, which contrast when cooked with the crispness of the stems. The Chinese consider the white-stemmed forms better flavoured and tenderer than the green. Like many other leafy vegetables, water spinach's leaves are very nutritious, being rich in vitamins and minerals. They are also a mild laxative.
There are two major cultivars of water spinach,
- Ching Quat (known as "green stem") – this has a narrow, pointed leaves and white flowers and is adapted for moist soils. This can be grown in beds, provided there is always plenty of moisture.
- Pak Quat (known as "white stem") – this has broad, arrow-shaped leaves and pink flowers. It is adapted to aquatic conditions and also called "Water Ipomea".
Water spinach has different names according to language and dialect. Water convolvulus, Kang cong and Swamp cabbage are some alternative names in English. It is known in Mandarin as kong xin cai (empty heart/stem vegetable); ong tsoi and weng cai (pitcher vegetable) in Cantonese, kang kong in Filipino and Malasian and in Japanese as Asagaona (morning glory leaf vegetable).
Practically all parts of the young plant are edible, although the shoot tips and younger leaves are preferred. Water spinach is consumed differently in Western and Chinese cuisines. Water spinach deteriorates rapidly once picked, so must always be used very fresh. The leaves can be used whole, or cut into smaller pieces. Like ordinary spinach, the stems require slightly longer cooking than the leaves.
The Cantonese exclusively stir-fry it.
Coarse stems and leaves are often used for animal fodder.
Water spinach is not adapted to climates with mean temperatures below 10 °C and the optimal temperature is around 20C – 30C. It is grown year-round in the tropics. Flowering occurs under short-day conditions and commences from mid-summer onwards. Water spinach is perennial in warm climates, but an annual under cooler growing conditions. It tolerates very high rainfall, but not frost.
Water spinach can be grown outside in summer. In cool areas, it can be grown in unheated greenhouses in summer, but will require heated greenhouses for a spring crop. It prefers full sun but where summer temperatures are very high, it is sometimes grown as a ground cover beneath climbing plants. Water spinach should be sheltered from strong winds.
Soil and soil preparation
Water spinach requires fertile soils rich in organic matter. Overwatering can leached out readily available nutrients and will affect yield. Therefore slow releasing fertilizers are recommended to avoid the loss of nutrients. The most suitable soil pH ranges from 5.5 to 7.0.
Sowing and planting
In moist soil culture, the crop is grown on raised beds 60-100 cm wide. Seeds are sown directly or nursery-grown seedlings are transplanted into the beds. Seed should be no more than 2 years old and can be soaked for 24 hours before sowing to encourage germination. Soil temperature requirement for germination is 20 °C.
When rainfall is low, frequent heavy irrigations are necessary for high quality shoots.
To produce strong seedlings, seed should be sown 5-10 mm deep in trays with potting mix deep enough to allow the plants to develop a good root system. Transplanting should take place when plants are 10-15 cm high, with four true leaves. Highest yields are obtained by spacing plants at 15x15 cm. They can also be grown in rows about 30 cm apart with plants at 20 cm spacing within rows.
Propagation from cuttings
Water spinach can also be raised from stem cuttings, 30-40 cm long, taken from the young growth just below a node, and planted about 15 cm deep. To ensure earliness, growers in China sometimes lift roots at the end of the season, store them carefully in winter, and plant shoots from them in spring.
For aquatic culture, cuttings from the broadleaved cultivars are transplanted into puddled soil, similar to the planting of rice in paddies. The cuttings are about 30 cm long with seven to eight nodes, and are planted 15-20 cm deep and spaced 30-40 cm apart.
For aquatic culture after planting the land is flooded to 3-5 cm in depth and the water is kept flowing continuously. In moist soil culture, irrigation should take place every 1-2 days for high quality shoots if rainfall is low.
Before planting, the crop must be given sufficient nutrients to produce quality spinach. After the plants are established, nitrogen in the ammonium form should be applied at the rate of 40-50 kg/ha, then the water level is raised to 15-20 cm depth. Plants respond well to nitrogen, but over-feeding must be avoided because for high nitrate concentrations in the leaves and stems can result which is undesirable.
Regular applications of an organic liquid fertiliser should occur every 2 weeks or so for best results. Liquid fertilisers are usually diluted before application the plants.
Pests and diseases
The main fungal diseases, which effect water spinach, are stem rot (Fusarium oxysporum) and black rot (Ceratocystis fimbriata). For prevention of fungal diseases strategies such as use of clean land and rotate crops every third or fourth year, carefully select stems for propagation that are disease free
Internal cork, chlorotic leaf spot, yellow dwarf and russet crack are viral diseases which can also affect water spinach.
The most important insect pests are leaf beetle, aphids, and wire worm.
Water spinach should be harvested before it flowers. In the semi aquatic type, the crop is ready for harvest 50-60 days after sowing, when entire plants are pulled, washed and bundled. More than one harvest can be taken if shoots are cut above ground level, allowing secondary shoots to grow from nodes below the cut.
In the aquatic type, the first harvest can be made after about a month of good growth. The frequency of harvesting will depend on the growth rate of the crop. The upper part of the main shoot, about 30 cm long, is cut about 5 cm above water level. Bundles of 8-10 shoots are marketed. Removal of the main shoot stimulates horizontal shoot growth. These new shoots can be harvested in 4-6 weeks, depending on plant vigour and temperature. About 40 tonnes/ha can be harvested from three or more cuttings in a year.
Rapid and careful post-harvest handling is required to minimise damage to the fragile crop, especially due to wilting caused by moisture loss. To prevent this, the plants should be harvested during the coolest part of the day. After bunching, a fine spray of cold water should be applied, and the leaves kept in a cool place away from the wind.
Leaves are usually sold in 500 gram bunches in the markets.
Dahlen, M. (1992) A Cook's Guide to Chinese Vegetables, The Guide Book Company Ltd, Hong Kong.
Hackett, C. and Carolane, J. (1982) Edible Horticultural Crops. Academic Press, Australia.
Larkcom, J. (1991) Oriental Vegetables: The Complete Guide for the Gardening Cook. John Murray Ltd. London.
Nguyen, V. Q. (1992)Growing Asian Vegetable, Agfact H8.1.37, NSW Agriculture.
Rubatzky, V. (1990) Specialty and minor crops Handbook; Chinese Water Spinach, Swamp Cabbage, Kang Kong, Water Convolvulus. The small Farm Centre, University of California. USA.
Waters, C. T., Morgan, W.C. and Mc Geary, D.J. (1992) Oriental Vegetables: How to Identify, Grow and Use. Government of Victoria. Department of Agriculture, Agmedia, Melbourne.
Yamagushi, M. (1983) World Vegetables: Principles, Production, and Nutritive Values. AVI Publishing Company, USA.
Correct diagnosis is essential for effective pest and disease control. A commercial diagnostic service is available at the AgriBio Bundoora.
For further information, phone Crop Health Services on (03) 9032 7515.
For further information on registered chemicals, phone our Customer Services Centre on 136 186.
This Agriculture Note was prepared by Murat Top and Bill Ashcroft in March 2002.
It was reviewed by Neville Fernando and Rob Dimsey, Farm Services in August 2010.
Published and Authorised by:
Department of Environment and Primary Industries
1 Spring Street
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