Water spinach: growing, harvesting & benefits

Water spinach is a versatile plant that offers a refreshing change from lettuce and spinach. This leafy vegetable is very popular in Asian cuisines.

Water spinach (Ipomoea aquatica) did not get its name by chance: it is grown in very humid, often wet conditions. As delicious as it is, achieving a good yield from a UK garden takes some dedication. For die-hard lovers of Asian cuisine, it may be worth the effort, as freshly grown water spinach is hard to come by in Europe. Read on to find out all about this beloved Asian leafy vegetable, including step-by-step instructions on how to successfully grow water spinach.

Water spinach: origin and properties

Like the sweet potato, water spinach belongs to the genus Ipomoea and the family Convolvulaceae. The vegetable has a few different names depending on the country, such as phak bung in Thailand and kangkong in Indonesia. As the aquatica part of its scientific name indicates, water spinach is found growing in streams, ponds, rivers and flooded rice fields in its native habitat. Its range spans the tropical and subtropical zones. Nowadays, it can be found in many different regions. In our latitudes, however, water spinach can only thrive under artificial conditions such as in a greenhouse − it is simply too cold outdoors. In warm climates, the plant is perennial. However, as Ipomoea aquatica is not hardy, its life span is limited to 1 year in locations with colder temperatures. In both cases, the vegetable usually flowers between June and early autumn.

The marsh plant has thick, hollow stems on which the leaves grow in an alternating pattern. Water spinach leaves can be ovate to lanceolate, and the leaf stalk is arrow- or heart-shaped that tapers at the end of the leaf. All water spinach varieties can be divided into two types depending on their leaf shape and site requirements:

• Green stem water spinach (Ching Quat): narrow, pointed leaves; adapted to moist, wet soil; can thrive in the garden if it is kept constantly wet; bears white flowers
• White stem water spinach (Pak Quat): grows in an aquatic environment; broad leaves; bears pink flowers

The white to pale purple flowers are bee-friendly and attract butterflies. Water spinach’s trumpet-shaped flowers are also characteristic of many other Convolvulaceae, such as hedge bindweed (Calystegia sepium). Its capsule fruits are ovoid, brown, 7 to 10cm long and contain dark brown seeds. Whether creeping or floating, water spinach plants are fast-growing and can grow up to 3m long.

How to grow water spinach

Depending on the variety, water spinach is grown in water or soil.

Water spinach seeds can be sown indoors on a windowsill or in a greenhouse all year round. However, if you plan to grow water spinach in the garden, it is best to start the seeds at the end of February to the beginning of March. It is vital the plant gets plenty of sun. Water spinach also needs to be kept warm and protected from wind. In the UK, these conditions are easiest to provide in a greenhouse. During the cooler months with less daylight, use a plant lamp in the greenhouse to make up the difference. For outdoor cultivation, be sure to use insulating boards made of wood or polystyrene to protect your water spinach against the cold. Use troughs as planters for hydroponics or raised beds for growing in soil.

As the name suggests, water spinach needs constantly moist roots. While this is not a problem for water spinach grown hydroponically, it is essential to always keep the soil of water spinach growing in soil moist. Additionally, water spinach seeds need temperatures between 16 and 18 °C to germinate. For water spinach types that need to be grown in soil, soak the seeds overnight in clear water before sowing them 1cm deep in the soil.

Water spinach needs a soil high in nutrients. Our peat-free Plantura Organic Enriched Compost can be used both for starting seeds and later in the garden bed. Our pre-fertilised compost ensures a good supply of nutrients and offers Ipomoea aquatica optimal development conditions with its neutral pH value. Keep in mind, as our compost is peat-free (for environment’s sake) it stores somewhat less water, so you will need to water the water spinach somewhat more frequently. In May, the plants can be planted outdoors in a sunny spot. We recommend planting your water spinach in a container or raised bed. This makes it easier to ensure and regulate the moisture levels.

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In hydroponics, the cultivation takes place in water. To get started, you will need a wire mesh that stretches over your chosen, water-tight container. It is important that the holes in the mesh are very small. You can either place the seeds on the mesh immediately, provided they do not fall through, or use pre-grown seedlings with well-formed roots. Simply place the young plants on the wire − the roots will find their way down to the water, ensuring the plants stand upright.

As an alternative to wire netting, you can grow your water spinach on clay pebbles. Get a container with drainage holes, set it on a plant saucer, and fill it with already expanded clay pebbles. Plant the water spinach seedlings in the clay pebbles and fill the planter partway with water.

The right care

It is important that the water spinach plants are always kept moist or wet. Also, water spinach grows and branches out from its base leaves, so if you wish to have multiple harvests, be sure not to cut off the base leaves when harvesting or pruning your water spinach.

For a rich harvest, fertilise water spinach regularly. Hydroponics require a special fertiliser − soil fertilisers are not suitable here. When growing water spinach in soil, we recommend an organic, nitrogen-rich, liquid fertiliser such as our Plantura Liquid Flower Food. Not only does it stimulate water spinach’s leaf and shoot growth and protect against overfertilisation, but it is also easy to apply when watering. Apply liquid fertiliser every 2 weeks. Between applications of fertiliser, water with clear water only.

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Do not forget: change the water in hydroponics regularly to inhibit the development of harmful germs and bacteria.

If you would like to overwinter your water spinach, be sure to grow your plants in a container you can easily move. Cut back the water spinach plants and place them indoors or in a greenhouse. It is important that their overwintering location is bright and warm. A temperature of around 20 °C and consistent watering are ideal. Only harvest or fertilise water spinach in winter if the heating and additional lighting are proving to provide good growing conditions. The containers can be put outside again from mid-May onwards, after the last frosts.

If you only have room to overwinter one water spinach plant, do not despair. In spring, simply take cuttings from it to grow more plants.

Harvesting and preparing water spinach

Under optimal conditions, you can harvest water spinach after 4 to 6 weeks. However, in most cases, it takes a bit longer. Apart from the base leaves, everything can be cut off. Radical pruning encourages the plant to sprout and branch. When the side shoots reach a length of about 15cm, the next pruning can take place.

Water spinach recipes: from the tender stalk to the leaves, every part of the water spinach plant can be used. That said, removing older stems prevents the vegetable from becoming bitter. In Asian cuisine, the mild-tasting water spinach is used in salads and wok recipes. Simply fry the water spinach briefly in oil, and serve it with chilli, garlic and/or other sauces. It also pairs well with other vegetables such as onions, tomatoes and mushrooms. Just like spinach, water spinach can also be boiled. In addition, water spinach is often combined with tofu.

Is water spinach healthy?

Water spinach is very low in calories and consists of 90% water. Despite the high water content, this vegetable is nutritious: its dry matter contains about 24% protein and 48% carbohydrates. In contrast to white sugar, the human body breaks down and absorbs these longer, complex carbohydrate chains slowly. This means that, after consumption, the body’s blood sugar levels remain relatively constant. Subsequently, including more vegetables like water spinach into your diet should help to counteract diseases like diabetes. Lastly, water spinach also contains vitamins C and A − both are beneficial antioxidants that help the body stay healthy.