Chinese Water Chestnuts

Most people only know Chinese Water chestnuts that have come out of a tin and don’t realise they can be grown in New Zealand. They are fun to grow. Botanically the Chinese water chestnut is a type of spike reed. The plant is rush like with upright tubular stems one to one and a half metres tall. It produces numerous corms which resemble gladioli. They need to be completely submerged with a controlled level of water for most of the life of the crop (similar to paddy rice) and it must be possible to drain the water for harvesting. So a trough or half barrel with a tap is ideal. We grow ours in an old concrete trough with tap.

The crop needs 210 frost free days for development. It is usually planted in spring and harvested in winter. They could be grown indoors in colder places.

In the trough I put a layer of manure mixed with old potting mix at the bottom and then soil or new potting mix on top to create a depth of approximately 40 cms. They prefer growing in full sun. If the corms are planted before they have sprouted the soil is periodically flooded and drained until the plants are about 20cm high. Once they are growing well the trough is flooded to a depth of about 10cms and I keep an eye on them over summer to keep that level of water and make sure they don’t dry out. It helps me to have the trough in a place where I walk by regularly and that is right next to a hose pipe as then I don’t forget about it!

The plants can grow to over a metre tall and, once the foliage has died back, can be used as a beautiful seed free mulch.

Water chestnuts starting to grow well in the Spring. Azolla weed on the surface of the water

Over the years people have written and asked about mosquito larvae and whether having this standing water around acted as a breeding place. I checked the trough and found there were a few so decided to ensure this wasn’t a factor by putting azolla pond weed on the surface of the water. Azolla is that floating pond weed that can be either green or red. It covers the surface of the water in between the plants preventing mosquitos from breeding there, is a nitrogen fixing plant too so helps feed the water chestnuts and also has the added advantage that, if the water level does reduce too much, they form a mulch on the growing medium and help stop it drying out. So adding azolla weed in is a good thing to do. I got mine from one of our ponds and only a very small amount is needed to get started as it multiplies rapidly.

Harvesting water chestnuts, azolla still visible on the soil surface

A well grown corm will be 30 – 45 mm in diameter and plants can yield between 2 and 5 kg each. After harvesting store wet in the fridge or store in cold water removing them to air dry about 1 – 2 weeks before use.

We usually eat our Chinese Water Chestnuts in stir fries where they add a moist, crunchy texture. We peel them and slice thinly. They can also be eaten raw, lightly boiled or grilled.

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