Friday, 27 January 2017

Vietnamese coriander

Vietnamese coriander (Persicaria odorata) is an excellent perennial herb which should be more widely grown at home but is not easy enough to find.  It has a bunch of different common names including Vietnamese mint, laksa herb, hot mint, Cambodian mint, praew leaf, and many more.  It is not related to coriander at all, it is not related to the mint family, but it is eaten in Vietnam and is often used in laksa.
Vietnamese Coriander - growing as an emergent plant
I first saw this herb at a training day (I swapped it for some perennial leeks), the lady tore off a small cutting for me, then said something about it not surviving until I got home as it was the middle of summer and the course still had a few hours to go.  I put the little cutting in my pocket and when I got home it was bruised, limp and looked dead, so I put it in a cup of water in the shade.  It looked very dead to begin with but it grew roots within a few days and I have had it ever since.
Vietnamese Coriander rooted cutting
How to grow Vietnamese Coriander
I thought Vietnamese coriander was always grown as an emergent plant with its roots and stems under water and its leaves always sticking out of the water.  I have grown it this way for a few years and it has done rather well for me.  Recently I have seen it for sale with other terrestrial herbs, not sitting in a tray of water, but having a tag that says to water it well and not allow it to dry out at all.  I guess it is more versatile and hardy than I realised.

Honestly, I think growing it as an emergent is far more simple than trying to keep it well watered.  I grow this herb in the same way that I grow Chinese water chestnuts or duck potatoes or water cress, sometimes I even grow them together in the same bucket.  A bucket or something similar with soil a few inches from the top, filled with water is easy to set up and maintain, as is submerging a pot of soil in a bucket of water.  Each day when watering the rest of the vegetables you simply top up the water in the bucket.  If the water does dry off, the soil remains damp enough for your plant.  If there are mosquito issues either put in some small fish (research which ones to use first and always stay clear of Gambusia) or simply let it dry out once a week.  The soil needs to remain moist for this plant to flourish, but if there is no free water on top of the soil the mosquito larvae die or are eaten by ants pretty fast.  Doing this weekly will ensure that the mosquito do not have time to hatch, pupate and metamorphose into adults.  Not watering once a week is simple enough to do, or to not do as the case may be.

When growing in a bucket of soil and water the waterlogged soil tends to prevent any serious weed growth as few weeds can handle long periods of submerged roots.  The presence of open water tends to encourage frogs, superb fairy wrens and other tiny insectivorous animals which are beneficial for your garden.

Other than never letting this plant get dry, don’t let it run out of space or nutrients.  It will grow very fast, but if it runs out of space to grow or uses all the available nutrients it will stop growing completely.  The plant will not die, but if it is not growing then it is not supplying you with leaves so there is no point having it.  I have taken cuttings of this and put it in a glass of water, the cutting grows roots very fast, but then growth stops and it does nothing, absolutely nothing, for months.  This is because it needs nutrients, plant it in the soil and let it do its thing.  A similar thing happens when grown in a small pot of soil, it rapidly grows to fill the space it has been given, then it stops growing completely.  Cutting it back hard does not encourage a new flush of growth, only feeding it seems to make a difference.  This is as simple as tipping a little poultry manure into the bucket.

Vietnamese coriander does not like frost and very cold weather will significantly slow its growth.  As long as you keep a little of this plant out of the frost it will survive to regrow for you when the weather warms.  It is even possible to keep a cutting alive in a glass of water over winter if needed.  Try to keep in mind that in a glass of water this cutting will quickly look bad, stop growing, and the leaves may turn red and the leaves may go bitter, or the leaves may even drop off if it is too cold.  I know someone in Orange NSW who put bubble wrap over her plant to keep it alive over winter.  Any part that gets hit by frost will die off, but if any of the plant is alive it will regrow fast enough in warmer weather.
Vietnamese Coriander cutting starting to grow in water
Vietnamese Coriander growing in soil and water in a milk bottle
How to propagate Vietnamese coriander
I am told that Vietnamese coriander will not flower outside of the tropics due to daylight sensitivity issues as well as strict temperature/humidity requirements.  This is not the case at all.  I have had Vietnamese coriander flower for me and I have never lived in or anywhere near the tropics.  The flowers are small, uninteresting and white.

I don’t know if it needs a second clone for pollination due to self-incompatibility issues, or if the seeds need special conditions or mycorrhizae in order to grow, or if it can even produce viable seeds.  All I know is that it sometimes flowers for me but I have never obtained any Vietnamese coriander seeds.

Vietnamese Coriander Flowers
Vietnamese coriander is very easy to propagate from cuttings, one of the easiest I have ever grown.  Roots will grow quickly from any node that is under water, as long as at least one node is under water then it will grow roots.  Roots will only grow from a node, unlike herbs such as basil the roots will not grow from the stem.

I normally cut a section off the plant, remove the leaves from the lower few nodes, and then place it in water with the remaining leaves in the air and the leafless nodes under the water.  I normally remove leaves from several nodes as I am using them in my dinner, the parent plant you cut pieces off should regrow as long as you leave it with at least one node that has leaves.  If you do not remove the leaves from your cutting it will still grow roots quickly, but you run the risk that the leaves may possibly rot.

I have even seen Vietnamese coriander grown underwater in an aquarium once.  Short term this will work well and the plant will grow roots from every node, but I think that longer term this plant needs its leaves out of the water.  I really should experiment with this and see what it is capable of.  I would be hesitant to grow it using aquaponics in fear that it would take over and clog things pretty quickly.

Vietnamese Coriander Flowering
What does Vietnamese coriander taste like
I don’t know how to describe how things taste but I am rather fond of this one.  Some people say it smells much like coriander, some think it smells nothing like coriander, I think it does smell a bit like coriander.  Some people claim it smells like mint, I don’t see how anyone could ever think it smells even slightly minty and the word ‘mint’ in one of its common names probably refers to the aggressive growth.  Some say it is warm and peppery, others say citrusy, others disagree completely.  The internet says Vietnamese coriander has a  “lovely coriander taste with a clear citrus note; refreshing with a hot, biting, peppery after taste” which I think is a reasonably accurate description.

Vietnamese coriander is used in many dishes, as one of the common names suggests it is rather popular in laksa.  I like to put some leaves in my bowl and then pour in hot chicken soup.  The heat from the soup is enough to cook this herb and make it soft.  I think overcooking would make it lose much of its taste.  It goes well with chicken and I am told that it combines well with lime, chillies, garlic, ginger and lemon grass.

I don’t eat this herb raw myself as I find it slightly bitter, but have been told that it works well raw chopped into salads.  I really should try this one day and see if I like it.

Unlike coriander which some people love and others have a broken gene which makes it smell soapy to them, Vietnamese coriander does not appear to elicit the same extreme response from people.  That being said, this herb is not for everyone.  I really like the taste and smell of Vietnamese coriander, my wife dislikes it, some of my kids like it and the others are indifferent to it.
Vietnamese Coriander - more sunlight makes the purple more pronounced
Where to buy Vietnamese coriander in Australia
Some online places sell Vietnamese coriander, and some nurseries ocasionally stock it, but prices vary quite a lot and it is usually far more expensive than it should be.  The best thing about this plant is that it is perennial so you plant once and harvest forever.  I sell Vietnamese coriander plants or rooted cuttings, if it is available it can be found on my for sale page.
Vietnamese Coriander Rooting Cuttings ready to plant

2 comments:

  1. Great article, thanks. You've answered some questions I had. I grew it in water for years, and recently decided to put it beside my tap and water it every time I used the tap. In a barrel, not in the ground. It is enormous. I'll try eating it as you suggested. So far I hadn't used it at all. I like the idea of a couple of leaves in int bottom of a bowl of chicken soup. I'll try it in a salad, too. I like sharp-tasting leaves. Interesting the genetic thing about coriander.

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    1. Hi Parlance,

      I like Vietnamese coriander. It is a little bitter for me to enjoy it raw, but the bitterness goes away when cooked. Putting a few leaves in the bottom of a bowl of chicken soup makes it taste amazing.

      I believe it is a mutation to the OR6A2 gene that makes some people absolutely hate normal coriander. The broken OR6A2 gene incorrectly encodes an olfactory receptor making it overly sensitive to aldehydes. People with this broken gene often say coriander smells soapy or like stink bugs or dog vomit.

      I am quite lucky that I do not carry that mutation so regular coriander smells amazing to me!

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