Vietnamese cilantro/coriander, or Persicaria odorata is a very interesting plant that, like malabar spinach takes well to summer weather here more than the common cilantro that self seeds in my garden. Unlike my regular cilantro which bolts immediately when it hits 80+ degrees F it seems, Persicaria is fine with cool weather as well as heat.
I prefer to use regular cilantro when possible because it has a more delicate flavor whereas Persicaria to be honest nearly stinks with that cilantro flavor that some genetically prone people have so come to hate. (I wonder if they are the same volatile compounds as regular cilantro... if those regular cilantro haters would hate Persicaria... Pepsi challenge anyone?)
When the going gets tough though, I want me some cilantro flavor without bitter, tough stems and reach for the Persicaria.
This is a very easy plant to grow that prefers soaking wet soil (as it's technically a water plant), partial sun (despite what many sites seem to say) and good air circulation I find. It was tough growing this plant indoors, over the winter for me because of the immense need for water this plant needs, it promoted aphids and I eventually just had to toss the plant despite attempting to make cuttings from apparently non-affected plants. Cuttings, which I think didn't make it because of the poor winter light (no grow lights here).
If you have Asian grocery stores around, it should be relatively easy to find this herb sold in bunches for very cheap (89 cents here for a large bunch). It's very easy to propogate, just strip the bottom couple to few inches of leaves from their nodes and pop in a cup full of water until roots show (in about a few days) then plant in a relatively good wet location, or in a pot where you can move it around to a good location.
This year I have mine in a part sun/shade wet ditch-like area of my garden to see how it survives and also in a no-drainage container that's taller (this plant likes to trail) so I can keep the leaves relatively clean. I have no issues placing this plant/cuttings in a no drain container because it it a water hog and if past experience serves me right, it will take over the container quickly and need to be repotted soon anyways. So quickly it sucks up water from rampant growth that it will pot/root-bind itself and need water all the time it seems. So, if it looks like your Persicaria is drying out quickly and suffering, that's why.
You may encounter this herb as rau aum, laksa, smartweed, or Vietnamese mint. It also seems to go by the other Latin name of Polygonum odoratum.
Hardy to zones 11+, as I've said, you can overwinter it if you so choose to and have easy access to a cilantro-like flavor all w inter if you provide good conditions to avoid aphids. Like I said though, it's cheap to start again if you have a good Asian supermarket source. So, don't feel guilty if you lose it.
LINKS OF INTEREST:
http://en.wikipedia.org/wiki/Persicaria_odorata
http://davesgarden.com/guides/pf/go/310/
http://www.richters.com/Web_store/web_store.cgi?product=X1891&show=&prodclass=Herb_and_Vegetable_Plants&cart_id=5506611.16265
http://www.uni-graz.at/~katzer/engl/Poly_odo.html
http://www.soupsong.com/rlaksa.html
