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Charles Leach

 Though not native to Ohio, this attractive plant is a
better choice than its cousins.

Nymphoides cordata

Alternatives to invasive plants
Second in the series

Nymphoides cordata
(Water Snowflake)

by Charles Leach, Ohio USA
Click images to enlarge

For starters let’s get the disclaimer out of the way. The following is based on my personal experience with Nymphoides cordata, obtained from Ponds of Reflection in Florida, at our location in southern Ohio USA (zone 6). I cannot guarantee that the same species obtained from another source or growing in a different environment will perform in the same way.

According to the GRIN Database there are 38 species of Nymphoides recognized worldwide and, doing a little research, I found that there is a lot of variation within a given species and much confusion as to which species is which. During my search for examples of N. cordata, several potential sources that claimed that they had it had Nymphoides cristata instead. A couple went so far as to inform me that there was no "white snowflake" that would be hardy in zone 6.

Two years ago we bought two cordatas in the spring, potted them in 6" x 6" (15 cm x 15 cm ) containers and placed them in a 30" (76 cm) diameter x 12" (30 cm) deep tub outside that got sun about half a day. Both flourished while not overgrowing the tub or producing floating mats of stunted leaves as has always been the case with other Nymphoides for us.

One notable exception was Nymphoides peltata (common name yellow floating heart) which also remained in check when potted and placed in a tub. It was only when we made the mistake of turning it loose in our earthen pond that it went wild and took over. So far, attempts to control it mechanically have failed because practically every leaf that breaks off forms a new plant. Attempts to control it chemically have failed because new leaves sprout within days looking healthier than ever. Last fall we introduced grass carp, hoping that they might keep peltata in check but have little faith that it will work.  

Solid mat of Nymphoides peltata

Back to the saga of the cordatas. As winter approached year before last we removed the cordatas from the shallow outside tub. One was brought inside to winter under fluorescent lights in a heated tub and the other was sunk to the bottom of a 2' (60 cm) deep outside pool. The one inside died but the outside one came through winter just fine without dying back a bit.

Last summer the one remaining cordata was repotted and put back in the shallow outside tub where it again flourished but, with two exceptions, attempts to propagate it by planting viviparous sprouts failed so I gave up.

In October, as I removed the plant and its two rather tiny offspring from the shallow tub in order to move them to winter quarters in a deeper pool, I was surprised to find nearly a dozen viviparous starts with tubers nearly identical to those formed by the better known Nymphoides aquatica (common name banana plant) that is a popular aquarium plant.

After removing the baby plants from the leaves, I felt along the bottom of the tub and found over a dozen more. This was exciting but left me with a decision to make about how best to winter over the babies. Given the failure of wintering one of the originals inside in a heated tub, that wasn't an option for my newly discovered treasures, but I was not willing to place them at the bottom of an outside pool that would be iced over for much of the winter either. My solution was a sort of a compromise.  

After potting over two dozen baby plants in small drinking cup sized pots I placed them a little over 12" (30 cm) under the surface in a tub located in our attached but unheated greenhouse where water temperature has remained above freezing on the coldest days and approached 70°F (21°C) on sunny days. So far all seem to be surviving (as evidenced by the one in illustration #2 of a plant dug up and washed off to have its picture taken for this article) and a few have put up surface leaves.

If you are looking for a beautiful waterlily-like plant that is relatively trouble free, fairly shade tolerant, winter hardy and evidently not invasive, Nymphoides cordata might be the plant for you, but my usual warnings apply: 

1. If at all possible go with plants native to your region rather than bringing in an alien species that might become invasive.

2. Native or not, keep any plant you bring in contained and never make the mistake of turning it loose in a natural pond, lake or stream.

3. If a plant not native to your area reproduces by seed, dead-head it to prevent seed formation or contain and collect all seeds to be planted in containers.

Distribution of N. cordata
Map courtesy od Plants Database

So where is Nymphoides cordata native? According to the USDA Plants Database, it is native to eastern North America from Florida to Newfoundland, except for Virginia and Washington DC. I have no idea why it doesn't grow in that one area.

For information on other, better known, Nymphoides species check out David Curtright's Nymphoides and Villarsia article here

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