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Though not native to Ohio, this attractive plant
better choice than its cousins.
Alternatives to invasive plants
Second in the series
by Charles Leach, Ohio USA
Click images to enlarge
For starters lets 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
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