Hardy Ferns for Ponds
by Dave Brigante, Oregon USA
Click images to enlarge
In recent years I have contemplated running some informal
experiments on an assortment of hardy ferns that may have potential
for surviving in a pond setting. I researched which ferns already
enjoyed living in very moist soil environments and decided to
procure enough to do some of testing and also have enough to
sell through both our retail store and our wholesale division.
After consulting with a reputable fern nursery in Texas USA,
I ordered six flats of ferns, three in 40-cell trays and three
in 72-cell trays. The plants arrived in early November of 2007,
not the best time to start my experiment, but if I really wanted
to test over an extended period, anytime was a good time for
me to start.
The first thing I did after releasing the plants from their travel
boxes was to plant one of each variety into pea gravel in 3.5"
(9 cm) pots. I placed them directly into water at a level that
covered the tops of the pots but only came up to the bottoms
of the plants crowns. By using only pea gravel I could
see if the ferns could survive inundated in water as very young
plants without my needing to worry about any soil fouling. This
could affect the young plants overall vigor. These plants
were left in a greenhouse where the minimum cool season temperatures
would not fall below 50 F (10 C) and were kept in somewhat shady
The smaller 72-cell-sized ferns were put into 3.5" (9
cm) pots using a general potting mix. The goal was to grow them
to a size that would be appropriate for transplanting into 1
gallon (4.4 liter) nursery pots the following spring, The rest
of the 40-cell ferns were put directly into 1 gallon (4.4 liter)
nursery pots using purely aquatic soil for half and a mix of
50% general potting soil and 50% aquatic soil was used for the
Those specimens were put in a greenhouse held at about 40 F (4.4
C) through the winter. I used half strength liquid fertilizer
applied as needed. Because the sunlight here in Oregon USA is
so diffuse through the winter no special care was required to
shade the plants.
Young ferns under a greenhouse bench
To further test these ferns in a water-laden environment, I put
five of each variety planted in the aquatic soil into water filled
no-hole trays. Five of each of those in the 50-50 mix were also
put into water filled trays. All were kept fairly cool until
As the temperatures began to pick up, the ferns all started to
come back to life. Some had gone totally dormant, losing all
of their top growth, while others stayed visibly green but needed
some general grooming. To my pleasure all of the plants that
had been left in the water trays came back after their four month
dormancy. I continued to give them the liquid fertilizer and
increased the rate to get them to green up a bit. At this point
it didnt seem to matter which type of soil they had been
growing in, as they all looked about the same.
The initial test lot that I had kept small and in the pea gravel
also came back quite well, but when I examined them out of the
water, it became apparent that there had been little or no rooting
to anchor themselves into the pots. I gathered from this that
they either need finer soil than just pea gravel or that, if
they are grown in water, they may grow more as surface rooters.
The gallon pots that had been sitting in the shallow water trays
throughout the winter did have roots heading downwards in their
pots but not to the bottom where the soil was super saturated.
At this point placing the 1 gallon (4.4 liter) plants directly
into deeper water didnt seem like an option until more
rooting had taken place, so we waited.
This is a good time to talk about the varieties that were
chosen for this informal experiment. Some have been kicking around
in the water plant industry for a number of years and a few not
so much. The one that I have seen being sold the most of my group
is one called simply marsh fern (Thelypteris palustris).
It grows as a mass that stays about 18-30" (46-76 cm) tall
and is well known as a premier bog fern. The next one is called
sensitive fern (Onoclea sensibilis). The 12-36"
(31-91 cm) pale green fronds can tolerate sun or shade if kept
well moistened, and is considered to be an aggressive grower.
There are two royal ferns that are a part of this
clan as well. The first is the American royal fern (Osmunda
regalis var. spectabilis) that, once established and
being an evergreen, will show off its almost 3' (91 cm) tall
foliage well into winter. Its cousin, the purple stem fern
(Osmunda regalis purpurascens), is also a robust grower
topping out at 4' (122 cm) after a few years, all the while producing
unique purple newer growth that can create an alluring focal
point in any garden.
A third Osmunda fern, also known as cinnamon fern
(Osmunda cinnamomea) is an eye catching specimen in its
own right, creating cinnamon-colored fronds that become spirelike
sentinels. Reaching 5' (152 cm) tall at maturity, you have to
see it to believe it. The last fern is the Virginia chain
fern (Woodwardia virginica) which tends to migrate
slowly through boggy settings. The fronds have very black stems
that contrast extremely well with the olive green new growth.
Very tough fern.
American royal fern
< Marsh fern | Purple stem fern ^
After waiting out the full spring growth of the ferns, I moved
twelve 1 gallon (4.4 liter) plants of each soil style into a
water depth that once again only came up to the plants
lower crown areas. I used two of each variety and put pondtabbs
into six of each of the two groups of twelve. As you might imagine
the plants that received the fertilizer stayed much greener than
the unfertilized plants.
The move out of the greenhouses and into the outdoor trough happened
in July, well after the rooting process had been completed. I
set up a miniature shade cloth enclosure, pictured at right,
to protect these shade lovers from the suns harsh rays
until our fall rain began and clouds once again became a part
of our ever evolving skyscapes.
The ferns in general did quite well, but I think I should
have been a little more consistent with the pondtabbs to keep
them looking greener, I only gave them the tabs a couple of times
and I would certainly recommend starting that process much sooner,
say in April or May after the new growth has kicked in.
In the 2009 season I have been giving all of the plants a
single pondtabb each month and all are showing vigorous new growth
except for the cinnamon ferns, which are alive but are coming
on much more slowly than the others. It appears more and more
that this variety is not a good candidate for use as a pond plant.
Hardy ferns in a bog garden
As far as plant hardiness is concerned, this past winter could
not have been a better situation for testing these plants in
USDA Zone 8, as we had a record snowfall of over two feet (61
cm) that stayed on the ground for more than three weeks. At one
point the temperatures at the nursery dipped down to 12 F (-11
C). Now with summer in full swing I feel very confident in these
plants abilities to live in a pond setting, after being
in the same watery environment for what has now exceeded one
full year. The jury is still out on the cinnamon fern.
Soil-less root system
of a royal fern
The smallest plants, those in the pea gravel, are also coming
back but are mostly living as floating ferns. This may suggest
that they would be excellent floating island selections as long
as some shade is provided. Based on this trial I conclude that
these ferns will in fact live in water as potted plants, as long
as an ample root system has been previously developed. In the
coming months I plan to place a few of the ferns that have been
treated as terrestrial plants directly into water up to the crown
level to see how they react.
Hardy ferns in a moist soil garden
Whether they are grown as pond marginals with little anchor roots
or as potted submerged pond plants, using ferns tucked into the
small shady alcoves of our ponds or as accents in water bowls
on our decks or patios (preferably with only morning sun) are
realistic possibilities to consider.