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Dave Brigante

Hardy Ferns for Ponds

by Dave Brigante, Oregon USA
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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 conditions.

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 other half.  

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 the spring.

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 didn’t 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 didn’t 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 ^

Sensitive 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 sun’s 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.   

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