Building a Fern Bed to Reduce Erosion

Our new garden space held after thunderstorms and heavy rain overnight.

Rainy weather and frequent storms over the past few years have presented a particular challenge.  We are situated on a sloping bit of land on the side of a ravine.  A creek runs through the ravine below us and empties into a small lake.

Working with the continual erosion has remained a constant theme of our gardening here.  Our challenge is to slow the flow of water to increase opportunities for rain to soak into the soil for later use, while reducing the amount of flowing water that erodes the soil and runs off into the ravine.

We minimize digging holes for new plantings, preferring instead to plant in raised beds and to plant small plants with small roots, allowing them to grow into the banks to hold them, over time.  We’ve added large amounts of topsoil, compost and gravel over the years to fill holes and anchor new planting beds.

All of this takes time and investment.  We work on it a little more each season.  This spring we chose an area where the erosion has been particularly worrisome over the past few years.  Our smaller efforts to control the flow of water were insufficient, and so we planned a more comprehensive project to finally address the area and transform an eyesore into a beautiful extension of our fern garden.

The fern garden has grown each year over the past decade, as we introduce ferns to more and more shady areas where water flows downhill.  We like ferns.  We enjoy the variety of their forms and growth patterns.  And we have learned that their fibrous roots do an exceptionally good job of holding the soil while their fronds protect it from beating rain.  Ferns quickly absorb and process storm water run-off.

Two years ago, we installed concrete pavers at the top of this steep wash to slow the run-off and planted a few evergreen Autumn ‘Brilliance’ ferns in an area where water had cut deep ruts.  The ferns have prospered, but erosion continued in the areas around them.  We could see where storm run-off was washing around the blocks and running downhill during heavy rains.

This large area requires a large solution.  We ordered two sizes of landscaping blocks, paver base and topsoil to fill in eroded areas and establish raised planting beds between the rows of blocks. 

We set several lines of the larger blocks along the contours of the slope to gradually slow the flow of storm water and encourage it to soak into the ground.  I set another line of the smaller blocks to create a small planting area with amended soil for our new Asplenium ferns.

Concrete pavers, ceramic pots and natural stone not only interrupt or direct the flow of running water, but they also slow it enough to allow more to soak into the ground.  The ground beneath them remains cool and damp; an excellent place for roots to grow.  Planting right beside the pavers either uphill or downhill gives the plant a competitive advantage, and the plant’s roots and leaves further protect the soil and further slow the water’s flow.

I am using a combination of native and non-native ferns with various growth habits in this space.  Some are evergreen, and others deciduous.  I have also transplanted Helleborus seedlings along the bottom and side edges of the plantings.  These relatively large, spreading evergreen plants with large leaves protect and hold the soil.  They bloom from winter through late spring and protect the area from tunneling rodents. 

Hellebore seedlings anchor the area below the pavers, and Christmas Ferns grow in the space above. Autumn Fern ‘Brilliance’ anchors the tier above the Christmas Ferns.

Native Viola labradorica, the common violets that often crop up in the lawn, already volunteer in this area.  Left alone, they form dense mats and spread themselves around.  They bloom each spring even in shady areas.  I am careful to leave them, even as I pull out other natives, like wild strawberries.

We will encourage mosses and native Viola labradorica, with its heart shaped leaves, to fill in spaces between the ferns.

The very top area of the space, above the first row of blocks, is now covered with Ajuga divisions and anchored with two Heuchera.  These mat forming perennial ground covers bloom in late spring and early summer and will thrive in partial sun.  I’m confident they will help stop the flow of water across the top edge of this bank in all but the heaviest downpours.

Ajuga reptans ‘Black Scallop’ sends out runners in all directions. A new plant will root at the end of each runner, soon forming a dense mat of vegetation to protect the soil.

The goal, as always, is to establish a plant with the smallest root system practical and allow it to grow into the space.  Areas excavated for planting should be packed back firmly, protected from direct run-off, and mulched.  We have found a pea gravel mulch highly effective on slopes.

I began ordering bare-root ferns this year in February.  I ordered a few unusual ferns, and then added a ’10 fern grab bag’ to see what would come.  It was a very nice mix of varieties, with at least two plants of each of five different ferns.

Aspleniums grow best in limey, rocky soil. This small area, heavily amended with gravel, is planted with Ebony Spleenwort and Walking Ferns. Two more Asplenium species will be planted into the space below.

I knew that I wanted to establish a new fern bed this year but had not decided exactly where all of the new ferns on order would grow.  I followed up that February order with more ferns orders for several unusual ferns carried by Plant Delights Nursery, and other vendors. 

As I began clearing a much easier, more accessible site for a very conventional fern bed, I noticed this sloping, eroded bank that desperately needs attention.  The Redbud tree growing at the bottom of the slope fell over in a storm in 2019, and has survived, making the area even more challenging to tend. Building here required a bit more effort but will help heal a troubled area of the property while providing an excellent display area for these many new ferns.

With the first stage of planting completed, I’m still waiting for two fern orders to complete the project.  With heavy rain on the way through the weekend, I bought a few ferns already in leaf, locally, and planted them to help hold the area while waiting for the bare-root ferns to grow in and begin to spread.

One entire level of the new bed is devoted to Aspleniums.  I made a narrow planting area and used paver base below the topsoil to create a shallow, rocky, limey soil.  Aspleniums thrive where most other types of ferns would wither.  They like close quarters and often grow in masonry, on rubble, or over limestone rocks.  That area is planted with Walking Ferns, Asplenium rhizophyllum, and Ebony Spleenwort, Asplenium platyneuron.  Hybrid Asplenium x ebenoides, or the Dragon’s Tail Fern, and Asplenium scolopendrium, or Hart’s-tongue Fern, coming from Plant Delights, will join them later this month.

Athyrium niponicum ‘Godzilla’ grows in the pot and Athyrium otophoum, or Eared Lady Fern, grows beside it, anchoring this upper portion of the bed. Athyrium niponicum ‘Joy Ride’ will grow in the center of this section.

There will also be several varieties of Athyrium, the Lady Ferns.  Species of Athyrium can be found on several continents.  The Japanese Painted Fern, Athyrium niponicum, have been highly hybridized into endless varieties of color and elaborately crested forms.  I moved a potted Athyrium niponicum ‘Godzilla’ to this new space on one of the upper levels.  I may eventually plant it, but don’t want to dig a hole large enough for its roots until this area has knitted together and the erosion problem handled.  This vigorous fern can grow to 36” tall and spread to 6’ or more across.

Athyrium niponicum ‘Pictum’ grows nearby in the established section of the fern garden. It has reproduced, and I am finding babies that can be transplanted.

I have Athyrium niponicum ‘Joy Ride’ also coming from Plant Delights.  Heavily crested, this silvery beauty will grow to 20” tall and several feet wide.  But since it comes in a very small pot, I can plant it right away in a prominent spot.  This is a beautiful fern that I’ve never found locally but have wanted to add to our garden for quite a while.

We are also growing the beautiful Athyrium filix-femina ‘Lady in Red,’ and Athyrium otophoum, or Eared Lady Fern.  Both of these sport burgundy red stipes and lime-green foliage.  

There are also several species of Adiantum, or Maidenhead Ferns.  Of particular interest is the native A. pedatum, or Five -Finger Fern with its distinctively curling stipes.  There is an A. venustum, or Himalayan Maidenhair in a small pot, and I expect to add Southern Maidenhair in the next few weeks.

Himalayan Maidenhair fern grows in the small pot. It is marginally hardy here, but survived winter outside in another section of the fern garden. Autumn ‘Brilliance’ fern, a Dryopteris or wood fern, grows to the left.

I think it is interesting to grow several different species from the same genus side by side so you can get to know them by their similarities and differences.

Finally, in addition to the Dryopteris erythrosora ‘Brilliance’ planted some years ago in this space, there was also a Polystichum acrostichoides, or Christmas Fern, already growing here.  Christmas Fern has naturalized in our garden and pops up in unexpected places.  I have added three more Christmas Ferns in the bottom tier of the space.  Not only are they evergreen and tough, but they will grow quite large, and finish the job of stopping any run-off from leaving the bed.

Fiddleheads on an established Christmas fern grow surrounded by native Mayapples, Podophyllum peltatum.

Over the past few years of actively cultivating moss as a ground cover in shady areas of our garden, it has spread itself around and filled in more and more areas where grasses and wildflowers once grew.  Moss is an attractive, very low maintenance ground cover that doesn’t mind foot traffic.  I am transplanting clumps of moss into this new planting area around newly planted ferns with the expectation that within a year or two, it will naturalize between the ferns so this new garden space blends into the surrounding bank.

We are looking forward to watching these ferns grow over the next few months, and I will make this bed a regular stop as I wander the garden with camera in hand.  I plan to feature several of these beautiful ferns in future posts, and also show you a few more varieties, not mentioned here.

Ferns are some of our most useful plants for transforming problem areas of the garden into functional, beautiful spaces.  They are especially useful where running or standing water needs management, and in deep shade where little else might grow.  Combined with mosses and low ground cover, they grow into a restful, peaceful scene of rare beauty.

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