JARS v44n1 - Ferns For The Rhododendron Garden

Ferns For The Rhododendron Garden
Sue Olsen
Bellevue, Washington

I am a self confessed "propagation junkie" and, in fact, got my start with the serious stuff growing rhododendrons from seed. This procedure, as all propagators well know, requires carrying the progeny through several winters and blooming seasons to properly assess their value. As we live on a 1⅓ acre lot some of which is, by necessity, occupied by a house, I soon ran out of space. So it was that I turned to propagating ferns from spore - companions for my beloved rhododendrons, or so I thought. I soon became so fascinated with ferns' variety in form, texture and habit that they became my prime focus. I now consider rhododendrons as companion plants for my ferns! The wonderful result is that we can have it all, as rhododendrons and ferns are naturally compatible enjoying the same shade, soil and moisture requirements. And, as with a rhododendron planting, the fern choice is limited only by taste and climate. So pop a little good compost in your soil and let's take a look.

Worldwide there are some 10,000 plus fern species not to mention varieties, cultivars and yes, even hybrids. My discussion here of rhododendron companions is limited to a few of the many ferns that merit attention and has been drastically pruned to include those with maximum adaptability, cold tolerance and availability in the trade. Regarding the latter, I must add that I strongly oppose buying from nurseries that collect their plants in the wild. While they may appear to be wonderful bargains, the long term destruction of natural habitats is no bargain. In fact I think it should be illegal.

Just as one picks a rhododendron for a specific site and purpose - height, foliage, temperature tolerance and so on, the selection of the companion fern(s) deserves similar care with one major exception - blossom color. The flowerless ferns will not disrupt a progression of color or surprise you with an unexpected purple in the red bed. Rather, their green carpet gives unity to the blossoming landscape, simplifying design decisions for the collector who delights in having one each of a great variety of plants.

Ferns and rhododendrons in the landscape.
Ferns and rhododendrons in the landscape.
Photo by Sue Olsen

While ferns will never approach rhododendrons in height, there are some strong and stately tall species. The osmundas, although deciduous, are robust specimens usually around three feet tall. They are very useful in large scale design especially with the taller more open growing rhododendrons such as the Loderi aggregate. Their outline ranges from the Interrupted Fern, Osmunda claytoniana , with foliage at the frond's top and bottom and spore in between, to the Royal Fern, Osmunda regalis , with foliage suggestive of locust leaves. Two Japanese species, Osmunda japonica and O. lancea are similar in design, but lower growing (not to be confused with small.) Our native Onoclea sensibilis , the Sensitive Fern, can be planted under the osmundas where it will romp about and thrive especially in moist soil. Basically deciduous the spore bearing beadlike fertile fronds persist all winter and are joined in the spring with colorful new sterile fronds.

There are some tall polystichums that are widely used as companion plants. We in the west are most familiar with the Sword Fern, Polystichum munitum , a ubiquitous native that is extremely adaptable and were it rare would no doubt earn the respect it deserves. Like all the polystichums, it is evergreen. The sword shaped (naturally) fronds are usually about 2½ feet tall, but given a rain forest type environment can grow to five feet or more. Two other lesser known west coast relatives are also noteworthy for their strength and ease of cultivation. They are Polystichum andersonii and Polystichum braunii - Anderson's Fern and Braun's Fern respectively. Also tall, they are particularly attractive in new growth with their unfurling fronds cloaked in silvery scales.

The east coast commoner, Polystichum acrostichoides , the Christmas Fern, is somewhat lower growing, but popular and reliable in areas with severe winters. Their fronds are widely used as Christmas greens. There is no need to be seasonal however, as polystichum fronds can be picked for flower arranging from late spring onward. By initially placing the plucked frond(s) in hot water, they will last up to two weeks - frequently longer than the flowers they accompany.

Some of our best polystichums are imports. The British have very few polystichum species, but one, Polystichum setiferum the Soft Shield Fern, was at the Victorian zenith of ferny chic known to have 365 varieties. While two World Wars took their toll, a number of these Soft Shield Fern varieties are currently available on the American market. Polystichum setiferum var. divisilobum , incongruously called the Alaska Fern, has very finely divided fronds giving it a feathery appearance. With light green foliage and a relaxed habit, it is an excellent choice for areas of deep shade, as is its cousin Polystichum setiferum var. plumosodivisilobum .

Polystichum setiferum var.
Polystichum setiferum var.
R. yakushimanum
Photo by Sue Olsen

Polystichum polyblepharum , P. makinoi , P. neolobatum and P. rigens are a bristly and hardy lot from Japan. Admired for their shiny leafage, these medium sized plants may be used independently or grouped together to offer relief in somber sections of the woodland garden. They may, in fact, become the focal point!

The American wild lands are overrun with wood ferns (dryopteris), who furthermore are a promiscuous crowd so that sorting the hybrids has been the making of more than one doctoral thesis. While many of these are very attractive, for dryopteris with distinction, I prefer the Asiatic species. Dryopteris erythrosora , the Autumn Fern, so named for its spring color, and its var. prolifica both produce their new fronds in rosy red hues. They are wonderfully complementary with those of the rhododendrons that have red new growth, especially the lepidotes. One of my favorite plantings combines R. lutescens with an understory grouping of Dryopteris erythrosora and the yellow flowered, red leafed Epimedium sulfureum . Dryopfens bissetiana and D. purpurella , newcomers to the trade, are equally showy with their vernal foliage and have proven to be remarkably hardy. (Our 8 degree Fahrenheit 1989 winter, an experience I would not repeat by choice, did have its educational value.)

Several of the European dyropteris such as D. affinis and D. dilitata lepidota cristata (a botanical mouthful if ever there was one), have a heavy shag of brown scales on their emerging croziers. I like to use these as well as polystichums together with the beautiful assortment of rhododendrons that have tomentose foliage. For ferns with even darker scales, the Asian Dryopteris wallichiana , D. cycadina , and D. crassirhizoma are all top class evergreens.

New growth, Dryopteris erythrosora
New growth, Dryopteris erythrosora .
Photo by Sue Olsen

The cyrtomiums, holly ferns, are visually unfern-like. With large, frequently sickle shaped pinnae, they are very bold in design and should be placed accordingly, contrasting nicely with azaleas and small leafed rhododendrons. As many cyrtomiums have a matte patina and tend to be on the yellow side of green they also are a natural choice as companions for yellow flowered shrubbery.

Athyrium filixfemina is the Lady Fern. Anyone familiar with this species knows that she ain't no lady. She reproduces with abandon, often in the midst of a prized planting, and in no time at all that cute little sporeling has become a three foot tall eyesore. There are a number of filixfemina varieties with varying degrees of cresting, twisting and forking that are popular with those so inclined. These tend to be attention seekers, however, and should be planted as specimens rather than as background material. Not all athyriums are bad. The Japanese Painted Fern, Athyrium niponicum var. pictum is, as its name would suggest, one of the world's most colorful ferns blending shades of gray, blue, burgundy and green in varying intensity on its fronds. Here is a deciduous wonder to interplant with rhododendrons that are blue in leaf. Athyrium otophorum , while not as vivid in color, has a perpetually fresh appearance with its lime and wine colored fronds. It is an easier species to blend into the landscape design. Both are about 18" at maturity and extremely cold hardy.

If I could have only one fern in my garden, it would have to be the American Maidenhair, Adiantum pedatum . This graceful plant has tall brittle blackish stems topped with a flush of delicate outwardly spreading pinnae. Many of us know it as the five fingered fern. Deciduous, I think it looks best planted at stream's edge.

The evergreen Adiantum venustum from the Himalayas is a top candidate for lightening up any heavy planting and is one of my favorites for use with rhododendrons. The foot tall species spreads slowly via underground runners to eventually form a colony of delicate light green tracery.

Adianthum venustum with 'Noyo Chief'
Adianthum venustum with 'Noyo Chief'.
Photo by Sue Olsen

Another superb choice as a spritely ground cover is the Oak Fern, Gymnocarpium dryopteris . It will form a carpet in any friable soil and given moisture will send up fresh fronds throughout the summer. Although deciduous, it can be planted with Cyclamen hederifolium to provide a succession of greenery.

For a truly unusual fern, we have several that are vines. The Hartford Fern, Lygodium palmatum , has for decades resisted domestication and should be left undisturbed in its few remaining natural habitats. The Japanese Climbing Fern, Lygodium japonicum , is just the opposite and will willingly climb whatever is handy, be it your lace curtains indoors or your rhododendrons outdoors. It clings by twining rather than tendrils and must be cut to the ground annually to prevent an unsightly snarl of new and old fronds.

Some ferns, like some rhododendrons, are at home in a sunny or partly sunny location. Amongst the most striking are the cheilanthes which are sun screened with silvery and rusty scales and hairs - a kind of botanical weatherproofing. As beautiful as they are, their exacting requirements make them best reserved for the truly dedicated pteridomaniac. An easier option is the Rustyback Fern, Ceterach officinarum aka Asplenium ceterach by Anglophiles. It can be cultivated in full sun and is especially attractive planted in a lime supplemented (eggshells or chunks of broken concrete will do) rocky niche. The chubby little 4-6" fronds are scalloped along the edges and decorated on the underside with russet hairs, hence the common name. If allowed to dry out, it will feign death and curl up in a tight little bun. A good drink will give it new life assuming the neglect has not been too prolonged.

Another species for the sunny border is Blechnum pennamarina . This low creeper is not fussy about soil or site. The sun reduces its size and intensifies the frond's natural russet color thus enhancing its value as a compact ground cover.

The dwarf maidenhair, Adiantum pedalum var. subpumilum tolerates more sun than most ferns and will indeed become more diminutive and imbricate as exposure is increased. (Please not to excess!) A miniature version of the type it is much in demand and especially valued for its refined silhouette. This is the dignitary of the foreground planting.

Adianthum pedatum var. subpumilum with
R. nakaharae
Adianthum pedatum var. subpumilum with R. nakaharae
Photo by Sue Olsen

The little aspleniums particularly Asplenium trichomanes and its varieties with their black stipes (stems) and rounded beadlike pinnae are excellent evergreen alternatives. They adapt to a full range of exposure from deep shade to partial sun though they must be spared intense midday sun. There are many other aspleniums, all small, evergreen and individually charming, that given a rocky habitat can be successfully added to a fern collection.

This is but a sampling of the many ferns available to compliment your rhododendron planting. Who knows, as you take a closer look, you too may be on the path to a new addiction!

Sue Olsen is the owner of Foliage Gardens a specialty fern nursery in Bellevue, Washington. She grows fern from spore collected throughout the world.