As improbable as it seems, Boulder County is home to many ferns, some of which could grow in your garden.
By Panayoti Kelaidis
It would be entirely possible for someone to grow up in Colorado and never notice a wild fern growing anywhere in the state. Unlike maritime climates, where whole hillsides and woodlands are carpeted with ferns, Colorado’s 70 or more ferns and fern allies are introverted to the extreme.
Many of our wild ferns are small, tucked tactfully among giant boulders. The larger ferns are often scarce and modest, only found in a few spots where not many hikers wander. And quite a few might not even be recognizable as ferns—the “hot-rock” or desert ferns, which it’s true are fernlike in shape, but covered in silvery or gray hairs, or have an almost aluminum-like feel and texture. These ferns are not by any means common, although a few canyons exist in southeastern Colorado where four or five kinds mingle.
When you do find a ferny spot in our state, it can be very special. The lower reaches of the western side of Rabbit Ears Pass, for instance, have aspen forests filled with masses of bracken fern that are quite visible from the car, even if you are speeding by. A rancher in southeastern Colorado once invited me to visit a wet cliff near her home that was festooned with enormous and delicate swaths of Venus-hair fern that were easily 50 feet across and tall (a spectacle I will not soon forget).
But perhaps because these ferny moments are so rare, and our encounters so brief and special, ferns resonate here, more than they would where ferns are commonplace and taken for granted.
Boulder County is home to some very special fern haunts. A half-dozen species of hot-rock ferns readily grow here and there on Flagstaff Mountain (one of them, Pellaea wrightiana, is not found elsewhere in the state until you practically reach Oklahoma). Ebony spleenwort (Asplenium adiantum-nigrum) fills a seam between the White Rocks on Boulder Creek, and otherwise only grows in North America in one Arizona canyon and a mountain in Chihuahua, Mexico (although it is abundant in Eurasia and Africa). A short way above tree line on Pawnee Pass, observant hikers will notice a dozen or so huge clumps of alpine lady fern (Athyrium distentifolium var. americanum) growing right next to the trail. This beautiful and rather rare fern always grows at altitude.
The state’s most dramatic—and garden-worthy—fern is the stately male fern (Dryopteris filix-mas). It grows abundantly in a few shady spots in Boulder Open Space and Mountain Parks. This fern is likewise a common fern in Eurasia, but in North America it is quite rare and sparsely distributed outside the Boulder area.
It could be said, then, that Boulder County is the state’s fern capital. So shouldn’t we consider planting some of these impressive plants in our gardens?
Fortunately, almost every local independent garden center has a “fern corner” where you’ll find a half-dozen or so fern species.
Planting and growing ferns is not rocket science. Although you often find ferns thriving in some pretty rough spots, they do best in a soil amended with a lot of compost and humus, and they benefit from an annual mulching with a layer of leaves an inch or so deep.
Although a few ferns tolerate quite a bit of sun, I’d pick a shady, sheltered spot if you want to be sure to succeed. The north side of a house is ideal, or plant ferns underneath redbuds, locusts or perhaps fruit trees, which tend to have deeper roots and don’t cast too dense shade. Clip leaves at their base when they start looking weathered.
Be sure to keep ferns moist the first year you plant them, but once established, most ferns don’t usually need much more water than most garden perennials. In fact, they are carefree and quite long-lived. Some can even spread enough at the root to become a minor pest if you put them in the wrong spot. But not a problem! Your friends will be happy to relieve you of some of your excess ostrich fern (Matteuccia struthiopteris).
I’ve grown more than 100 ferns at any given time in my rather ferny lifetime in the state. But there are a few ferns I would never want to be without, and if you grow them I think you’ll become equally smitten. Here are my favorite to-die-for ferns:
Maidenhair Fern (Adiantum pedatum)
This gorgeous fern grows in one small canyon south of Ouray (and none other, thus far), but it’s abundant in the Pacific Northwest and quite common in much of the eastern United States as well. The plant’s graceful, arching sprays of delicate Irish-green foliage shiver in the breeze and provide a focal point that can transform any shady corner of your yard.
Although maidenhair fern occasionally appears in local nurseries, it’s most often sold through mail-order nurseries that specialize in wildflowers (luckily, there are many of these). Last fall I was astonished to see a large bench at a local big-box store full of Himalayan maidenhair fern (Adiantum venustum), which is much less frequently sold at nurseries but has proven to be even tougher in my experience than its American cousin. This ground–covering fern grows to a height of only 7 to 8 inches and its foliage is quite evergreen—it’s a plant worth seeking out.
Male Fern (Dryopteris filix-mas)
Our trusty Boulder County specialty is occasionally sold by retail garden centers, and if you find one, snatch it up! This is one of the most aristocratic garden plants, with semievergreen foliage that starts out light green in spring and darkens to a rich emerald in summer. I have grown clumps of this fern that have lasted many decades without showing any sign of senescence. I would plant almost any type of shield fern (Dryopteris)—all are elegant and most are similarly accommodating.
Lady Fern (Athyrium filix-femina)
I recall hiking along the Middle Saint Vrain River in western Boulder County many years ago and seeing dozens of enormous clumps (some nearly 4 feet tall) of the delicate lady fern along the streamside. It grows at higher elevations than the male fern, and usually closer to water. The commonly sold forms belong to a different eastern subspecies that usually grows only 2 feet or so tall. But it is long-lived and carefree in the garden.
Sword Fern (Polystichum sp.)
You cannot make me pick from the many kinds of sword ferns, because they are all too wonderful for words. Unfortunately, our only native species (Polystichum lonchitis) requires very cool conditions at higher altitudes to thrive. I have only seen this once or twice on cliffy sites in subalpine forests in Boulder County. But its closely related cousins adapt wonderfully to local gardens.
Christmas fern (Polystichum acrostichoides), with its long, strappy, evergreen leaves, is easy to find at nurseries. But my two favorites are the numerous selections of hard shield fern (P. aculeatum) and soft shield fern (P. setiferum). These two common European sword ferns were bred into innumerable selections during the mad “fern craze” of the Victorian era, when enthusiasts grew thousands of kinds of ferns in outdoor gardens and “ferneries”—greenhouses designed to grow ferns.
Even if you’re not ready to erect a Victorian fernery in which to serve tea to your guests, I encourage you to grow a small fern patch with a few shade-loving bulbs and wildflowers to refresh both your garden and spirit during the long, hot summer months.