Saturday, February 2, 2008

Hardy Ferns for Rock Gardens

From John Gilrein, Plant of the Month Coordinator:

Reference: Ferns for American Gardens, John T. Mickel, 2003, Timber Press

Almost everyone admires ferns for their grace and quiet beauty. In this article I will discuss ferns for 3 of rock gardeners’ favorite habitats, limiting the ferns discussed for woodland sites to some of the smaller ferns and ferns that grow naturally in rocky areas.

Ferns for Sunny sites

One does not normally associate ferns with sunny sites and well drained soils, but there are a few ferns that thrive in full sun conditions and very well drained soil.

1. Pellaea atropurpurea, purple cliff brake is an attractive fern that likes limey soil and sun. The fronds are from 8 to 20 inches long and evergreen. The leafstalks (stipes) are purple and the pinnae (leaflets) are silvery green. This fern is found over much over North America and Mexico and is hardy to zone 4.

2. Cheilanthes lanosa, hairy lip fern is more of a traditional looking fern than Pellaea with finely divided fronds. This fern occurs throughout much of the Eastern half of the US on rocky slopes, both calcareous (lime - rich) and non-calcareous and is hardy to zone 5.

3. Cheilanthes argentea, Asian lip fern has fronds that are deep green above and white underneath on reddish black stems. Forest Farm’s catalog reports that this fern grows in sun in soil of medium moisture conditions (moisture retentive soil with good drainage) and hardiness to zone 5.

My reference doesn’t include much detail on soil preferences for the ferns #1 and 2 above. I suspect these two ferns would prefer very well drained soil to rock garden conditions. P. atropurpurea has done well in my sunny rock garden for 2 growing seasons.

Ferns for Woodland sites

Most ferns are associated with woodland sites either with good drainage or wet soil conditions.

4. Asplenium platyneuron, ebony spleenwort, is small fern with narrow fronds (about 1 inch wide) 8 to 18 inches long with dark stems. It occurs in eastern North America in dryish soils and on rocks. This is reportedly easy. I have ebony spleenwort growing well (so far after 1 season) in a trough in part shade. It doesn’t need rocky soil, just good drainage and is evergreen and hardy to zone 4.

5. Asplenium trichomanes, maidenhair spleenwort, is a very small, delicate fern with narrow fronds 4 to 7 inches along with dark stems. It occurs across the northern hemisphere and grows in rock crevices and rocky slopes. This is an excellent fern for a trough. I haven’t grown it, but I would suggest gritty conditions with humus. It is evergreen and hardy to zone 2.

6. Asplenium (Phyllitis) scolopendrium, hart’s tongue fern is a rare fern reportedly found in only 2 of New York’s counties. It is also found in a few other states, Ontario, Canada, and Europe. This fern has evergreen, undivided strap like leaves, 8 to 16 inches long. Locally it inhabits north facing limestone talus slopes. The growing conditions provide a cool exposure, shade, and rich alkaline soil with good drainage. It is hardy to zone 5 and it more adaptable under cultivation. It needs a shady side with good drainage. There are hundreds of cultivars of this ferns with fronds that are wavy, crested, or divided, but not many of the cultivars may be available locally.

7. Adiantum pedatum, Northern maidenhair fern is a common fern that is found in most of Eastern North America. It grows up to about 2 feet high in rich, well drained soil in shade. The stems are purple or black, which creates a nice contrast with the green fronds. The maidenhair’s rhizome is a short creeping type which branches and can divided into separate plants. Northern maidenhair is hardy to zone 2.

8. Polistichum acrostichoides, Christmas fern, is an evergreen fern common in woods in our area and found throughout Eastern North America. The fronds are lustrous, dark green, and 1 to 2 feet long. This fern prefers moist woodland conditions with some lime, but will also do well on dryish soil in shade and is tolerant of acid soil. The crown of a mature Christmas fern is actually severally crowns crowded together on a short rhizome. The crowns can be cut apart to multiply the plant. It is hardy to zone 3.

Ferns for Water Gardens

The following ferns really are not ferns for rock gardens, but rock garden enthusiasts seem to appreciate ponds and bog gardens and these are great ferns. All three ferns below will be quite happy with saturated soil conditions.

9. Osmunda regalis, royal fern is beautiful fern that is worthy of its name. It is found in swamps and wet sites in North America, Europe, and curiously enough, tropical America as well. It grows in clumps from 2 to 6 feet tall. Royal fern will grow in shallow standing water or in normal garden conditions; it should grow tallest when grown in wet conditions. The more moisture it has, the more sun it can take. This fern can take neutral soil, but I suspect it prefers acid soils. It is hardy to zone 2.

10. Osmunda cinnamomea, cinnamon fern is named for the erect cinnamon colored fertile fronds (spore bearing fronds) in the center of the plant. Cinnamon fern is also found in swamps and wet places. It grows from 2 to 4 feet tall and needs acid soil. Similar to royal fern, this fern will grow in shallow water, and the more moisture it has, the more sun it can take. It will grow well in a shady site with good soil of the proper pH. If you don’t have acidic soil, it would probably grow well in a plastic pot sunk into the ground filled with rich, acidified soil. It is hardy to zone 2.

11. Matteucia struthiopteris, ostrich fern is tolerant of a wide variety of conditions. Its ideal habitat is rich, alkaline muck in a bright location, or humusy woodland soil with partial shade. It will grow well in decent soil with partial shade, and also well in full sun with wet soil. Ostrich fern’s feathery fronds grow 2 to 6 feet tall. It is a bit of a thug, spreading vigorously by underground runners, but is not difficult to control, so it is best planted where it has room to run. Since the fiddleheads of this fern are edible (and taste good), having a lot of it provides enough plants for a good harvest of an early spring vegetable. Ostrich fern creates a beautiful background in a wooded area, but the fronds tend to get brown and tattered by the end of summer unless they receive adequate water. It is found across the Northern hemisphere and is hardy to zone 2.

Sources for Fern Plants

(Numbers following nursery names designate which ferns above they carry.)

Eastern Plant Specialties - #4, 7, 8, 9, 10, 11

P O 385

Rahway, NJ 07065

Arrowhead Alpines - #4, 5, 6, 8, 9, 10, 11

P O Box 857

Fowlerville, MI 48836

Munchkin Nursery & Gardens – #5, 8, 9, 10,

323 Woodside Drive NW

Depauw, IN 47115-9039

Siskiyou Rare Plant Nursery - #1, 2, 4, 6, 7

2115 Talent Avenue

Talent, OR 97540

Forest Farm - #3, 6, 9, 10, 11

990 Tethrow Road

Williams, OR 97544-9599


Carol_E said...

I thought I'd paste Bill Plummer's comments here, as well as the space where he placed it (which felt a little buried in relation to this article). I remember some years ago our Chapter offered ferns for sale. I grew a couple very nice little ones - no recollection now what they were - in a woodland trough, until after several years they croaked. Here's Bill (who certainly has experience growing woodland plants in his garden) :

Just reread "Hardy Ferns for Rock Gardens". Missing are two Maidenhair ferns: Adiantum venustus, the Himalayan Maidenhair, and A. edatum subpumilum. Also missing is the Rockcap fern, Polypodium virginianum.

Bill Plummer

Carol_E said...

The latest issue of Trillium, newsletter of the Piedmont Chapter, NARGS out of North Carolina, has a very thorough article on rock garden ferns written by Tom Stuart. Tom hails from our neck-of-the-woods so to speak (Croton, NY) and will be presenting a program for them. Hmmmm . . . someone we might think about bringing to speak to us! You can access the Piedmont newsletter here although at this writing, this issue was so hot-off-the-press, it wasn't yet posted.