Hardy Ferns: Shady Characters of the Plant World

Moist, shady locations in the landscape often present a dilemma for gardeners in that the thought of a green plant thriving without much light is somewhat of a paradox. Hardy ferns represent an interesting, attractive solution for such problem areas and deserve to be more widely planted than is currently the case. Hardy ferns are simply ferns that can withstand the rigors of a typical Midwest winter. Many hardy ferns are equally tolerant of warm temperatures making them ideal choices for Missouri gardens.

Ferns belong to the plant phylum Pteridophyta and are considered to be lower, more primitive forms of life than plants most ornamental plants which are members of the Anthophyta or Coniferophyta phyla. The latter constitute the angiosperms and gymnosperms (respectively) which flower and bear seeds whereas ferns do not. Instead of seeds ferns bear reproductive bodies known as spores in structures called sori located most often on the underside (often around the margins) of their leaves which are called fronds. Ferns exhibit a basal form of growth with fronds arising directly from a crown which is at or near the surface of the soil. The main axis of the frond is known as the rachis which branches in certain ferns to form a structure not unlike a compound leaf in appearance. Individual segments on the rachis are known as pinnae which may or may not be divided further into pinnules. The latter give ferns their light, feathery appearance.

Most ferns are denizens of the forest floor where the soil is highly organic because of the breakdown of leaves over decades of time. Therefore an ideal soil for ferns is one rich in organic matter. In heavy soils, four to six inches of welldecomposed organic matter should be incorporated before planting to facilitate drainage. Haydite or crushed granite (poultry grit) also work well to facilitate drainage and can be used in addition to (not instead of ) organic matter. Sandy, light soils lack the ability to hold enough water to please most species of ferns and also should be amended with organic matter before planting. Ferns prefer soil a bit on the acidic side with a pH range of 4 - 7 considered acceptable.

Native to forest floors, most ferns do not need or like direct sun. Full shade to part-shade is an ideal exposure for most ferns although some species are more tolerant of sun than others. Adequate moisture along with high humidity also are required by ferns; fertilization should be done in the spring after new growth begins to emerge.

Ferns are “light-feeders” which are quite sensitive to excess fertilizer salt in their root area. Slow release fertilizers (e.g. Osmocote) or complete organic fertilizers work well for ferns since they tend to release their nutrients over time thus avoiding salt stress. Additionally, ferns benefit from the application of an organic mulch (e.g. leaf mold or pine straw) to aid in water retention and control weeds. The latter are not a great problem since most weeds need more light than ferns thrive under.

Ferns have few cultural problems if their environmental needs are properly met. Snails and slugs sometimes feed on ferns and can be controlled with poisonous baits or diatomaceous earth. Scale insects are know to infest ferns and can be controlled with appropriately labeled insecticides. Insecticidal soap or horticultural oil are two "low risk" pesticides that might be considered for scale and other insect control.

There are hundreds of species of ferns with ornamental merit ranging in height from several inches to over six feet. Many are native to North America. Below are eight of the more popular species which grow well in our area and should be readily available in commerce for those wanting to add some interesting foliage to a shady area.

Christmas fern (Polystichum acrostichoides). Upright, leathery, evergreen fronds 24 to 36 inches tall. Native to eastern North America. Prefers light shade to full shade and constant moisture; can withstand some drought. Useful border plant; fronds can be used in flower arrangements.

Cinnamon fern (Osmunda cinnamomea). Upright, deciduous fronds 24 to 36 inches tall. Native to North America. Very tolerant of exposure–sun to full shade. Can stand some drought when located in shade. Dimorphic: has both sterile and fertile fronds. Unique cinnamon-color because of “wooly-natured” fertile fronds.

Japanese Painted fern (Athyrium nipponicum ‘Pictum’). Dark wine-purple deciduous fronds 10 to 15 inches tall gradually change to silvery-green. Very colorful. Light shade to full shade preferred along with constant moisture. Can stand some drought in more shady exposure. Recent Perennial Plant Association “Plant of the Year”.

Lady fern (Athyrium filix-femina). Upright, vigorous, deciduous fronds 24 to 48 inches tall. Native to North America. Light shade to full shade preferred along with constant moisture. Slightly drought tolerant. Very lacy, delicate foliage.

Leatherwood fern (Dryopteris marginalis). Sometimes called Marginal Shield fern. Leathery, evergreen fronds 24 to 36 inches tall. Native to North America. Prefers light shade to full shade and constant moisture; can withstand some drought. Evergreen foliage provides year-around effect. Deep green frond color compliments wildflowers nicely.

Northern Maidenhair fern (Adiantum dedatum). Thin, wiry rachis forms fronds 12 to 20 inches in height that are somewhat the shade of a horseshoe. Deciduous. Native to North America. Light shade to full shade preferred along with constant moisture. Can withstand some drought. One of the more petite, fine-textured ferns for the garden.

Ostrich fern (Matteuccia pensylvanica). Vase-shaped, deciduous fronds 48 to 72 inches in height. Dimorphic. Native to North America. Name derived from outer (sterile) fronds which are very lacy in appearance. Prefers light shade to full shade along with constant moisture. Does not tolerate dry soil. Large and showy.

Royal fern (Osmunda regalis). Coarse-textured, deciduous fronds 48 to 72 inches in height. Fronds reddish in color when unfurling and later turn green. Shape of pinna cause fronds to resemble branches of black locust tree. Native to North America. Tolerates exposure from sun to full shade and prefers constant moisture. Large fern that can tolerate some sun.

David Trinklein
Associate Professor of Horticulture