Autumn Fern (Dryopteris erythrosora)

Autumn Fern, Japanese Shield Fern, Shaggy Shield Fern

Also known as Japanese shield fern or Japanese wood fern, autumn fern (Dryopteris erythrosora) is a hardy plant suitable for growing as far north as USDA hardiness zone 5. Autumn ferns in the garden offer beauty throughout the growing season, emerging coppery red in spring, eventually maturing to a bright, glossy, kelly green by summer. Read on to learn how to grow autumn ferns.

I. Appearance and Characteristics 

Dryopteris erythrosora, the autumn fern or Japanese shield fern, is a species of fern in the family Dryopteridaceae, native to east Asia from China and Japan south to the Philippines, growing in light woodland shade on low mountains or hills.

The specific epithet, erythrosora, is derived from two Ancient Greek words, ἐρυθρός (eruthrós) meaning red, and σωρός (sōrós) meaning heap. So erythrosora literally means red heap, referring to the red sori on the undersides of the pinnules. The specific epithet may really be a reference to the red indusia, which cover the sori.

It is semi-evergreen (in cooler climates), with bipinnate fronds 30–70 cm (12–28 in) tall by 15–35 cm (6–14 in) broad, with 8–20 pairs of pinnae. The fronds have a coppery tint when young, but mature to dark green. It has an upright to down-lying rhizome which is thick and branched, so that it forms several crowns.

The leaves are funnel-shaped with the top ones being leathery shiny, divided twice, triangular in shape and pointy. The individual leaflets are narrow lanceolate. Its edge is almost completely sown up.

The leaf stalks are about a third as long as the leaf, striated, yellow to red, with linear to lancet-shaped brown scales, containing two large and several small vascular bundles in a cross-sectional drawing.

When budding, the young fronds are coppery red and later green. There can also be several leaf outlets per year. The spores, which are kidney-shaped, become ripe between summer and autumn.

Dryopteris erythrosora can tolerate a drier soil than many ferns, but is most successful in moist, humus-rich soil, with a pH range of 6.1 to 7.5, with morning or late afternoon sunshine but not during the middle of the day. It is hardy zones 5 to 11. Propagation is by division in spring, separating the small crowns from the larger crowns, or by spores. It is raised as an ornamental plant in gardens because of its color change in the foliage, which change from dark red to dark green, but not very often.

D erythrosora and the cultivar D. erythrosora ‘Brilliance’ have gained the Royal Horticultural Society’s Award of Garden Merit.

II. How to Grow and Care

Sunlight

Autumn fern needs to be planted in a shady location. Too much light is detrimental to its health and can sunburn it to the point of killing it.

Temperature and Humidity

Autumn fern can grow in a fairly wide climate range; it tolerates both freezing winter weather and does well in moderately warm summer temperatures and high humidity. However, it does not do well in hot or dry weather, and it is especially vulnerable to drying winds that parch the soil.

In the lower range of its climate zone spectrum, in USDA zones 5 and 6, the foliage might die back during the winter but will bounce back in the spring.

Watering

Until it is established, during the first growing season, a newly planted autumn fern needs regular watering in the absence of rain. In climates with regular rainfall, watering is not necessary. In drier climates, or during dry spells or extended droughts, water the area around the plant slowly and deeply to keep the soil moist, ideally with a soaker hose.

Similar to all container plants, potted autumn ferns need frequent watering several times a week in hot weather to keep the soil moist at all times.

Soil

The soil should be similar to conditions in the fern’s native woodland habitat in eastern Asia: acidic with a pH below 6.0, containing a high amount of organic matter, consistently moist but with good drainage.

Fertilizing

Autumn fern that has been planted in soil high in organic matter only needs a springtime application of a complete all-purpose fertilizer.

Container plants need to be fertilized more often, about once a month during the growing season.

Pruning

Autumn fern does not require pruning, in fact, when the old fronds wither over the winter, it is important to leave them on the plant. When they die down in early spring to make room for the new fronds, you can remove them for a neater appearance but be careful not to damage any new growth at the crown.

Propagation

You can propagate autumn fern by division or by spores.  Division is the easiest and therefore recommended method. You’ll need a mature specimen, one that is showing a bare center which is a sign that the plant needs to be divided to rejuvenate it.

  • In the spring, when you see the first new fronds emerge, dig out the entire fern and all its roots (rhizomes) with a shovel.
  • Separate it into smaller segments using pruners. Make sure that each segment has at least one growing tip with sprouts on it from which the fronds will emerge.
  • Dig a hole slightly deeper than the root system. Add a few handfuls of organic matter and place the segment in the hole. Backfill with soil and gently press down on the soil. Water well and keep the new fern well-watered in the absence of rain until you see new growth and the plant is established. 
  • A more involved and lengthier method is propagation from spores that you have collected yourself. This process can take 6 to 12 weeks. 

Potting and Repotting 

You can also grow autumn fern in pots, as a houseplant or for a patio or balcony.

Select a pot, preferably clay or terracotta, with large drain holes. The pot needs to be tall and wide enough to accommodate the entire root system of the fern.

Because ferns prefer rich soil, rather than using just potting mix, fill it with a combination of all-purpose potting mix and compost. Water it well and keep the soil moist at all times. Especially when you keep your fern outdoors, you need to be diligent about watering and never let the soil dry out.

Repot the fern when it becomes root-bound, which is often indicated by smaller fronds.

Overwintering

When planted in garden soil, autumn fern does not need any protection during the winter. As a potted plant, however, its roots are not sufficiently protected from winter chills. While there is no need to bring the containers indoors, provide additional insulation around the container. You can either place the container in a larger pot or box and fill the space with mulch or sand, or wrap the sides of the container with bubble wrap, or burlap and an additional layer of plastic wrap.

Pests and Diseases

Common Pests & Plant Diseases 

Autumn fern can attract mealybugs, scales, and aphids but these are rarely a danger to the plant’s health. It is not prone to serious pests or diseases.

Common Problems 

When the fronds of autumn fern become shriveled, brown, or discolored, the cause is usually sunburn. This can happen, and rather quickly within a few hours, with new plants that have been moved to a location with too much sunlight, or plants that were grown in a greenhouse and have not been properly hardened off. It can also happen to an established fern in your yard when you prune or cut down a tree or shrub nearby that used to cast shade on the location but is now more exposed to the sun.

III. Uses and Benefits 

Autumn fern attracts gardeners due to its unusual foliage, which is the color of autumn leaves when it sprouts but turns green as it ages, instead of the other way around. It is also very tough and low-maintenance. In the garden, it is most often used in shady spots that need some color, moist areas such as beside ponds, or areas with poor soil. It is also used in mixed borders.

Autumn Fern (Dryopteris erythrosora) Details

Common name Autumn Fern, Japanese Shield Fern, Shaggy Shield Fern
Botanical name Dryopteris erythrosora
Plant type Fern
Hardiness zone 6b, 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b, 11a, 11b, 12a, 12b
Growth rate Slow
Height 1 ft. 6 in. - 2 ft. 0 in.
Width 1 ft. 6 in. - 2 ft. 0 in.
Sunlight Dappled Sunlight (Shade through upper canopy all day)
Soil condition Clay
Leaf color Gold/Yellow