Why Are My Dryopteris Fronds Curling?

Drought stress

Drought is the most common cause of dryopteris frond curl. Even though dryopteris is one of the more drought-tolerant fern genera, prolonged dry conditions still cause the frond pinnae to curl inward and the frond tips to curl downward as the plant conserves moisture. The fronds may also develop brown, papery tips in severe drought. Dryopteris planted in full sun, in shallow soil, or in the dry, rain-shadow positions beneath dense evergreen canopy is particularly susceptible. Established plants with substantial rhizomes can tolerate moderate drought better than young plants, but all dryopteris perform best with consistent moisture.

What to do

• Water dryopteris during dry periods, particularly in the first two years after planting while the rhizome is establishing. Established plants are more resilient but still benefit from supplementary irrigation in a dry summer.
• Apply a mulch of garden compost or bark around dryopteris each spring to retain soil moisture and reduce competition from weeds.
• Ensure dryopteris is not planted in the dry rain-shadow under large conifers or very dense evergreen hedges where rainfall cannot penetrate. Reposition plants in these situations to a more open shaded area where they receive natural rainfall.

Late frost damage

The unfurling croziers of dryopteris are vulnerable to late spring frost. The tightly scrolled croziers expand in spring and are frost-sensitive once they begin to uncurl: a late frost in April or May causes the expanding pinnae to curl, blacken, and collapse. The damage can look alarming but the rhizome is rarely harmed by the degree of frost typical of UK springs, and most dryopteris species produce replacement croziers within two to three weeks. Semi-evergreen species that retain old fronds through winter provide some natural protection to the crown, as the old fronds act as a frost buffer around the emerging croziers.

What to do

• Leave the old fronds of semi-evergreen dryopteris species in place through winter and early spring. They protect the crown and the emerging croziers from frost and only need to be removed when the new croziers are clearly visible and growing vigorously.
• Cover emerging croziers with horticultural fleece when hard frost is forecast in April.
• Apply a mulch of bark or garden compost around the crown in late autumn. This insulates the rhizome from hard frosts and delays crozier emergence slightly in a very cold spring.

Too much sun

Dryopteris is a shade plant and performs poorly in full, exposed sun, particularly in dry conditions. In full sun, the frond pinnae curl inward and develop bleached, scorched patches, the fresh green or copper-green colour fades to a yellowish tone, and frond size is reduced. Dryopteris filix-mas tolerates more sun than many other fern species, particularly in moist soil or in mild, overcast UK climates, but prolonged full afternoon sun in a dry position causes consistent frond damage.

What to do

• Relocate dryopteris to a shaded position under deciduous trees or on the north or east-facing side of structures. Even light dappled shade significantly reduces sun-related frond stress.
• In positions that receive morning sun, dryopteris typically performs adequately provided the soil remains moist. It is afternoon sun in combination with dry soil that causes the most damage.

Vine weevil

Vine weevil larvae feed on dryopteris rhizomes in autumn and winter, causing the fern to produce weak, curling, undersized fronds in spring as the root system is reduced. Adult vine weevils feed on the frond margins in summer, producing the characteristic scalloped notching on the pinnae edges. In gardens with high vine weevil populations, the larval damage to the rhizome can be severe enough to kill established ferns over one or two winters. Young, recently planted dryopteris with smaller rhizomes are more vulnerable than long-established plants.

What to do

• Apply biological nematode control (Steinernema kraussei) to the soil around dryopteris in early autumn when soil temperatures are between 5 and 12 degrees Celsius.
• When dividing dryopteris, examine the rhizome and surrounding soil for vine weevil larvae and remove any found. The fibrous roots of established dryopteris make thorough inspection difficult, but the outer soil layer around the rhizome is where most larvae are found.
• Hand-collect adult vine weevils from the fronds at night with a torch in late spring and early summer.

Poor soil

Dryopteris is tolerant of a wide range of soil conditions but performs best in reasonably fertile, humus-rich soil. In very poor, thin, or compacted soil, the fronds are notably smaller and may curl at the margins as the plant lacks the resources to maintain healthy foliage. Dryopteris filix-mas is the most tolerant of poor soil among the commonly grown species, but even this robust native benefits from organic matter enrichment.

What to do

• Incorporate garden compost or leafmould into the planting site before establishing dryopteris.
• Top-dress around established plants each spring with a layer of garden compost to improve soil fertility and structure progressively over time.
• Avoid planting dryopteris in heavily compacted or waterlogged clay without first improving the drainage and structure with coarse organic matter and grit.

Frequently asked questions

Why are my dryopteris fronds curling?

Dryopteris fronds curl most often from drought stress or late spring frost damage. Drought causes the frond pinnae to curl inward along their length and the frond tips to curl downward as the plant reduces water loss. Frost damages the unfurling croziers in spring, causing them to curl, blacken, and collapse. Both problems are common in UK gardens, though dryopteris is generally one of the most robust and drought-tolerant of all garden ferns compared to more moisture-demanding species.

Is dryopteris (male fern) evergreen?

Several dryopteris species are semi-evergreen or evergreen in mild UK winters, retaining their fronds through winter and only dying back in harsh frost. Dryopteris filix-mas, the common male fern, is semi-evergreen and typically retains its old fronds until the new croziers push them aside in spring. Dryopteris erythrosora, the autumn fern, is also semi-evergreen and produces striking copper-red new fronds in spring. Dryopteris affinis, the golden-scaled male fern, is similarly semi-evergreen. In severe winters all dryopteris species may lose their fronds.

What conditions does dryopteris need?

Dryopteris thrives in moist, humus-rich, well-drained to moderately moisture-retentive soil in dappled shade, partial shade, or full shade. It is one of the most versatile and drought-tolerant of all UK garden ferns and will grow in heavier shade and drier conditions than many other fern genera, though it performs best with consistent moisture. Dryopteris filix-mas, the native male fern, is particularly robust and will naturalise in dry woodland and hedgerow conditions that would not suit most other ferns.

Should I cut back dryopteris in spring?

Cut back the old fronds of dryopteris in late February or early March, just before the new croziers begin to emerge. Use gloves and scissors or secateurs to remove the old fronds at the base. Removing the old fronds before the new ones emerge gives the new croziers space and light, keeps the plant looking fresh, and removes any overwintering pests or fungal spores from the old foliage. Leave the old fronds through winter as they provide some frost protection to the crown and shelter for overwintering insects.