Korean rock fern

Korean rock fern: how do you recognise it?

Habit

Compact, dense little clump 20–30 cm tall and wide, slow-growing.

Fronds

Glossy dark green, leathery, finely divided into small leaflets; stays green in mild winters.

Spores

Ferns do not flower: the spores sit in small groups on the underside of the fronds.

New fronds

In spring the new fronds unroll like a crozier; they are soft and vulnerable then.

Roots

A short rhizome with fibrous roots; the plant grows slowly.

Plants: March–May and September–October · Pruning: March

Why grow it?

• A small, neat fern with glossy dark green fronds that look good all year.
• Evergreen in mild winters: an ornament for the cold months.
• Compact and calm: suits a rock garden, a trough, the foot of a wall or a shady corner.
• Little work: no pruning, no feeding, hardly any diseases.
• Also suitable in a pot in a cool, bright room or a small frost-free greenhouse.

Korean rock fern: where does it grow best?

• Part shade to shade; in full sun the fronds scorch.
• Free-draining, humus-rich soil: sand or loam, acid to neutral; in a rockery between stones.
• Sheltered from cold, dry winter wind.
• Allow 25–30 cm of space per plant; in a pot, one plant or a few close together.

Light

Partial shade and shade

Soil type

Sand or loam

Acidity

Acid or neutral

Moisture

Normal

Size

0.3 m tall, 0.3 m wide

Hardiness

Hardy (to -15 °C)

Goes well with

• Small hosta: Soft leaves in the same part shade.
• Hardy cyclamen: Flowers in late summer and autumn beneath the fern.
• Barrenwort: A carpet of leaves and small flowers in spring.
• Primrose: Cheerful spring flowers in the same shade.

Korean rock fern: when and how to plant it?

Plant in March–May and September–October.

1. Plant in March–May or September–October, when the soil is neither frozen nor waterlogged.
2. Dig a hole twice as wide as the root ball and mix in leaf mould and a little sharp sand for drainage.
3. Set the plant at the same depth as in its pot, with the crown at soil level: do not bury the growing points.
4. Firm the soil and water in generously straight away.
5. Spread a thin layer of leaf mould around the base and keep the soil moist in the first year. In a pot, use a free-draining potting compost and provide drainage at the bottom.

Care

Water

Keep the soil slightly moist, but never wet. In dry weather water, especially in the first year and in pots.

Feeding

A thin layer of compost or leaf mould in spring is enough; in a pot, a little liquid feed in summer.

Mulching

A thin layer of leaf mould keeps the soil cool and moist; do not cover the crown.

Tidying

In March cut off brown or damaged fronds; leave healthy green ones.

Repotting

Repot a potted plant in spring when the pot is too full, into a slightly larger pot with fresh, free-draining compost.

Tip: Plant it in a sheltered, free-draining spot between stones and give it a blanket of leaves in hard winters: it will look good for years.

Korean rock fern: when to prune it?

Pruning months: March.

When: In March, before the new fronds unroll. Real pruning is not needed.

How:

• Cut brown and damaged fronds off at the base with sharp secateurs.
• Leave healthy green fronds; they protect the crown in winter.
• Take care of the young, rolled-up shoots in the middle of the clump.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In spring, carefully separate a clump with several crowns using a sharp knife or spade and replant at once. The plant grows slowly; only divide it if necessary.

Spores

Possible but slow and a test of patience: scatter ripe spores on damp seed compost, cover with glass or plastic and wait for months.

Korean rock fern: how does it get through the winter?

Hardy to −15 °C: protect young plants.

• Hardy down to about −15 °C: in sheltered gardens in Flanders usually without protection, but in hard winters add a layer of leaves or conifer branches.
• The fronds stay green in mild winters and may turn brown after hard frosts; cut them off in March.
• In a pot it is more vulnerable: stand it against a sheltered wall and wrap the pot in hessian, or move it into a cool, frost-free, bright place.

Diseases and pests

• Winter damage: Brown fronds after hard frost or cold wind. Cut them off in March and cover the crown with leaves in hard winters.
• Drought: Brown, shrivelled leaf edges from too little water. Water and mulch the soil.
• Wet feet: In heavy, wet soil the crown rots in winter. Plant in a well-drained spot or work in compost and sharp sand.
• Slugs: Young, soft fronds are nibbled in spring. Look for them in the evening and remove them by hand.

Through the year

• March: Cut off damaged fronds. Apply compost. Plant.
• April: New fronds unroll. Plant.
• May: Plant. Water in dry spells.
• June: Water in dry spells.
• July: Water in dry spells.
• August: Water in dry spells.
• September: Plant.
• October: Plant. Thin layer of leaf mould.
• December: Rest. In hard frost cover the crown with leaves or conifer branches.

Did you know?

• The species name tsus-simense refers to the island of Tsushima between Korea and Japan.
• The name Polystichum means ‘many rows’ and refers to the rows of spore clusters on the underside of the fronds.
• This small fern is also often grown as a houseplant or in a terrarium in a cool, bright room.