Rustyback

Rustyback: how do you recognise it?

Habit

Small rosette-forming tuft 5–15 cm tall and 10–20 cm across.

Fronds

Leathery and deeply cut into alternate, rounded lobes; upper side matt dark green.

Underside

Densely covered with scales, silvery at first, later rusty brown; they slow drying out and cover the spore clusters.

Drought

In dry weather the frond curls inwards; after rain it unrolls and turns green again.

Roots

Fine roots that creep deep into joints and crevices.

Plants: March–May and September–October

Why grow it?

• One of the few ferns for a sunny, dry spot: ideal for walls, rock gardens and troughs.
• Evergreen: a lively, leathery little rosette all year round.
• Fascinating to watch: in drought the fronds curl up to show their rusty scales, then unroll after rain.
• A native species that suits a natural wall or rock garden.
• Needs hardly any care once settled: no feeding and no pruning.

Rustyback: where does it grow best?

• Sun to partial shade; it tolerates more sun than almost any other fern.
• A crevice in a wall or between stones, filled with a lean, limy mix of coarse sand, a little loam and limestone chippings or old lime mortar.
• Dry and very free-draining: standing water around the roots is fatal.
• No rich garden soil and no thick mulch: in an ordinary border it soon disappears.
• One plant per crevice, or 15–20 cm apart in a rock garden.

Light

Sun and partial shade

Soil type

Sand or loam

Acidity

Chalky

Moisture

Dry

Size

0.15 m tall, 0.2 m wide

Hardiness

Hardy (to -25 °C)

Goes well with

• Ivy-leaved toadflax: Creeps through the same joints with small lilac flowers.
• Maidenhair spleenwort: Another small wall fern, for the shadier side of the wall.
• Biting stonecrop: Small yellow flowers in June in the same sunny, dry spot.
• Houseleek: Evergreen rosettes that need just as little water and food.
• Thyme: Fragrant, flowering cushions for the edge of the rock garden.

Rustyback: when and how to plant it?

Plant in March–May and September–October.

1. Plant from March to May or in September–October, ideally during a damp spell.
2. Choose a young plant in a small pot: large, old plants are slow to establish.
3. Clear out a crevice between the stones a little and fill it with a mix of coarse sand, a little compost and limestone chippings or old mortar.
4. Slide the root ball in, with the crown of the plant just at the outer edge of the crevice, and firm the mix well; a small stone holds it in place.
5. Water gently with a fine rose and keep the plant slightly moist for the first few weeks until it has rooted.

Care

Water

Only for the first few months in dry spells. After that, not at all: fronds curled up in drought are normal and not a sign of distress.

Feeding

Not needed and even harmful: it prefers poor soil.

Weeding

Remove moss, grass and weeds that smother the plant, but pull gently so as not to tear out the roots.

Wall care

When repointing or cleaning an old wall, spare the joints where ferns grow: pressure washing and new, hard cement joints make it disappear.

In a trough

A lean, limy, very free-draining mix, and not too wet in winter.

Tip: Plant it in a sunny crevice of an old wall with lime mortar and then give it nothing more: no fertiliser and no extra water. Lean and dry is exactly what it wants.

Rustyback: when to prune it?

When: Not needed: rustyback is not pruned.

How:

• At most, pick off the occasional completely withered, brown frond.
• Curled-up fronds are not dead: do not cut them off, they unroll again after rain.

Caution: Do not mistake curled fronds in a dry summer for a dead plant: wait for a shower of rain first.

Pruning calendar and basic rules

Propagation

Spores

In summer, let a frond with ripe spores dry on a sheet of paper and sow the spores on a sterile, limy seed mix under glass. It takes a year or more before the young plants are large enough to plant out.

Division

Older clumps with several crowns can be carefully pulled in two in spring, but this does not always succeed.

Rustyback: how does it get through the winter?

Hardy to −25 °C.

• Hardy to about −25 °C: no protection needed in Belgium.
• Wet roots are more dangerous than frost in winter: make sure water drains away quickly.
• In a trough or pot: move it under cover or against a wall in winter, so it does not sit in the rain.

Diseases and pests

• Rotting: Browning crown and soft fronds in wet soil or too much shade. Replant in a drier, freer-draining mix in a sunnier place.
• Smothered by moss: In a damp, shady corner, moss and algae grow over the plant. Remove them gently; a sunnier spot helps.
• Fading away: In rich garden soil or among vigorous plants it disappears. Choose a lean wall crevice or rock garden.
• Curled fronds: Not a problem but a survival trick in drought: after rain the fronds unroll again.

Through the year

• March: Remove moss and weeds around the plant.
• April: Plant in a wall crevice or rock garden.
• May: Plant. Keep young plants slightly moist.
• July: In drought the fronds curl up: no cause for alarm.
• August: Collect ripe spores.
• September: Plant during a damp spell.
• October: Plant. After the autumn rain the fronds are nicely green again.
• December: Rest. The fronds stay green.

Did you know?

• It is a resurrection plant: it can dry out severely without dying and recovers after rain.
• Its former name, Ceterach officinarum, refers to the apothecary’s workshop (‘officina’): the plant was once sold by apothecaries.
• The scales on the underside of the frond slow evaporation and cover the spore clusters.