Cystopteris fragilis
Cystopteris fragilis
Brittle bladder fern
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Taxonomy
Family Aspleniaceae · Genus Cystopteris
Description
Cystopteris fragilis, the brittle bladder fern, is a dainty, cold-hardy fern for cool, shaded nooks and rock crevices. Its finely divided, lacy fronds emerge fresh green in spring and, despite their delicate look, it’s tough when given consistent moisture, excellent drainage, and protection from hot sun. A charming choice for woodland edges, shaded stone walls, and trough gardens.
Common Names
Brittle bladder fernFragile fernCommon fragile fern
Context
nativeRegion
Circumboreal: widespread across cool-temperate North America, Europe, and Asia, often in rocky, mountainous habitats.
usdaZones
3–7 (to 8 in cool-summer or higher-elevation sites)
companionPlants
Asplenium trichomanes (maidenhair spleenwort), Asplenium ruta-muraria (wall-rue), Saxifraga paniculata, Primula spp., Heuchera spp., Mosses and small crevice plants (e.g., Campanula spp.)
culturalUses
Ornamental for shaded rock and crevice gardens, stone walls, and woodland restorations; valued for stabilizing rocky slopes and enhancing microhabitats for mosses and shade flora.
Care
Care Requirements
LightShade to dappled/bright indirect light; avoid harsh midday sun. Morning or late-afternoon sun is tolerable in cool climates.
WateringKeep evenly moist but never waterlogged. Water when the top 1–2 cm of soil feels barely dry; increase frequency during hot, dry spells.
SoilWell-drained, humus-rich, gritty mix with plenty of mineral content; excels in rocky, calcareous or neutral substrates (crevice/rock-garden style).
FertilizerLight feeder. Top-dress with leaf mold or compost in spring; optional 1/4-strength balanced fertilizer monthly in active growth.
HumidityPrefers moderate to high humidity; mulch to conserve moisture. In dry climates, group with other plants or mist lightly in heat waves.
TemperatureIdeal 40–70°F (4–21°C). Hardy to about USDA zone 3; protect from prolonged heat above ~85°F (29°C) and keep roots cool.
Growth & Life Cycle
HabitSmall, clumping rhizomatous fern with delicate, finely divided fronds.
Mature Size6–14 in tall (15–35 cm); 8–18 in spread (20–45 cm).
Growth RateModerate; faster with cool temperatures and steady moisture.
BloomingNo flowers; produces spores on the undersides of fronds, typically late spring through summer.
DormancyDeciduous in winter (dies back in cold); may go semi-dormant in heat/drought.
Propagation
MethodsDivision of clumps/rhizomes, Spores (sterile technique)
DifficultyEasy by division; advanced by spores.
Best SeasonEarly spring (division); collect spores in summer and sow late winter to early spring under sterile conditions.
Maintenance & Notes
PruningRemove damaged or spent fronds as needed; cut back old fronds in late fall or early spring to make room for new growth.
RepottingFor containers/troughs, refresh mix and divide congested clumps every 2–3 years in early spring.
Pests & DiseasesGenerally trouble-free. Slugs/snails may chew fronds; occasional aphids or scale. Avoid waterlogged soils to prevent crown/root rot and fungal leaf spots.
ToxicityNon-toxic to people and pets.
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