Cyathea medullaris
Cyathea medullaris
Black Tree Fern
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Taxonomy
Family Cyatheaceae · Genus Cyathea
Description
Cyathea medullaris, the Black Tree Fern (mamaku), is a dramatic statement plant with a jet‑black trunk and huge, arching fronds. Thriving in humid, sheltered shade, it brings a lush, prehistoric vibe to subtropical and coastal gardens.
Common Names
Black Tree FernMamakuNew Zealand Tree Fern
Context
nativeRegion
New Zealand (Aotearoa; North, South, and Chatham Islands) and parts of the southwest Pacific.
usdaZones
10–11 (9b with protection)
companionPlants
Dicksonia antarctica, Blechnum spicant, Asplenium nidus, Fatsia japonica, Hosta spp., Hedychium spp., Gunnera manicata
culturalUses
Known as mamaku in Māori; historically the inner pith was used as emergency food and for traditional remedies. Widely used ornamentally in subtropical and coastal gardens.
Care
Care Requirements
LightBright, filtered light to full shade; avoid harsh afternoon sun and shelter from wind.
WateringKeep evenly moist—never dry out. Water the crown and root zone regularly; use rainwater where possible.
SoilRich, humus-heavy, moisture-retentive yet free-draining mix; slightly acidic to neutral (approx. pH 5.5–6.5).
FertilizerLight, regular feeding in spring–summer with diluted balanced or organic fertilizer; occasional seaweed feed into the crown.
HumidityHigh humidity (60–80%+). Mist the crown, group plants, or use a humidifier.
TemperatureIdeal 60–80°F (16–27°C). Protect from frost; brief dips near 32°F/0°C may burn fronds but protect the crown.
Growth & Life Cycle
HabitEvergreen arborescent fern with a solitary black trunk and a broad, arching crown of fronds.
Mature SizeTrunk 20–50 ft (6–15 m) tall; fronds 8–16 ft (2.5–5 m) long.
Growth RateModerate to fast in warm, moist climates (about 6–12 in/15–30 cm of trunk per year).
BloomingFerns do not bloom; reproduces by spores (sori) on frond undersides, mainly in warm months.
DormancyEvergreen in frost-free climates; may defoliate in cold or dry spells and refoliate in spring.
Propagation
MethodsSpores, Tissue culture, Re-rooting established trunks/stumps
DifficultyChallenging
Best SeasonSpring to early summer, when warmth and humidity are reliable.
Maintenance & Notes
PruningRemove dead or damaged fronds cleanly at the base; never cut into the crown/apex. Maintain a mulch layer to keep roots cool and moist.
RepottingIf container-grown, move to a deeper, heavier pot every 2–3 years with a coarse, humus-rich, moisture-retentive mix. Keep the crown at the same level.
Pests & DiseasesScale, mealybugs, and spider mites (especially indoors); snails/slugs chew fronds. Crown or root rot in waterlogged soils; frond scorch from sun or wind.
ToxicityGenerally considered non-toxic to people and pets; fibrous trunk and scales may irritate skin—wear gloves.
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