Cold-Hardy Tree Ferns for Temperate Gardens

Tree ferns evoke the tropics, yet many species tolerate surprising cold, allowing gardeners in Britain, the Pacific Northwest, the Mediterranean, and the southern U.S. to grow these living sculptures outdoors. They also provide shelter for tender understory plants in marginal climates.

Anatomy of a Tree Fern

Tree ferns aren't true trees. The "trunk" is a vertical mass of tightly packed rhizomes (specialized roots) that support the crown and transport water and nutrients. Fronds emerge from coiled croziers (fiddleheads) at the apex, radiating 360° like palms. Fronds divide into symmetrical leaflets along a central rachis, creating intricate lacy patterns. Reproduction is via microscopic spores formed in sori on frond undersides.

Trunks and croziers are often covered in scales or hairs—these look soft but are irritating to skin, eyes, and lungs. "Soft fern" (Dicksonia antarctica) is a misnomer.

Cultural Needs

• Cold hardiness: Relative; zones 8+ easiest, some to zone 7 with protection. No outdoor success in zones 1–5.
• Heat tolerance: Dry heat is often more damaging than cold. Keep trunks and crowns constantly moist via drip irrigation or misters.
• Light: High requirements; few tolerate full sun in hot, arid climates. In humid/cool areas, full sun is beneficial.
• Soil: Acidic, well-drained, heavily mulched. Never let roots dry out completely.
• Fertilizer: Nitrogen-rich, but sparingly—overfeeding is easy.

Major Genera in Cultivation

Cibotium (Hawaiian tree ferns): C. glaucum (slow, to 10+ ft, damaged ~28°F, hates dry heat/wind), C. schiedei (Mexican tree fern, shrubby, softer, more tolerant).

Cyathea (largest genus): C. cooperi (most common, fast, to 30 ft, damaged ~27°F; 'Brentwood' cultivar more robust), C. medullaris (NZ, to 50+ ft, black leaf bases, more cold-tolerant), plus C. brownii, C. dregei (most cold-hardy), C. dealbata, C. australis, C. princeps (beautiful but finicky), C. amaragarensis, C. spinulosa.

Dicksonia: D. antarctica (most widely grown, slow, long-lived, to 50 ft, hardy to low 20s, still needs summer crown watering), D. squarrosa (black trunk, golden hairs, pale leaf undersides, suckering, hardy to ~25°F), D. fibrosa, D. sellowiana.

Sadleria: S. cyatheoides (Hawaiian, epiphytic, ornamental tight foliage, narrow temp range).

"Short" tree ferns: Blechnum (B. gibbum 'Silver Lady', B. brasiliense red new growth, B. moorei, B. tabulare—small trunked, defoliate ~27°F) and Angiopteris (A. evecta 'Mule's foot', massive spread, needs high humidity).

For detailed protection techniques and species data, visit the Cold Hardy Tree Fern page (angelfire.com/bc/eucalyptus/treeferns).