Troubleshooting
Sea Spleenwort problems — and how to fix them
Sea Spleenwort (Asplenium marinum) is generally low-drama, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Frost damage
The most serious risk outside mild coastal gardens. Fronds blacken rapidly below -3 °C. In the UK, only reliably hardy in USDA zone 8+ gardens (Scilly Isles, far south-west Cornwall, western Ireland). Elsewhere, overwinter under glass.
Low humidity browning
Frond tips and margins turn brown when indoor humidity falls below about 50 % (common in heated homes in winter). Daily misting and a humidity tray are essential; group with other moisture-loving plants.
Prevent sea spleenwort problems before they start
Most sea spleenwort issues are care-mismatch, not bad luck. Dial in the basics:
Sea Spleenwort problems — FAQ
Why is my sea spleenwort frost damage?
The most serious risk outside mild coastal gardens. Fronds blacken rapidly below -3 °C. In the UK, only reliably hardy in USDA zone 8+ gardens (Scilly Isles, far south-west Cornwall, western Ireland). Elsewhere, overwinter under glass.
Why is my sea spleenwort low humidity browning?
Frond tips and margins turn brown when indoor humidity falls below about 50 % (common in heated homes in winter). Daily misting and a humidity tray are essential; group with other moisture-loving plants.