The typical holly fern, Cyrtomium falcatum, is considered fairly reliable in Zone 7b, but no further north. The oddball is the coastal form, which grows on the coast of both Japan and Korea. We received the plant shown below in 2005, as Cyrtomium falcatum var. maritimum, which our taxonomy staff tells me, isn’t a valid name. According to Patrick and Zac, the Japanese coastal material is correctly called Cyrtomium falcatum var. littorale, but there is no mention in the literature they’ve reviewed of the same coastal form occurring off Korea.
Other than the dwarf size, which is often seen in plants that grow in harsh coastal conditions, these weather-battered denizens adapt by developing thicker leaves and a denser habit. Additionally, this form is significantly more winter hardy than the typical material of Cyrtomium falcatum seen in the trade. We’ve always listed this dwarf form as a Zone 7a plant, but we wouldn’t be surprised at all if it’s also hardy in Zone 6. If you’ve been adventurous enough to try it, we’d love to hear from you. Our mature clumps below, photographed over Christmas, are now 8″ tall x 18″ wide.