What is a frosty fern?
Despite its name, frosty fern (Selaginella kraussiana) is not a fern at all. It is a spike-moss, a member of one of the oldest vascular plant lineages on Earth. Its fronds look uncannily like a miniature fern, but the frosted white tips on the growing edges are what earn it the “frosty” label. Native to humid, shaded forest floors in Africa and the Azores, it has been a popular terrarium and holiday-season houseplant for decades, though it has a reputation for being difficult to keep alive in dry indoor air.
How much light does a frosty fern need?
Frosty fern is a low- to medium-light plant — one of the best choices for dim spots. In its native habitat it grows under a dense forest canopy, so bright or direct sun scorches the delicate fronds quickly. A north-facing windowsill, a shelf a few feet from an east-facing window, or a spot under grow lights all work well. Too little light will cause the silvery-white tips to fade on new growth; a little more indirect light brings them back.
How often should you water a frosty fern?
This is where frosty fern earns its “difficult” reputation. It has essentially no drought tolerance — the soil should stay consistently moist at all times. Water every 3–5 days in normal indoor conditions, checking with a finger that only the very surface is beginning to dry before watering again. If the root ball dries out completely, the plant collapses alarmingly fast; to rescue it, submerge the pot in water for 10–15 minutes and then drain.
Why does humidity matter so much for frosty fern?
Frosty fern evolved in high-humidity forest environments (typically above 60% relative humidity) and struggles in the dry air of most heated or air-conditioned homes. Crispy brown frond tips are almost always a humidity problem. Solutions include setting the pot on a pebble tray filled with water (keep the pot above the water line), misting the fronds daily, grouping it with other moisture-loving plants, or growing it in a terrarium, which is arguably its ideal indoor environment.
Can you grow frosty fern in a terrarium?
Yes — and it often thrives better in a closed or semi-closed terrarium than on an open windowsill. The enclosed environment keeps humidity high and reduces the need for frequent watering. Use a well-draining terrarium mix with some orchid bark or perlite to prevent waterlogging, and ensure the terrarium gets bright, indirect light. Frosty fern’s low, spreading habit makes it an excellent ground-cover layer alongside nerve plants or mosses.
Is frosty fern safe for pets?
Yes — the ASPCA lists Selaginella kraussiana (under the common name club-moss) as non-toxic to cats and dogs. It is a safer option for pet households compared to many other popular fern-like plants.