Frosty Fern Care: Not a Fern, Can’t Feel Dry Air Coming, and Dies Below 70% Humidity
The real reason frosty fern dies indoors: it can’t sense dry air until it’s too late. Here’s the 70% humidity fix, plus how to spot the mislabeled species.
A frosty fern looks flawless in the nursery greenhouse, gets carried home under a gift bow, and starts crisping at the tips within days. That isn’t bad luck or a black thumb. One widely read professional garden writer puts it bluntly: few people manage to keep one alive more than a month or so once it leaves that humid greenhouse for a normal heated home.
The plant isn’t fragile in the usual houseplant sense — it’s built on 400-million-year-old plumbing that simply can’t do what a pothos or snake plant does when the air turns dry. Understanding that mechanism, not just memorizing “mist it more,” is what actually keeps this one alive past the holidays.
Frosty Fern Isn’t a Fern — and It Might Not Even Be the Species on the Tag
“Frosty fern” isn’t a fern at all. It’s a spikemoss in the genus Selaginella, family Selaginellaceae — a lineage of vascular plants that split off before true ferns and long before flowering plants existed, according to North Carolina State University’s Extension Gardener Plant Toolbox. Spikemosses share a reproductive strategy with ferns (spores, not seeds), which is why the two get lumped together in casual conversation, but they’re not close relatives — a 2021 review in the peer-reviewed journal Evolution & Development puts the split between lycophytes and the rest of vascular plants at roughly 420 million years ago, older than the common ancestor ferns share with seed plants. The lacy, scale-covered stems just happen to look fern-like at a glance.
Here’s the part almost no plant tag mentions: the “frosty fern” on your windowsill probably isn’t even the species most references call Selaginella kraussiana ‘Variegata’. According to professional garden writer Larry Hodgson’s Laidback Gardener, retailers rarely use a correct botanical name on this plant at all, and the tall, upright, tufted specimen sold at Christmas — 6 to 12 inches, branching into a flattened fan shape — is usually Selaginella martensii ‘Frosty’ or ‘Variegata’ instead. True S. kraussiana ‘Variegata’ is a different growth habit entirely: a low, creeping mat rarely more than 1 to 2 inches tall that spreads sideways rather than standing up. If your plant is upright and bushy, you’re almost certainly growing martensii, whatever the tag says — and the two need nearly identical care, so it barely matters for day-to-day purposes. It matters if you’re trying to identify what you actually bought.
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UK gardeners will find true Selaginella kraussiana ‘Variegata’ listed by the Royal Horticultural Society with an Award of Garden Merit, grown under glass in bright filtered light at a minimum winter temperature of 41-45°F (5-7°C) — useful context if you’re comparing a UK plant-tag name against what a US big-box store hands you at the register, since the same common name covers genuinely different plants on either side of the Atlantic.
Why It Crashes in Dry Air When Other Houseplants Shrug It Off
Every houseplant loses water through tiny pores called stomata, and most of the plants you own can react to falling humidity before it becomes a crisis — a hormone called abscisic acid (ABA) senses the stress and tells the pores to partially close, cutting water loss ahead of real damage. Selaginella can’t do that. A 2013 study in the peer-reviewed journal New Phytologist found that ferns and lycophytes (the group Selaginella belongs to) close their stomata in direct response to their own leaf water pressure dropping, not in response to ABA signaling the way seed plants do. In plain terms: the plant has no early-warning system. Its pores don’t start closing until the tissue itself is already losing water pressure — which is another way of saying the damage has already begun by the time any defense kicks in.
That explains a pattern anyone who’s grown one will recognize: the newest growth goes first. The white, frosted tips are the youngest, thinnest tissue on the plant, with the least stored water and the most exposed surface area, so they’re the first place this slow, reactive pore closure loses the race against dry air. Once a tip crisps and browns, it stays that way — the plant can put out new white growth once conditions improve, but a damaged tip doesn’t green (or frost) back up. This is also why misting doesn’t fix the problem: a light spray raises humidity around the plant for a few minutes at most, and by the time it evaporates, the tissue is right back where it started, still waiting on a pore-closure system that was never built to react quickly in the first place.
The Real Humidity Number (and Why Misting Doesn’t Get You There)
Every source that specializes in this plant converges on the same figure: at least 70% relative humidity, sustained, not just an occasional spike. A typical heated home in winter runs closer to 30% — Hodgson’s Laidback Gardener cites that exact contrast as the reason this plant fails so consistently once furnaces kick on for the season. That’s not a small gap to close with a spray bottle.
Room humidifiers alone usually can’t get there either, at least not for a whole-room reading. Per Laidback Gardener, most household units simply aren’t built to push a whole room’s humidity anywhere near what this plant needs at leaf level — they’re sized for general comfort, not for sustaining a saturated microclimate. Getting to 70% means creating a small, enclosed pocket of air around the plant itself rather than trying to humidify an entire room.
Humidity Solutions, Ranked
Not every fix gets you to the actual target, and the honest ranking looks different depending on whether you’re a first-time buyer who just wants the plant to survive the winter, or someone already running a terrarium setup who wants this as a permanent resident.
| Method | Humidity Achieved | Best For | Trade-off |
|---|---|---|---|
| Closed terrarium or glass cloche | 85-100% (near-saturated) | Anyone who wants a true set-and-forget solution — beginners included | Needs occasional airing (10-15 minutes every few days) to prevent mold and fungal rot in that much trapped moisture |
| Grouped with other humidity-loving plants | ~50-60% around the cluster | Windowsill growers who don’t want to buy glass or equipment | Often still short of 70% through a dry winter — best paired with a pebble tray underneath |
| Wet pebble tray under the pot | ~40-55% right at foliage level | A low-cost stopgap or supplement to another method | Small evaporation surface, needs refilling every few days, rarely reaches 70% alone |
| Room humidifier only | Usually under 50% at typical room size | General house comfort, not plant-specific humidity | Almost never reaches 70% unless the humidifier is running inside a small, closed space with the plant |
The practical takeaway: a beginner who just wants this plant to make it through winter is better off spending $10-15 on a glass cloche or cake dome than on a humidifier, since the cloche gets closer to 70% for less money and no maintenance beyond opening it periodically. Someone who already keeps a closed terrarium, on the other hand, has the easiest win available — this is one of the few houseplants that genuinely does better sealed up than out in the open.
Watering, Light, Soil, and Temperature
Keep the soil constantly moist to the point of nearly wet, never fully dry between waterings — this is one of the few common houseplants where under-watering, not over-watering, is the faster way to kill it. Use room-temperature water; NC State Extension notes cold water can shock the plant outright. Ease off slightly in fall and winter dormancy, but don’t let the soil dry.
Light should be bright indirect to partial or deep shade — 2 to 6 hours of gentle light at most. Direct sun scorches the foliage fast; set one on a bare south-facing sill in full afternoon sun and by the next day the newest tips will have gone limp and translucent, faster than almost any other “easy” holiday plant sold alongside it.
Soil should run acidic to neutral, roughly pH 6.0-8.0, heavy on organic matter but still well-draining so the constant moisture doesn’t turn stagnant. Temperature should stay in the 60-80°F range; below 50°F risks cold damage, and above 80°F the plant starts to suffer just as fast as it does in dry air.
Skip regular fertilizer, or feed at half-strength no more than monthly during active growth. Nitrogen-heavy feeding is a specific, well-documented mistake here: it turns the white tips solid green, erasing the exact frosted look that makes people buy the plant in the first place.
Symptom, Cause, Fix
| Symptom | Likely Cause | Fix |
|---|---|---|
| Tips crisp and brown, starting with newest growth | Humidity below ~70% — the passive pore-closure response reacted too late | Move into a closed terrarium or under a glass cloche; add a wet pebble tray as an immediate stopgap |
| Whole fronds go soft, mushy, and dark | Standing water or overwatering causing root rot | Unpot, trim away mushy roots, repot into fresh well-draining mix, and never let the saucer hold standing water |
| White tips turn solid green | Too much nitrogen fertilizer | Stop feeding; resume only at half-strength, monthly, during active growth |
| Sparse, leggy growth with bare stem bases | Insufficient light, or old growth that’s never been trimmed | Move to brighter indirect light and trim leggy stems to force bushier new growth |
| Bleached or scorched patches on foliage | Direct sun exposure | Relocate out of direct sun into bright indirect or partial shade |
| Sudden wilting near a window or vent in winter | Cold drafts or hot, dry airflow from a heating vent | Move away from drafts and vents; keep the plant in the 60-80°F range |
| Fine webbing and dull, stippled foliage | Spider mites, which favor the same dry air that already stresses the plant | Isolate the plant, raise humidity, and treat with insecticidal soap |
Is It Safe Around Pets and Kids?
Yes. NC State Extension lists Selaginella kraussiana as non-toxic to cats, dogs, and horses, and Laidback Gardener confirms the same for children. That said, a curious pet chewing through any plant material can still cause mild stomach upset, so keeping it out of easy reach is still worth doing even without a toxicity risk behind it.
Frosty Fern vs. Cyclamen: The Other Cool-Room Holiday Plant
If frosty fern shares a shelf with cyclamen at the garden center every December, don’t assume the two want the same spot at home — they want close to opposite conditions. Cyclamen prefers cool rooms (roughly 50-65°F, cooler at night), bright light, and soil allowed to dry slightly between waterings — with water applied from below so the crown, the base where the leaves emerge, never stays wet, since a soggy crown is what actually causes cyclamen to rot. Frosty fern wants the opposite temperature and watering rhythm: warmer air and a substrate kept constantly damp, with humidity pushed as high as the setup allows. Group both in the same warm, wet cloche thinking you’re solving “holiday plant care” once for both, and the trapped heat and moisture around the crown are likely to rot the cyclamen while the frosty fern does fine. Give each its own microclimate instead.
Frequently Asked Questions
Is frosty fern a real fern?
No — it’s a spikemoss in the genus Selaginella, a separate, older lineage of spore-producing plants that’s related to ferns but not a fern itself.
Stop killing plants with wrong watering.
Select your plant, pot size, and climate zone — get a precise watering schedule with amounts and timing.
→ Build Watering ScheduleMy frosty fern already has brown tips — can it come back?
The browned tips themselves won’t turn white again, but if the roots and crown are still firm, fixing the humidity (closed terrarium or cloche) usually lets the plant push out healthy new white-tipped growth to replace what was lost.
Will it survive after the holidays are over?
Yes, as long as it keeps getting close to 70% humidity year-round — this isn’t a plant that only needs special care during the gift-giving season and can coast the rest of the year.
Frosty fern is one of several plants sold for their holiday timing rather than year-round ease — see our complete holiday plants care guide for how poinsettia, Christmas cactus, amaryllis, and cyclamen each get triggered into bloom on cue.
Sources
Selaginella kraussiana — NC State Extension Gardener Plant Toolbox
Selaginella kraussiana ‘Variegata’ — Royal Horticultural Society
McAdam, S.A.M. & Brodribb, T.J. (2013). Ancestral stomatal control results in a canalization of fern and lycophyte adaptation to drought. New Phytologist, 198(2), 429-441
Spencer, V., Nemec Venza, Z. & Harrison, C.J. (2021). What can lycophytes teach us about plant evolution and development? Evolution & Development, 23(3), 174-196
Frosted Fern: A Christmas Mystery Plant — Laidback Gardener
Frosty Fern: Not So Easy — Laidback Gardener
Selaginella Kraussiana & Selaginella Martensii – Frosty Fern Care — The Gardening Cook
Frosty Fern Information — Gardening Know How
Frosty Fern: Another New Holiday Houseplant — Horticulture Magazine
