Caring For And Propagating Frosty Fern

To successfully grow a frosty fern (AKA Selaginella kraussiana ‘Variegata’) you have to provide a similar environment to how it grows in its natural habitat.  It needs moist, well-drained soil, deep shade, temperatures between 68 to 84 degrees, and 77 to 88 percent humidity (please, no misting!).  Most of these requirement make for a recipe in disaster for a frosty fern inside the average household. The “secret” to successfully growing frosty fern is to treat it like the tropical rainforest plant it is.

Frosty Fern’s Native Habitat

Selaginella kraussiana grows in the lowland tropical evergreen forests in Angola, Bioko, Burundi, Cameroon, Congo, DRC, Equatorial Guinea, Ethiopia, Kenya, Mozambique, Malawi, Rwanda, Sierra Leon, Zimbabwe, Eswatini, South Africa, Sudan, Tanzania, and Uganda.  It has also become naturalized in many other tropical regions with comparable environments.

Tropical evergreen forests (AKA rainforests) have dense tree canopies with very little sunlight ever reaching the ground, except when different trees alternately shed their leaves, which allows filtered light to reach the forest floor.  These forests receive 78 to 103 inches of rainfall each year, compared to the US which only receives an average of 32 inches of rain each year.  The temperature in the rainforest stays between 68 to to 84 degrees year round and the humidity level averages between 77 to 88 percent.

Selaginella kraussiana can grow into a dense mat on the forest floor where a break in the tree canopy from above increases the intensity of light filtering downward.  In deep shade, frosty fern grows in a slightly more sparse, scattered pattern.

Frost Fern’s Growing Habit

Frosty fern is actually more of a moss than a fern, and is commonly also referred to as spike moss or clubmoss.  Its scaled leaves resemble conifer leaves.  It can grow 4 to 12 inches in height.  Its active growing season is mid to late summer, with the correct environment it actively grows year round.

The root system is fairly shallow.  Like most mosses, it prefers to grow in dense masses and spreads out as soil conditions, moisture and light allows.  The fern’s creeping habits are facilitated by dropping aerial roots from the stem of its leaves at the point where the leaf branches into two leaves.

These aerial roots are called rhizophores and have a structure more similar to a stem than a root (they have a protective coating while they are above ground).  Their growth is triggered (by auxin signaling) when the leaf branches.  They can provide support to terrestrial leaves, facilitate creeping, and will eventually branch out upon reaching the soil.  The portion that grows beneath the soil eventually becomes true roots.

Why Does Everyone Sell Frosty Fern During The Holidays?

Frosty fern’s white tipped edges are reminiscent of snow and make for great impulse buys during the holiday season.  Greenhouses start frosty fern production in July, just after the last of their spring annuals have been shipped out.  In a commercial greenhouse environment, frosty fern is easy and inexpensive to propagate and grow.  Temperatures are reduced to below 65 degrees to encourage the plant’s new growth tips to turn white.

 

How To Care For Frosty Fern

Now that we know how frosty fern grows in its native habitat,  we need to replicate that in order to grow it in our homes.  Here are a few quick “Do” and “Do Not” items to keep it happy and alive, with further explanation below.

The easiest way to tell if your healthy frosty fern is happy is if it is actively growing.  The plant has a spreading growth habit and in the ideal environment it will keep trying to spread out.  The greener leaves on the outside perimeter of the plant will begin growing outward (somewhat horizontally), seeking out soil.  By watering from below and providing a humidifier or terrarium, you’ll see your plant spread outward by at least a 1/4 inch each week.

Do

• Keep the soil evenly moist
• Water from below using a saucer or DIY capillary mat
• Keep temperatures above 68 degrees
• Keep humidity above 70 percent
• Keep the plant in low filtered sunlight
• Fertilize it once a month with orchid fertilizer or diluted seaweed extract
• Keep it out of drafts

Do Not

• Mist the plant
• Water from the top
• Let the plant dry out
• Keep out in the open or in drafts
• Keep within 2 feet of a south facing window

So How Do I Provide The Right Humidity?

Humidity is measured by the amount of water vapor (not droplets) lingering in the air;  water vapor is the gaseous vapor form of water that isn’t visible to the human eye.  Humidity reduces the rate of a plant’s moisture evaporation.  At 70% humidity, plant leaves will not feel wet or have visible water build up on its leaves.  At 80%, you might feel a thin, light film of moisture but likely not much.  If moisture does build up, you are either providing too much humidity or the temperature is below 70 degrees.

In contrast to humidity, misting provides mostly large water droplets that quickly drop onto surfaces.   Some of the finer droplets might linger temporarily in the air, slightly raising the humidity levels but only for a short period of time (10-15 minutes).  The droplets sit on plant leaves until they either evaporate or are absorbed.  If they sit on the leaves too long, the droplets interfere with a plant’s transpiration and may contribute to bacterial or fungal growth.

Putting your plant on a tray of gravel and water isn’t going to be enough if your home has low humidity, especially if indoor temperatures are low.  And misting with a spray bottle will just saturate and eventually drown your plant, causing it to get droopy.

For a frosty fern, you are shooting for at least 70% humidity.   Depending on where you live, your house is probably around 40 to 60 percent humidity.

If your frosty fern is happy, it can grow to be up to 12 inches tall, which would quickly make it too big for a standard terrarium.  There are a few options.  Keep your plant covered in a glass cloche or dome; these pop up at Goodwill stores regularly.  Or set it up so that at least 25% of the plant is inside a protected enclosure like a ceramic planter lined with gravel.  Line a deep ceramic planter or glass bowl with a drip tray and gravel or rocks and sit your plant inside with 75% of the foliage sticking out in a location with no drafts.  A humidifier or enclosing the plant to keep the plant and soil moist are the best ways to maintain the right humidity level.

The easiest option to providing optimal humidity is to pick up an inexpensive portable humidifier (like the one used in the photo above) and set it up a foot away from your plant.

If Your Frosty Fern Starts Doing Poorly Shortly After Purchasing It

Frosty ferns are sent to stores throughout the holiday season, with the last of the orders typically being filled the last week of December.  There are a few things that are out of your control, with the most important factor being how long it sat in a store before you purchased it.    Frosty ferns will tolerate some less than ideal conditions for a week or two before symptoms of the neglect begin to appear.

Let’s say you purchased your plant in mid-January; there’s a chance the frosty fern has been sitting in the store since late December.  The tell-tale sign that the plant’s deterioration is due to the time it spent at the store is if your frosty fern suddenly begins to look limp and its white tips become yellow or are browning shortly after buying it.  That’s a clear sign that the plant has not received enough water and humidity.

If Your Frosty Fern Is Green But Wilting

If your frosty fern is droopy and its leaves look dark green (darker than they did before they started drooping) and heavy, it is either developing root rot and/o r it’s leaves are holding too much moisture.   It’s roots or it’s leaves are over-saturated and unable to effectively move water and nutrients through its cells or transpire the excess moisture.  Maybe the soil is too wet and/or you are misting it with a spray bottle and temperatures aren’t high enough to effectively evaporate the water droplets.  Plants transpire (release moisture) through their leaves.  Only water from the bottom up and don’t spray water on the leaves.  This problem is more common when temperatures are cooler or near a cold window, which frosty fern does not like.

If You’ve Over Fertilized Your Frosty Fern

Frosty ferns require very little fertilizer (about once a month), and should be fertilized with a diluted low nitrogen solution.  We prefer seaweed extract.

If you use a standard plant fertilizer, part or all of your frosty fern might experience root burn.  This is usually the cause if you notice leaves that appear to be dying within a few days to a week after fertilizing.

If any part of the plant is alive, you might want to give the plant a serious drenching to try to leach out the fertilizer.  If you used a slow release fertilizer, consider repotting the surviving portion of the plant in a fresh peat/compost mix.

If Entire Branches Of Leaves On Your Frosty Fern Are Shriveling And Browning

In this photo, you can see entire branches of leaves have become pale and many of the green leaves look shriveled.   This plant has received too much sunlight and not enough waterings to compensate for moisture evaporation.  Humidity is also missing, but its primary demise is due to not keeping the soil moist at all times and reducing exposure to sunlight.

If Your Frosty Fern Tips Are Turning Brown

If the tips of your frosty fern are turning brown but you’ve kept the soil moist, then it’s likely due to too low of a humidity level.

If you’ve missed a few waterings and the soil dried out too much, sit the plant in a shallow bowl of water for an hour or so until the soil seems saturated then let it drain completely.  Trim off any brown leaves.  Water it from the bottom with a drip tray or use a capillary mat.   Cover with a plastic ziplock or glass cloche until new growth returns, then follow humidity instructions above.

My Frosty Fern Is Healthy But Is Turning Green

That’s okay.   The loss of the white tips means that the temperatures are ideal and the plant is getting enough sunlight.  Frosty Fern, in its natural habitat, is normally all green.  Not until temperatures drop and sunlight is reduced do they get that characteristic frosty tip.

How To Revive A Sad Frosty Fern

It might be possible to breathe life back into a frosty fern that is doing poorly once you figure out and correct what went wrong.  If your plant has a few remaining leaves that look healthy, trim off all the rest and make sure the surviving parts of the plant receive the proper environment (moist soil, temps, humidity, etc).  Even if none of the leaves look good, it can’t hurt to give the plant one more chance to bounce back.  If any of the rhizophores have rooted into the soil, there’s a chance they might send up crown leaves once conditions improve.

Seaweed extract is often used as a growth hormone and is said to be very effective at treating transplant shock and nursing plants back to health.

How To Propagate Frosty Fern

Because it is more like a moss and has a shallow root system, you can divide the plant into your preferred size and pot the divisions up in a peat/compost mix.  You can also take leaf cuttings about an inch below where a rhizophore appears (usually where the leaf begins to branch).  Like divisions, place the cutting with the rhizophore in a peat/compost mix and cover with plastic to retain humidity until the cutting roots up.  Humidity is such a big factor in frosty fern success, and it’s even more important when you are potting up divisions or cuttings.

Sources:

https://www.britannica.com/science/tropical-rainforest#:~:text=Mean%20temperatures%20in%20tropical%20rainforest,metres%20(328%20feet)%20climbed.

https://www.zimbabweflora.co.zw/speciesdata/species.php?species_id=100140&ishow_id=1

https://sciencing.com/characteristics-humid-tropical-climate-8520547.html#:~:text=Rainforests%20receive%20approximately%20103%20inches,and%2088%20percent%20every%20day.

https://www.ncdc.noaa.gov/sotc/national/201713#:~:text=The%20contiguous%20U.S.%20average%20annual,year%20with%20above%2Daverage%20precipitation.

https://en.wikipedia.org/wiki/Evergreen_forest

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.15630

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