Variegated spike moss (Selaginella martensii ‘Variegata’), sold under the name Frosty Fern. Photo: http://www.harster.ca
Question: I received a small fern for Christmas with the name Frosty Fern. I’d like to know if it’s easy to grow. Also, all around the plant there are thin leafless stems, like stilts, and they aren’t very attractive. Can I remove them?
Answer: Actually, the Frosty Fern really isn’t a fern. It’s a Selaginella or spikemoss: more specifically Selaginella martensii ‘Variegata’. Spikemosses are primitive plants that are neither ferns nor mosses, but something in between. “Frosty Fern” is actually a recent trademark chosen by a merchant to stimulate sales. A more accurate name would be variegated spikemoss.
This plant often sold at Christmas because, with its arched stems covered with green scales and white variegated tips, it looks somewhat like a mini conifer dotted with snow.
Not Easy to Grow
And no, I certainly wouldn’t say that variegated spikemoss is easy to grow. In fact, few people manage keep it alive more than a month or so. That’s because it needs conditions that aren’t easy to maintain in the average home.
The most important thing to understand is that needs very high humidity: 70% or more. Since the average home barely makes it to 30% humidity in winter, it’s in trouble from the moment you bring it home.
Ideally, you’d grow it inside terrarium, preferably one with a cover, precisely because the air there is very humid. To keep it going on a dining room table or windowsill, increase the humidity by using a humidifier and place it on a humidity tray.
Don’t bother spraying with tepid water, a technique once recommended to increase humidity. Spraying simply doesn’t raise the humidity enough to make any difference whatsoever and is a total waste of time.
Also, it prefers that its soil always remain moist, even wet, a stark contrast with most indoor plants: you’d normally allow them to dry out a bit before watering. The best thing to do for this plant is to always leave the pot soaking in a saucer of water.
Other than that, variegated spike moss is fairly easy to keep going. For example, it will grow in shade or partial shade, even sun (as long as you keep it moist). So, any bright spot, even without any direct sun, would do.
Ditto for temperature: if you’re comfortable, your plant will also be comfortable. On the other hand, in summer, when temperatures range well above 21 ˚C, it may temporarily lose its white variegation and become entirely green. If so, don’t worry: its two-tone coloring will return when fall brings cooler temperatures.
Finally, don’t overfertilize this plant. Fertilizer too rich in nitrogen (the 1st number of the 3 on the label) can also make it turn green. So, either avoid fertilizer or fertilize only very lightly and infrequently.
The thin stems that intrigued you, reminding you of stilts, are actually aerial roots. They descend from arched stems and take root in the soil below. This allows the plant to expand outwards over time. In nature, spikemoss is a ground cover, forming a green carpet in its natural environment, the tropical forests of Central America. If the presence of aerial roots bothers you, yes, you certainly can just clip them off.
Best of luck with this Christmas plant! With proper care, you can keep it alive and thriving throughout the year. Just don’t treat it like an average houseplant.