Botanical Name: Selaginella kraussiana and other spp.
I'll just say it up front. Clubmoss requires high humidity, so unless you live in the tropics, you'll want to boost the humidity around this plant to keep it lush and green.
Its mounding habit is made up of creeping stems that spread quickly across the soil, forming a dense mat of foliage. Selaginella adds a wonderful texture to any plant grouping. Its unusual, branching foliage gives it another common name, Spike Moss.
Many types of Selaginella are available for sale. Variegated and gold varieties will add beautiful contrast to your collection.
Golden-green Selaginella kraussiana 'Aurea' is a popular cultivar. 'Variegata' has creamy white tips, giving it the common name, Frosty Fern. Tiny-leafed 'Brownii' forms a tight mass that spreads out, rather than up.
Prune it back in spring to keep this spreading plant under control. You can prune up to half of the plant, if you want. It's a vigorous grower and will fill out again. Don't toss out those stem cuttings, either -- they root easily for more plants.
Repot in spring when it outgrows its pot. Clubmoss has shallow roots, so a shallow pot will do. Use a pot with a drainage hole to prevent soggy soil, which will lead to root rot. Want to use a decorative pot without drainage holes? Use it as a cachepot. Just slip a plain nursery pot into the cachepot. I put small rocks in the bottom of cachepots to keep the inner pot above the drainage water.
Is Selaginella poisonous? No -- it's safe around cats and dogs.
Origin: South Africa
Height: Spreads out rather than up. You can keep any variety small by pruning it back.
Light: Moderate light. Keep it out of direct sunlight, which can scorch foliage.
Water: Aim to keep the potting medium lightly moist at all times, but don't allow the plant to sit in water. It's a good idea to use a pot with a drainage hole to prevent root rot. Remember to always use room-temperature water for your tropical houseplants because cold water is a shock to them.
Humidity: High -- above 50% relative humidity. Indoor air can become extremely dry during the winter months. Use a humidity monitor, rather than guess -- it's the only sure way to know whether the air is too dry for your houseplants. If the air is dry, mist the plant every morning with room-temperature water or stand the pot on a tray of wet pebbles. Keep clubmoss in a terrarium to maintain humidity around it, near a cool-mist room humidifier or in a Wardian case.
Temperature: Average room temperatures (65-75°F/18-24°C). Try to maintain a steady temp -- Selaginella doesn't like it too cold or too hot, especially drafts. Keep this plant away from entryways and heat/AC vents.
Soil: Peat moss-based potting mix with perlite or horticultural sand added for good drainage.
Fertilizer: Selaginella is not a heavy feeder. Feed monthly spring through fall with a balanced (such as 10-10-10 NPK) liquid fertilizer, at half strength. Add fertilizer while watering to prevent burning the roots.
Propagation: Division or stem cuttings. Take stem tip cuttings in spring or summer. Just give the stems contact with the soil and they'll take root as they grow, forming a spreading mat.