Terrariums are enclosed plastic or glass structures for growing plants. Plants in a terrarium can often go a month or more without watering because the enclosed structure allows them to recycle the humidity produced by the plants. Terrariums must be water- and airtight, and large enough to hold the plants. Small plants with a slow growth rate are the best choice for terrariums since they require less pruning and trimming.
Fluffy duffy (Nephrolepsis exaltata) is a variety of Boston fern which grows up to 6 inches tall. The plant has overlapping, fine-textured fronds which are divided into two and three sections. The short height of the fern at maturity makes it ideal for growing in terrariums. The fern adapts well to different light levels, and thrives in warm, humid conditions with an ideal temperature of 60 to 70 degrees F. Fine-textured ferns such as fluffy duffy are especially particular about moisture so do well in terrariums. Browning of the fronds indicates a humidity level that's too low.
Begonia prismatocarpa is the smallest variety in the begonia plant family, growing to a mature height of only 5 inches. The plant is native to tropical areas, and requires tropical growing conditions of warmth and humidity. Its slow growth makes it one of the best plants for enclosed terrariums. The plant blooms with bright yellow flowers with red stripes. Amend the growing medium amply with angel moss or sphagnum moss before planting. Deadhead the faded flowers and any damaged leaves to maintain appearance.
Peacock spike moss (Selaginella uncinata) is a native Chinese selaginella variety. The semi-evergreen plant with straw-colored stems and metallic blue foliage grows to a mature height of about 6 inches with a two-foot spread. Peacock spikemoss is a low maintenance plant ideal for terrariums. It thrives in shade and moist, fertile soil. The plant is grown mainly for its foliage and does not flower. Peacock spikemoss is easy to propagate with stem cuttings. Dilute a balanced fertilizer to half its strength and use weekly for optimal growth.