The survival of a fern in winter depends entirely on its specific species and natural habitat. Ferns are diverse, non-flowering plants that reproduce via spores, and their cold tolerance varies widely. Whether a fern “dies” is often a matter of perception; some merely shed their visible growth, while others perish completely upon exposure to frost.
Defining Hardiness: Hardy vs. Tender Ferns
The fate of a fern in winter is determined by its classification as either hardy or tender. Hardy ferns originate in temperate zones and are genetically equipped to endure freezing conditions. They tolerate cold temperatures by entering a resting state, allowing them to survive the winter outdoors. Examples include the Christmas Fern (Polystichum acrostichoides) and the Japanese Painted Fern (Athyrium niponicum ‘Pictum’).
Tender, or tropical, ferns evolved in consistently warm climates and cannot withstand freezing temperatures or prolonged cold. These varieties are often sold as seasonal outdoor plants or year-round houseplants and will quickly perish if subjected to frost. Common examples needing protection are the Boston Fern (Nephrolepis exaltata) and the Maidenhair Fern (Adiantum species).
The Biology of Winter Survival: Dormancy
Hardy ferns survive winter by engaging in a natural biological process called dormancy. When temperatures fall and daylight hours shorten, the plant significantly slows its metabolic functions to conserve energy. This response is similar to hibernation, allowing the fern to weather unfavorable conditions.
The visible fronds often turn brown and wither away, which can mistakenly signal the plant’s demise. However, energy is securely stored in underground structures known as rhizomes. These rhizomes are horizontal stems that store starches and sugars to fuel the next season’s growth. The soil and the insulating layer of dead fronds protect the rhizomes and the underground crown until spring returns.
Practical Steps for Winter Protection
For hardy ferns planted in the garden, the best practice is to leave the spent fronds in place through the winter. These withered fronds form an insulating blanket that protects the crown and rhizomes from temperature fluctuations. If a tidier appearance is desired, wait until late winter or early spring to remove the old foliage, right before new growth emerges.
Applying a loose layer of winter mulch, such as shredded leaves or straw, around the base provides additional insulation, especially in regions with severe cold. This mulch helps keep the soil temperature stable, shielding the rhizomes from harsh freezing. Ensure the crown is not completely buried under a heavy accumulation of leaves, as this can trap too much moisture and cause rot.
Tender ferns, especially those in containers, must be brought indoors before the first expected frost. Once inside, these plants require bright, indirect light, such as near an east or north-facing window, and protection from cold drafts. Central heating systems drastically reduce indoor humidity, so a pebble tray or humidifier is often necessary to maintain the moist conditions tropical ferns need. During winter, reduce watering, allowing the top layer of soil to dry slightly between waterings. Fertilizer should be withheld until active growth resumes in spring.