Whether ferns survive the winter depends entirely on the specific type of fern and the climate where it is growing. Ferns are ancient vascular plants that reproduce via spores, and their cold-weather tolerance is not universal. Their survival strategies range from species that thrive under snow to those that perish at the first frost. Understanding these survival mechanisms and categories is necessary for appreciating how these diverse plants manage the colder months.
Categorizing Ferns by Cold Hardiness
Fern species can be grouped into three main categories based on their winter tolerance, which determines their ability to “live” through the cold season. The first group includes hardy, deciduous ferns that are well-adapted to temperate climates and severe winters. These ferns, such as the sensitive fern (Onoclea sensibilis) and the ostrich fern (Matteuccia struthiopteris), appear to die completely when temperatures drop. Their fronds turn brown and collapse, but the living structure, the rhizome, remains viable beneath the soil surface.
The second category is that of evergreen ferns, which retain their green fronds throughout the winter, provided temperatures are not excessively low. The Christmas fern (Polystichum acrostichoides) is a common example, often appearing green even when lightly dusted with snow. These species maintain their foliage to take advantage of early spring sunlight before the forest canopy closes overhead.
The final group consists of tropical or non-hardy ferns that possess no natural defense against freezing temperatures. These species, including the popular Boston fern (Nephrolepis exaltata), originate in warmer regions and will suffer tissue damage and death if exposed to frost. Survival in cold climates necessitates bringing these ferns indoors well before the first expected freeze.
Biological Strategies for Winter Survival
Hardy ferns employ several distinct biological mechanisms that allow them to endure sub-freezing temperatures without dying. The most common strategy in deciduous ferns is the initiation of dormancy, a state of reduced metabolic activity triggered by decreasing temperatures and shorter daylight hours in the autumn. During this process, the plant sacrifices its above-ground fronds, redirecting nutrients and energy stores into the underground rhizome structure.
The rhizome, which is the horizontally creeping underground stem, acts as the fern’s protective survival unit. It is typically buried deep enough to avoid the most extreme temperature fluctuations and contains the meristematic tissue—the growing points—protected by dense, insulating scales. This underground location shields the vital parts of the plant from freeze-thaw cycles that can cause cellular damage. The rhizome stores carbohydrates, allowing the plant to rapidly produce new shoots, known as fiddleheads, once spring arrives.
In evergreen varieties, the strategy involves a physiological hardening process to prevent ice crystal formation within the cells. This involves osmotic adjustment, where the concentration of dissolved substances, such as sugars and certain proteins, increases within the plant cells. This higher solute concentration effectively lowers the freezing point of the cellular water, acting as a form of natural antifreeze. Some ferns also produce specialized antifreeze proteins that bind to forming ice crystals in the extracellular spaces, inhibiting their growth and preventing them from piercing cell membranes.
Practical Winter Care and Protection
For hardy ferns planted outdoors, minimizing disturbance and providing a light layer of insulation supports their natural survival mechanisms. It is beneficial to leave the spent, brown fronds on the plant throughout the winter, as this dead foliage acts as a natural protective layer over the crown and rhizomes. After the first hard freeze, applying a protective layer of organic mulch, such as shredded leaves or straw, over the root zone helps stabilize soil temperatures.
Outdoor ferns require minimal to no watering during the winter months, as the plant is dormant and excess moisture can lead to root rot in cold soil. Protection from strong winter winds is important, as they can cause desiccation in evergreen fronds, sometimes warranting a temporary windbreak. Gardeners should wait until early spring, just before new growth emerges, to remove old, damaged fronds and the winter mulch.
Tropical ferns must be prepared for indoor overwintering since they are not hardy in cold climates. Before moving them inside, inspect the fronds and spray them with water to remove any hitchhiking pests. Once indoors, place these ferns in a cool location, ideally with temperatures between 60°F and 72°F, and away from drying heat sources. Since growth slows inside, both watering and fertilization should be significantly reduced until the following spring. Maintaining adequate humidity, often with the help of a pebble tray or humidifier, is key to keeping tropical ferns healthy through the dry winter air.