Ferns are popular in gardens and indoor spaces for their lush foliage. Gardeners often wonder if frost can kill ferns and what factors influence their survival in cooler temperatures. This article clarifies the impact of frost on different fern types and provides care guidance.
Fern Types and Frost Tolerance
Ferns vary significantly in their ability to withstand cold temperatures, largely due to their natural habitats and evolutionary adaptations. This distinction helps predict how a fern will react to freezing conditions.
Hardy ferns, native to temperate regions, possess mechanisms to survive cold winters. Examples include the Ostrich fern (Matteuccia struthiopteris), Christmas fern (Polystichum acrostichoides), and Lady fern (Athyrium filix-femina). Many are deciduous, with fronds dying back in fall as the plant enters dormancy, protecting its crown and rhizomes underground.
Other hardy ferns, such as the Christmas fern, are evergreen with foliage that tolerates freezing. Their cell structures prevent significant ice crystal formation, allowing them to endure cold snaps and resume growth. These adaptations allow hardy ferns to survive frost and thrive again with warmer weather.
In contrast, tender or tropical ferns from warmer climates lack natural cold tolerance. Varieties like Boston, Maidenhair, and Staghorn ferns are highly susceptible to frost damage. Their cellular structures are not equipped to handle freezing, and frost exposure often leads to severe damage or death.
The Impact of Frost on Ferns
Frost damages fern tissue by forming ice crystals within plant cells. As temperatures drop below freezing, water inside cells freezes, expands, and ruptures cell walls. This internal damage compromises the cell’s integrity and function.
Freezing temperatures also draw water out of plant cells, leading to dehydration. Visible frost damage includes fronds that appear blackened, mushy, or shriveled, a direct result of destroyed cellular structure and turgor loss.
Damage can range from superficial, affecting only the outermost foliage, to lethal, where the crown or rhizomes are destroyed. If only the fronds are damaged, the fern may recover from its root system. However, if the plant’s growing point is compromised, recovery becomes unlikely.
Protecting Your Ferns from Frost
Protecting ferns from frost is important, especially for tender varieties or when harsh conditions are expected for hardy types. Potted tender ferns should be brought indoors before the first frost. Placing them in a bright, humid location helps them transition and thrive through colder months.
For outdoor hardy ferns, particularly newly planted specimens, applying organic mulch around the crown provides insulation. Materials like straw, fallen leaves, or wood chips, spread several inches deep, help regulate soil temperature and protect rhizomes from extreme cold.
During unexpected cold snaps, covering outdoor ferns with a frost cloth, burlap, or even an old blanket can offer temporary protection. These covers trap ground heat, creating a warmer microclimate around the plant. Proper watering before a freeze can also be beneficial, as moist soil retains heat more effectively than dry soil, providing a buffer against temperature drops.
Post-Frost Care and Recovery
After a frost event, assess the damage to your ferns and provide appropriate care. For hardy ferns, wait until spring to determine the full extent of the damage and if new growth emerges. It can be difficult to differentiate between dormancy and severe damage immediately after a freeze.
Once new growth begins in spring, prune any fronds that are clearly damaged—blackened, shriveled, or mushy. This removes dead tissue and allows the plant to direct energy towards new, healthy growth. Avoid pruning too early in winter, as the damaged fronds can offer some protection to the crown from subsequent cold.
For tender ferns showing signs of potential recovery, such as green near the base, light watering is recommended. Avoid heavy fertilization until vigorous new growth is evident, as the plant needs to recover its root system first. Hardy ferns typically recover vigorously from frost damage, producing a flush of new fronds. While some tender ferns might show signs of life after light frost, many will not fully recover.