Winterizing ferns is a preparatory process designed to help these foliage plants survive the cold, dormant months and ensure robust growth the following spring. This preparation involves adjusting the fern’s environment and care routine to protect its root structure, which stores energy during the winter. Since ferns originate from diverse native climates, the specific method of winterization depends entirely on the species. Proper preparation is necessary because freezing temperatures can destroy the plant’s crown and rhizomes, preventing the emergence of new fiddleheads.
Understanding Fern Types for Winter Care
Fern species are categorized into two groups based on their hardiness to cold temperatures, which dictates the winter care they require. Hardy ferns are native to temperate regions and naturally withstand freezing ground temperatures. Species like the Ostrich Fern (Matteuccia struthiopteris) and the Japanese Painted Fern (Athyrium niponicum) are examples of this category. These ferns typically enter a period of dormancy outdoors and do not require relocation.
Tender or tropical ferns, conversely, originate from warm climates where frost is nonexistent. The popular Boston Fern (Nephrolepis exaltata) and the delicate Maidenhair Fern (Adiantum spp.) fall into this group. Because their cellular structure cannot tolerate freezing, they must be protected from frost. Winter survival necessitates moving them indoors to a climate-controlled environment before the first sustained drop in temperature.
Preparing Hardy Ferns for Outdoor Wintering
Preparation for hardy ferns that remain in the ground begins after the first light frost, but well before the soil is expected to undergo a hard freeze. For deciduous species, the foliage will often naturally collapse, providing a layer of self-protection. Gardeners can cut back the dead fronds in late fall or wait until early spring to remove the old growth. Leaving the dead fronds in place provides additional insulation for the central crown of the plant.
The most effective step for outdoor wintering is applying a protective mulch layer over the fern’s root zone and crown. This insulating blanket stabilizes the soil temperature and prevents the damaging freeze-thaw cycle known as “heaving,” which can push shallow-rooted plants out of the ground. A thick layer of organic material, such as shredded leaves, straw, or pine needles, should be spread approximately 4 to 6 inches deep around the base of the plant. Ensure the mulch material does not become compacted, which inhibits air circulation and potentially leads to rot.
Before the ground freezes solid, the area around the ferns should be thoroughly watered, ensuring the soil is moist but never saturated. Adequate moisture helps protect the roots from desiccation during the cold, dry winter air. Once the soil is frozen, the roots cannot absorb water, making this late-season watering a preventative measure against winter burn.
Moving and Caring for Tender Potted Ferns
Potted tropical ferns must be transitioned indoors when nighttime temperatures consistently drop below 50°F, ideally before the first frost occurs. Before moving the fern, a thorough inspection for pests is necessary to prevent infestations of other houseplants. Common pests include spider mites, mealybugs, and scale insects, which often reside on the undersides of the fronds. Treating the fern with insecticidal soap or neem oil is recommended, ensuring all leaf surfaces are saturated, followed by a few days outdoors to allow the treatment to work before moving the plant inside.
Once indoors, the fern should be placed in an area that receives bright, indirect light, such as near an east-facing window. Avoid the intense heat of south or west-facing windows, which can scorch the delicate foliage. The change from humid outdoor air to dry indoor heat is the greatest challenge for tropical ferns. A humidity level between 40 and 50 percent is preferred to prevent the frond tips from browning and drying.
To increase the local humidity, the pot can be placed on a shallow tray filled with gravel and water, ensuring the bottom of the container remains above the waterline. Double-potting, where the fern’s container is nested inside a larger pot with moist sphagnum moss packed in the gap, is also effective. Watering frequency must be significantly reduced during the indoor winter period, as the fern’s growth slows considerably. The soil should be allowed to dry slightly to the touch between waterings, preventing the soggy conditions that lead to root rot.