Winterizing ferns prepares them to withstand harsh winter conditions like freezing temperatures, drying winds, and limited daylight. This protective process helps ensure they remain healthy for the next growing season, whether they reside outdoors or indoors.
Understanding Fern Hardiness
Fern hardiness, their ability to tolerate cold, is linked to USDA Plant Hardiness Zones, which categorize regions by average annual extreme minimum winter temperature. Hardy ferns, typically perennials, survive outdoors in zones 3 to 8, such as Christmas ferns (Zone 3) and Japanese painted ferns (Zone 5).
Tender ferns, like tropical Boston ferns, cannot withstand freezing temperatures and need indoor protection; even a light frost can damage their fronds and root systems. Knowing your fern’s hardiness and local USDA zone is crucial for winterizing.
Winterizing Outdoor Ferns
Preparing outdoor ferns for winter involves several practical steps to ensure their survival.
Preparing the Site
In late fall, clean up dead fronds, leaves, and debris from around the fern’s base. Do not cut back all green foliage unless diseased or heavily damaged, as these fronds provide natural insulation to the plant’s crown and roots. Decaying fronds also contribute organic matter to the soil as they break down.
Mulching for Protection
Apply a thick layer of organic mulch around the base of outdoor ferns to insulate their root systems from extreme cold and prevent frost heave, which occurs when freezing and thawing cycles push shallow-rooted plants out of the soil. Straw, shredded leaves, or pine needles work well. A two to four-inch layer, applied after the first hard freeze, provides sufficient protection.
Additional Winter Shields
In very cold or windy climates, additional protection is beneficial. Temporary wind barriers, like a fence or mesh, shield ferns from drying winter winds. For individual plants, creating a mini-cloche with stakes and horticultural fabric or wrapping them in burlap offers extra insulation against severe cold and heavy snowfall. Ensure any covering allows adequate air circulation to prevent moisture buildup.
Winterizing Indoor Ferns
Bringing tender ferns indoors for winter requires careful attention to their transition and ongoing environmental needs.
Transitioning Indoors
Move tender ferns indoors before the first frost, ideally when outdoor nighttime temperatures approach 45-50°F. Before bringing plants inside, inspect them thoroughly for pests. Hosing down the entire plant, including frond undersides, removes dirt, dust, and many insects. For a more thorough cleanse, submerge the potted plant in water for several hours to drown or uncover hidden pests.
Adjusting Environmental Conditions
Once indoors, ferns need specific conditions. Maintain adequate humidity, as indoor heating systems dry the air. Achieve this through regular misting, placing pots on pebble trays filled with water (ensuring the pot does not sit in water), using a room humidifier, or grouping plants. Ferns prefer bright, indirect light; place them near a north or east-facing window, avoiding direct sunlight that can scorch fronds. Reduce watering frequency as growth slows; allow the topsoil to dry slightly between waterings to prevent root rot.
Monitoring for Pests
Indoor environments are conducive to common houseplant pests like spider mites, mealybugs, and aphids, which thrive in dry conditions. Regular inspection of leaves, stems, and pots catches infestations early. If pests are found, initial treatments include physically wiping them off or spraying with water. For persistent issues, apply insecticidal soap or neem oil, ensuring the product is safe for ferns.
Spring Transition and Revival
As spring approaches, gradually transition ferns back to active growing conditions. For outdoor ferns, remove protective coverings like burlap or cloches once the danger of hard frost has passed. Thin or refresh any heavy mulch as temperatures rise. For indoor ferns, wait until all frost risk has passed before slowly reintroducing them outdoors, gradually acclimating them to brighter light and changing temperatures over days or weeks.