Caring for Your Outdoor Boston Ferns During the Cold Winter Months

With their graceful, cascading fronds, Boston ferns add beautiful greenery and texture to outdoor spaces. However, keeping these tropical plants alive through freezing winter temperatures can be a challenge. By understanding Boston fern care and implementing some protective strategies, you can increase the odds of your ferns surviving the winter.

An Overview of Boston Ferns

Boston ferns (Nephrolepis exaltata) are one of the most popular ferns grown as houseplants and in outdoor plantings. Growing up to 5 feet long, the arched green fronds create a graceful, flowing appearance.

Native to tropical regions, Boston ferns thrive in warm, humid conditions with mild winters. When temperatures drop below freezing, they can suffer severe damage. If you live in USDA plant hardiness zones 8 or above, you may be able to leave Boston ferns outside year-round if properly protected. Any colder, and they will need to be overwintered indoors.

Preparing Boston Ferns for Winter Outdoors

If you want to keep your Boston ferns in the garden over winter, take these steps to prep them:

• Trim off any dead or damaged fronds in early fall so the plant can focus its energy on the healthy foliage

• Provide a slow-release fertilizer in early fall to nourish the plant before dormancy.

• Water deeply before the first frost Hydrated plants better withstand cold damage

• Add a 4-6 inch layer of mulch around the base to insulate roots. Leaves or pine straw work well.

• Place outdoor ferns near the house foundation or under trees for shelter.

• Consider portable heaters on frosty nights if ferns are in exposed areas.

• Cover ferns with frost cloth if extreme cold is forecasted. Secure it well.

• Avoid pruning late in fall so fronds can remain to help insulate the crown.

Ideal Winter Conditions for Outdoor Boston Ferns

Even in warm climates, Boston ferns grown outside need protection from winter extremes:

• Temperatures: Ideal temps are 60-80°F. They tolerate brief light frosts to the low 30s°F if protected.

• Light: Bright, indirect light is best. Reduce water slightly in brighter light.

• Water: Water 1-2 times monthly if rainfall is scarce, enough to moisten the soil.

• Humidity: Mist ferns frequently on sunny winter days. Humidity trays help too.

Monitor weather forecasts daily and adjust care as needed to maintain the preferred conditions.

Dangers to Avoid with Outdoor Winter Fern Care

While Boston ferns are resilient, there are a few hazards to avoid:

• Freezing temperatures – Even a brief hard freeze can blacken and kill fronds. Cover plants at the first sign of frost.

• Cold winds – Desiccating winter winds zap moisture from fronds. Use sheltered spots or windbreaks.

• Overwatering – Too much winter water leads to root rot. Allow soil to partially dry between waterings.

• Dry air – Low winter humidity dries fronds. Mist often and use humidity trays.

• Sun scalding – Harsh winter sun can burn fronds. Filter light with shade cloth if needed.

• Heavy snow or ice – Weigh down and crush fronds. Carefully shake off snow before it compacts.

With attentive care, you can help your outdoor Boston ferns survive and even thrive through the winter months.

Providing Winter Water for Outdoor Boston Ferns

Caring for outdoor Boston ferns in winter revolves heavily around proper watering. While they need moisture to survive, overwatering during cold weather quickly causes problems.

Here are some tips for winter watering:

• Water less frequently, only when the top couple inches of soil become dry. This may be every 2-4 weeks depending on rain.

• When watering, drench the soil thoroughly until water drains from the bottom of the pot. This encourages deeper root growth.

• Always pour off any water collecting in saucers beneath pots after watering so ferns don’t sit in excess moisture.

• Mist fronds every few days with a spray bottle on sunny days to compensate for low humidity.

• If possible, use collected rainwater or melted snow which contains no salts or chemicals.

• In dry climates, sinking pots into the ground helps retain moisture longer. Mulch well around partially buried pots.

Adjust your watering habits to match winter’s cooler, slower growth. Maintain moist but not constantly wet soil.

Protecting Boston Ferns from the Elements

Outdoor ferns need protection from harsh winter conditions. Here are some effective options:

• Cold frames – Mini greenhouse-like structures maintain warmer temperatures and humidity while allowing air flow.

• Cloches – Bell jars or cloches trap warmth around plants. Ventilate on sunny days.

• Frost cloth – Breathable fabric drapes provide 4-8 degrees of cold protection if secured snugly.

• Burlap – Wrap burlap around ferns and stakes to insulate from wind and frost.

• Mulch – A thick layer of shredded leaves or pine straw keeps roots warmer and moist.

• Tree canopy – Situate ferns under trees where the canopy provides shelter.

• South side of home – The radiant heat from brick or stucco walls provides subtle warming.

Choose options that fit your climate and ferns’ exposure. A combination of methods may be needed for maximum protection.

Overwintering Boston Ferns Indoors

In climates colder than USDA zone 8, overwintering Boston ferns indoors is advised. Ideally bring them inside a few weeks before your average first frost date.

Follow these tips for overwintering indoor Boston ferns:

• Prune back long fronds by a few inches before bringing inside to fit the space.

• Select a bright room with southern or eastern exposure for winter sunlight.

• Water slightly less, allowing the soil to dry some between waterings.

• Mist fronds daily to boost humidity around the plant.

• Keep indoor winter temps between 60-70°F. Avoid drafts.

• If fronds yellow, move to a shadier spot away from direct light.

• Return outside after the last frost when nighttime temps are above 50°F.

• Transition ferns slowly back into direct sun over a week or two. Watch for sun scalding.

With the right winter accommodations, Boston ferns can survive outdoors even in cooler climates, emerging revitalized when spring arrives. Pay close attention to their needs, and you can enjoy their graceful beauty all year long.