The Boston fern, or Nephrolepis exaltata, is a popular houseplant admired for its lush, arching fronds and vibrant green foliage. While commonly grown indoors, the plant is native to tropical and subtropical regions, which creates some confusion about its placement. The Boston fern is technically an outdoor plant, but only in specific, warm climates. It thrives best outdoors under certain seasonal conditions in most other areas. Its requirement for consistent warmth and high humidity means it is generally cultivated as an indoor specimen that can be temporarily moved outside.
Understanding the Boston Fern’s Natural Habitat
The Boston fern is indigenous to the humid, shaded environments of swamps and forests in Florida, Mexico, Central America, the West Indies, and Africa. These native areas provide the consistent warmth and moisture the fern requires to flourish.
The plant’s tropical heritage dictates its intolerance for cold temperatures. The Boston fern prefers a daytime temperature range between 60°F and 75°F, with slightly cooler nights around 55°F to 65°F. Exposure to temperatures below 50°F can cause the delicate fronds to die back and result in stunted growth. Temperatures at or near freezing, below 35°F, are detrimental and will kill the plant entirely. For this reason, the fern can only be considered a permanent outdoor plant in USDA Hardiness Zones 9 to 11, where frost is rare or non-existent.
Growing Boston Ferns Outdoors Seasonally
For gardeners living outside of the frost-free zones, the Boston fern can still be utilized as an outdoor accent during the warm season. The proper timing for moving the plant outdoors is after all danger of frost has passed in the spring, typically when nighttime temperatures consistently remain above 50°F. Moving the fern outside too quickly can cause leaf shock or burn, so a process of acclimatization, known as hardening off, is recommended.
Acclimatization involves gradually introducing the plant to the outdoor environment over a week or two. Start by placing the fern in a sheltered, shady spot for a few hours each day, slowly increasing the duration of its outdoor stay. This process prepares the plant for the slightly brighter light and increased air movement it will encounter outside. The fern should be situated in a location that receives bright, indirect light, such as a covered porch or under a dense tree canopy, to prevent scorching in direct sun.
The fern must be brought back indoors before the weather turns cold in the autumn. A good indicator is when overnight temperatures begin to dip consistently below 55°F. Bringing the plant inside at this time ensures it avoids the damaging effects of cold stress and frost, allowing it to be overwintered successfully until the next spring.
Adjusting Care Routines for Outdoor Placement
Once a Boston fern is moved outdoors, its daily care requirements change significantly compared to being inside. The increased heat, sun exposure, and air circulation found outside cause the potting mix to dry out much faster. Outdoor ferns, especially those in containers, often require much more frequent watering, potentially needing water daily or even twice a day during hot summer periods to keep the soil consistently moist.
Fertilization schedules may also need adjustment during the active growing season outside. While ferns are light feeders, they can benefit from a diluted, balanced liquid fertilizer applied every four to six weeks. Alternatively, gardeners can incorporate a slow-release fertilizer or an inch of compost into the soil mix in the spring.
The outdoor environment also introduces the fern to pests not typically found indoors. Gardeners should monitor for common outdoor pests like slugs, which are attracted to the moist foliage and can cause damage to the fronds. Other potential pests include:
- Scale
- Mealybugs
- Spider mites
These pests can be managed by regularly inspecting the plant and treating infestations with horticultural oil or a strong spray of water.