Humidity Requirements for Bird's Nest Fern

The bird's nest fern's solid fronds don't need as much humidity.

The bird's nest fern's solid fronds don't need as much humidity.

A bird’s nest fern's (Asplenium nidus) unusual uncut fronds give a clue as to why this rainforest understory dweller is one of the easiest ferns to grow indoors. Its epiphytic nature provides another. As with other ferns, the bird’s nest fern needs higher humidity to stay healthy and grow well.

Asplenium Facts

The bird's nest fern is just one of the understory ferns that grow in the still, moist warmth of the tropical rainforest where daytime temperatures seldom rise above 70 degrees Fahrenheit and nighttime temperatures seldom fall below 60 F. Temperatures beyond the canopy may rise above 90 F during the day, but understory temperatures remain within a limited range due to two factors: limited light and stifling humidity. The bird's nest fern’s adaptability to conditions indoors -- or outdoors in U.S. Department of Agriculture plant hardiness zones 10 and 11 -- arises from its epiphytic habit.

Epiphytic Adaptation

The bird’s nest fern is an epiphyte, meaning it derives its nutrients and water from the air around it. This habit allows the bird’s nest fern to colonize the sides of trees in the forest, spreading toward the greater light and lower humidity of the forest canopy or downward from the canopy toward the uniformly warm floor where relative humidity may rise over 70 percent. The fern adapts easily to any rich soil or fibrous slab of wood and catches rainwater and moisture in its cup-shaped base. The fern’s vertical travels through the understory have trained it to adapt to varied levels of light and humidity.

Garden Ferns

Outdoors, bird's nest ferns grow 2 to 4 feet tall in partial to full shade. Outdoor humidity is usually enough, especially on the foggy coast, to keep them healthy and encourage epiphytic growth on nearby trees. They will grow best and biggest in USDA zones 10 and 11. The fern may also grow in USDA zone 9, but should be either sheltered or brought indoors so low winter temperatures or drying winds cannot damage fronds. Planting ferns in a humus-rich soil helps hold moisture and close shade contains evaporating moisture, easily maintaining 50 to 70 percent relative humidity.

Indoor Ferns

Understory plants adapt easily to indoor light levels, but humidity can be a problem because both central heating and air conditioning remove humidity from air. Winter humidity levels are lowest, sometimes dropping below 10 percent. Tough ferns, such as bird’s nest ferns, can survive with humidity levels from 30 to 50 percent,although added humidity from a humidifier, pebble tray or daily misting will help prevent the fronds from turning brown on their edges. The low-end relative humidity level for a bird’s nest fern that lives indoors, according to the University of Georgia Extension, is 40 percent.

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