University of Vermont Extension 
Department of Plant and Soil Science

Fall Article

GROWING FERNS SUCCESSFULLY INDOORS

By Dr. Leonard Perry. Extension Professor

Looking for a houseplant that requires little care, thrives in low-light conditions, and adds visual interest to a room?  The answer is the fern, which has foliage ranging in appearance from delicate to dramatic, depending on plant family.

Ferns do best with indirect lighting.  A north-facing window is ideal although during the winter months, when the sun is low on the horizon, an east window is fine for these plants.  Avoid south and west-facing windows, as the intense sunlight may scald the leaves or fronds of the ferns, depending on the intensity of the light.  Or they may dry out faster or scald the leaves if there is low moisture in the soil or air.

Most ferns like an average room temperature of 65 to 75 degrees F during the day, up to 10 degrees cooler at night.  If temperatures exceed 75 degrees F, you may need to water more frequently.  Below 60 degrees, add water only when the soil is dry to the touch.  Some of the more tropical ferns may grow poorly, preferring the higher temperatures.

Consistent watering, keeping the soil evenly moist, not wet, is also key to the health and well being of the plants.  Overwatering causes the fronds to yellow and wilt and may eventually lead to root rot and fungal diseases, especially if the pot is allowed to sit in water.  Too little water also causes wilt.  A few varieties, such as Rabbit's Foot Fern, Brake ferns, and Holly Fern are an exception to the consistent watering rule.  For these, you may allow the soil to dry out slightly between waterings.

Ferns, many of which are native to the tropics, like high humidity, which is why they do well in bathrooms.  But you also can increase humidity around the ferns by placing the pots on a pebble-lined tray.  Add water to the pebbles, making sure the bottoms of the pots do not touch the water in the tray.  The evaporation will add extra humidity around the plants.  The best solution is to have a room humidifier adjacent to the plants.  This also benefits people indoors in dry homes as well.  Homes  often have five to 10 percent relative humidity.  Humidifiers might raise that to 30 to 50 percent, which is really minimum for ferns to do best (although they may tolerate slightly lower humidity), and in native climates often have 70 percent or higher relative humidity.

Or double pot your ferns to provide more moisture.  Place the main container into a second, larger container that you have lined with moist sphagnum moss.  Keep the moss moist or even wet.  Use plastic pots, which don't dry out as quickly as clay pots.  The latter are not recommended for many ferns indoors, unless you use the pot in pot method as described above.  A clay pot surrounded by moss then the ceramic or plastic pot on the outside is probably ideal.

In addition, misting the foliage, especially in winter, will increase the humidity.  Just be careful not to mist the furniture and outer walls.  Use room temperature water as cold water may spot the leaves. You'll know when the humidity is too low as the tips of the fronds will brown or die back.  Maidenhair, Staghorn, and Boston Fern are especially susceptible to lack of adequate humidity.

Ferns require only light feedings of fertilizer once a month from April through September unless actively growing in winter months.  Apply liquid houseplant fertilizer at about one-half the recommended rate.  Too much fertilizer will scorch the foliage.  Newly potted plants should not be fertilized for four to six months, again unless there are indications of active growth.

Plant diseases are rare in ferns grown indoors although your plants may suffer from infestations of scale insects, mealybugs, and mites.  Handpicking or spraying with water are the best options for control as pesticide sprays may injure ferns.  If you must use, choose the least toxic product for the pest and read the label carefully before applying.  Check at least weekly to catch pests early.  If ferns are infested with scales, the easiest way to control is to cut off affected fronds.  If infestation of out of control, you may need to discard the plant before the rest of your houseplants are affected.

Ferns will require repotting every few years.  Repot in the spring, using a purchased soil-less mix that is 50 percent peat moss.  Divide overcrowded plants by removing from the pot and cutting carefully between rhizomes (fleshy roots).  Keep as many leaves as possible per division.

It is also possible to propagate new plants by spores.  In the summer plants will produce spores (brown dots) on the undersides of the leaves.  When these spores darken, remove the leaf and place in a paper bag.  As the leaf dries out, the spores will fall off.  Plant in a peat-based seed starting mix.  Water well, and place in a plastic bag.  Temperatures of 65 to 70 degrees will encourage sprouting.

When fronds are one-inch high, remove the plastic bag and transplant in groups in small pots.  At two to three inches, transplant to individual pots.  This can be tricky as it often takes quite a while for fronds to reach transplant height, and moss and algae or other growth may appear first and kill off young plants, so be forewarned if you decide to propagate your own ferns.

The following ferns can be grown as houseplants.  Or ask your local garden center for recommendations.

--Birdsnest Fern (Asplenium)--one of the easiest ferns to grow; may reach 18  to 24 inches tall although in humid room like greenhouse might get to be six feet high and across; has broad, light green, leathery, undivided fronds that grow upwards, giving the plant the look of a bird's nest.

--Boston Fern (Nephrolepis)--also known as the ladder or sword fern; has long, delicate fronds and light green foliage; grows from 10 inches to three feet, depending on cultivar; ideal for hanging baskets; fern may drop leaflets, especially if too dry, making this a "messy" plant to grow; some newer dwarf compact cultivars are an excellent choice for a houseplant. These were especially popular in Victorian times.

--Brake Ferns (Pteris)--several varieties are available, including some with variegated foliage; may be grown as a table fern or in a hanging basket; prefers diffused light and nighttime temperatures of 50 to 55 degrees F, 68 to 72 degrees F during the day.

--Button Fern (Pellaea)--good plant for small spaces as it only grows 12 to 18 inches tall; it is often dark green and has round, slightly leathery "button-like" leaves attached to slender stems.

--Holly Fern (Cyrtomium)--also known as the fishtail fern; has bright, glossy, leathery leaves; rather un-fernlike in appearance; prefers cool to moderate temperatures and indirect sunlight; requires less humidity than most other ferns; ideal for lower light conditions.

--Maidenhair Fern (Adiantum)--fast-growing fern that needs high humidity and consistent moisture to survive; foliage is lacy with small, fan-shaped leaves; does best in a north window. If it dries out, the foliage may die as the plant shrivels.  However, it  doesn't "unwilt" when watered as many houseplants will, but new shoots should appear.

--Rabbit's Foot or Ball Fern (Davallia)--excellent fern for hanging baskets as the furry, creeping rhizomes hang over the edge of the container, resembling a rabbit's foot; needs to be planted with rhizome above soil level instead of buried; very sensitive to salt and thus needs to be watered with soft water.

--Staghorn Fern (Platycerium)--leaves are wide, flat, down-covered, and resemble an elk's antlers; slow-growing but can reach three to four feet in height; should be grown in sphagnum moss with the shield (the brown part from which the green "antlers" emerge) wired to a piece of wood or cork bark; fern is really marginal in many interiors as it needs lots of humidity; water by taking entire wood slab or cork bark and moss off the wall or wherever it is hanging, then immerse with plant shield into a pan or tub of water.  A bath tub without soap suds works best.  Water should be lukewarm, not hot.  Allow to drain before rehanging.


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