An important factor in determining the suitability of a plant to your home and envisioning the care it will need, is to know the origin of the plant. Plants that are native to desert regions will require substantial amount of sunlight and loose, fast-draining soil. Plants from the floor of a rainforest will need some protection from strong sunlight and generous humidity.
Maidenhair ferns are not named for their soft, gentle foliage, but for the shiny, black stems common to most Adiantum. Some temperate maidenhair ferns can be grown outdoors in our area but those popular and successful as houseplants are from tropical and sub-tropical origins, where they grow on the high-nutrient, spongy, forest floor. Maidenhair ferns grow on rhizomes that give them greater resilience in dry conditions. They are not the easiest ferns to grow but their delicate beauty is worth some extra effort.
Maidenhair ferns are forest dwellers in origin and need protection from strong sunlight. Indoors, provide indirect, bright light rather than the shade they prefer outside. A north window or at a short distance from an eastern or western window is usually successful.
Water moderately, making the soil damp but not wet, and checking back after 15 minutes to remove any water sitting in the plant's run-off dish. When the plant is in active growth, allow the soil to dry at a depth of one inch between waterings.
The most common cause of failure for maidenhair ferns is low humidity. These delicate ferns prefer greater that 60% humidity which can be difficult to provide in the home. Extra watering will not compensate for a lack of humidity. The easiest way is to grow the plant in a large terrarium or under a glass dome/ cloche. You can also help increase the humidity by growing the plant on a wet pebble tray. A humidity meter (hygrometer) will help you determine whether your environment is offering the plant what it needs.
Typical home temperatures, in the 60 to 70°F. range, are fine. Do not let the temperature fall below 50°F.
Re-pot in early spring only after roots appear out of the top of the soil, approximately every two years. Retention of moisture, slight acidity, as well as good drainage are essential, so use a soil-based mixture with added peat and sharp sand. If your plant has been potted in a peat mixture, additional feeding is required. Do not bury the rhizomes when you re-pot.
Feed every two to four weeks, with a standard houseplant fertilizer, from March through September. If the fern is planted in a mixture of soil and peat, once a month is adequate. A peat-based potting mixture increases the feeding frequency required to every two weeks.
Problems commonly arise when the fern's roots have been exposed to extremes of moisture -- dryness followed by wetness. Keep a more even level of slight dampness for a healthy plant.
Fronds will die after six months or so and should be cut away. Occasionally, the plant has a rest period during which all the leaves die-back and new growth appears after several weeks.