The reason the Adiantum raddianum is most suited for growing in a terrarium or within a conservatory is because it thrives in high humidity conditions that are difficult to provide within most rooms in a house.
This delicate species is in need of a consistent supply of moisture, from the atmosphere and it's soil. You'll find these growing near a water feature in some large buildings and thriving due to it being content with the amount of moisture it's getting and shade.
There are a number of these ferns grown from the Adiantum genus, with the A.raddianum being one of the most popular grown indoors. All of these (about 200 or more) named Maidenhair fern, have similar characteristics and share most of the same care needs to grow well.
How they look: The Delta maidenhair fern displays kind of triangular shaped arched fronds (collection of leaves) with many small pinnate leaves that are light green in color. The black wiry stalks are an interesting characteristic of this species. These stalks give the plant it's stiff upright tree appearance - although they do arch over once they've matured.
Delta Maidenhair Nest Fern (common). -- Adiantum Raddianum (botanical/scientific).
Max Growth (approx):
Poisionous for pets:
Maidenhair Fern Care
The ideal temperature to provide is between 65-75ºF (18-24ºC) for this plant. The minimum is 55ºF (13ºC).
A place with indirect sun is best suited for this fern. If you can provide a fairly shaded place with small amounts of filtered sun then your on to a winner. In their natural woodland habitat they would be shaded by trees, but receive some spots of sun.
Your fern is best kept well watered and the soil to remain moist at all times. Your likely to have problems if you allow the soil to dry out.
A peat based potting mix is required which includes organic matter. If you can sit the pot in a larger pot surrounded with peat moss that will also improve the much needed humidity this plant requires.
Feed from April - September with a diluted fertilizer once a month to encourage healthy growth.
Once every two years during spring will suffice.
Improve humidity levels by placing the plant on a humidity tray with pebbles or use a humidifier. As mentioned above placing the pot in a larger pot surrounded with peat moss also works (double potting). You might just need to test the plant out by trying only misting and one other method and see if any faults arise.
When re-potting in spring and when the plant is large enough you can divide sections. When dividing remove a section of rhizome with the plant by cutting "using a sharp knife". If you have a mature plant that has produced spores (brown spots) on the underside of the leaves it's possible to harvest these, but they're difficult to propagate.
Insects: The most common insect problem is with scale which is noticeable when small brown shells are found of the fronds. Mealy bug can also be an issue.
Frond tips brown: Most likely cause here is dry air and lack of humidity. Increase humidity levels and consider other methods that can provide consistent humidity levels.
Pale fronds or scorch marks: Pale fronds and scorch marks usually appear when the plant has been exposed to too much sunlight. Fronds also turn pale when the fern is lacking fertilizer.
Fronds dying quick: This is usually caused by lack of water. Water the plant thoroughly and mist the leaves frequently in case dry air is also a problem.