Adiantum raddianum aka Delta Maidenhair

Adiantum raddianum is also called Delta maidenhair fern. It belongs to the fern family Pteridaceae. It comes from Mexico, tropical America, and the West Indies. It grows in wet tropical climates and lives for many years. RHS calls it evergreen, meaning it keeps its leaves. NC State lists it as deciduous, meaning it sheds them. This tender fern suits pots indoors, greenhouses, and glass rooms called conservatories.

Plants grow in clumps with fine, arching leaves called fronds. They have creeping stems called rhizomes. Garden height and width reach about 1–2 feet [0.3–0.6 metres]. RHS gives a smaller upper size of 1.6 feet [0.5 metres]. Its own text puts the height near 2 feet [0.6 metres]. Plants grow at a medium rate. They reach their full size within two to five years. The thin fronds form a triangle and split into many parts. Small leaflets are round or shaped like triangles, with lobed edges. New leaves start pale green and darken with age. The wiry leaf stalks shine black, sometimes with a purple tint. Groups of spores lie beneath the leaflets’ folded edges. The fern makes no flowers or fruit. It makes new plants through spores.

Give it bright light indoors, but keep it out of direct sun. Outside, give it part shade. Deep shade can weaken growth, and direct sun can scorch fronds. Keep roots moist in soil that drains well. Dry soil can make fronds die back fast. RHS lists loam with a neutral or alkaline pH. For pots, it suggests peat-free houseplant compost and good air flow. Moist air helps, so a bright bathroom can suit this fern. A tray of damp pebbles can raise moisture in the air around the pot. Give plenty of water as it grows, but less in winter. Feed once a month at half strength from mid-spring through late summer.

Missouri Botanical Garden places it in USDA zones 10–11. NC State includes zone 9b in its range too. RHS rates it H1C, allowing outdoor use during UK summers. Its fine leaves suit hanging baskets and other pots. They also suit glass growing cases called terrariums. NC State suggests sheltered rock gardens with damp pebbles and soil. Deer seldom damage this fern.

Care takes attention, but most pruning means cutting off dead fronds. Scale insects and mealybugs may attack it. Florida fern caterpillars may attack it too. RHS reports few disease problems. Divide the rhizomes in early spring to make more plants. You can also grow plants from spores. They need warmth of at least 21°C.