Delta maidenhair fern

Sun

Bright, indirect light indoors; sheltered partial to full shade outdoors. Avoid strong midday and afternoon sun.

Water

Keep the root ball consistently moist but not waterlogged. Water thoroughly when the surface just begins to lose moisture, and empty standing water from saucers.

Soil

Humus-rich, moisture-retentive soil with good drainage; use an airy, peat-free houseplant compost in containers.

Height

1-2 ft (0.3-0.6 m)

Spread

1-2 ft (0.3-0.6 m)

Foliage

Evergreen. Arching, triangular fronds with small, bright green, fan-shaped leaflets on slender, glossy black stalks. Spores form beneath folded leaflet margins.

Growth

Moderate in warm, moist conditions

Care needed

High

• Deer resistant
• Heat tolerant
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Hard

Toughness

Needs looking after

Pick your zone, country, light and whether you have pets.

1. Planting day

   1 ft (0.3 m)

2. After 1 year

   1.1 ft (0.35 m)

3. After 2 years

   1.3 ft (0.4 m)

4. After 3 years

   1.5 ft (0.45 m)

   full size

About 3 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Mildly toxic: may upset a stomach

Invasive in

the US

Growth rate

Moderate

• Check container moisture frequently; even a brief drying-out can turn the fronds brown.
• Provide humid air and keep away from heating vents, air conditioners and drying winds.
• Feed monthly at half the labelled strength during active spring and summer growth.
• Keep containers freely draining; never leave the pot standing in water.
• Repot in spring when roots fill the pot, moving up only one pot size.
• Bring outdoor pots inside before nights fall below 50°F (10°C).

Pruning. Cut brown or damaged fronds back to their bases whenever needed, using clean scissors. If the foliage dries out completely, remove dead fronds and maintain gentle moisture; a living rhizome may produce new growth.

Early spring

Remove dead fronds and check whether crowded plants need repotting or division.

Spring

Begin dilute monthly feeding as fresh fronds develop.

Late spring

Move pots outdoors only after nights stay above 50°F (10°C), acclimating them in deep, sheltered shade.

Summer

Check moisture daily during hot weather and protect plants from sun and drying wind.

Autumn

Bring summer outdoor plants indoors before cool nights; inspect them for pests first.

Winter

Keep in bright, indirect light away from heaters; reduce watering frequency if growth slows, but never let the root ball dry out.

• Use in shaded courtyard containers where its fine foliage softens hard paving and walls.
• Plant beneath broad-leaved tropical plants for a contrast in leaf size and texture.
• Display in a bright, humid bathroom away from direct sun and cold draughts.
• Group with other moisture-loving houseplants to create a layered indoor planting.
• Use beside shaded paths in frost-free gardens where its delicate fronds can be seen close up.

Garden styles it suits: Woodland, Tropical, Modern courtyard, Victorian, Green on green and Small-space.

Plant it with: Bird's nest fern, Cast iron plant, Peace lily, Parlour palm and Rex begonia.

Wildlife: Provides small-scale shelter for invertebrates in suitable outdoor gardens. It produces neither flowers nor nectar.

• Crisp, brown fronds usually follow dry compost, dry air or hot sun. Restore even moisture, increase humidity and move into gentler light.
• Yellowing fronds and collapsing growth can indicate waterlogged roots. Empty saucers, check drainage and repot if the compost remains saturated.
• Spider mites cause pale stippling and fine webbing in dry conditions. Isolate the plant, rinse foliage gently and use a product labelled for mites and suitable for ferns if needed.
• Scale insects and mealybugs collect on stems and leaflet undersides. Isolate the plant, remove visible pests and repeat treatment with a product labelled as safe for ferns.

Not known to be toxic to cats, dogs, horses or people. No part is recognised as poisonous, though eating foliage may cause mild stomach upset and it is not a food plant.

Where it spreads. Can escape into damp, shaded habitats. It is regarded as invasive in Hawaii and parts of New Zealand, and is naturalised in parts of eastern Australia. Check local guidance before planting outdoors in these regions.

• Southern maidenhair fern (Adiantum capillus-veneris)

  Its fertile leaflet edges usually carry elongated spore-bearing flaps rather than the more rounded flaps of delta maidenhair. The foliage is otherwise very similar.

• Northern maidenhair fern (Adiantum pedatum)

  Its fronds branch into a distinctive horseshoe-shaped or hand-like arrangement, unlike the roughly triangular fronds of delta maidenhair.

• Large-leaf maidenhair fern (Adiantum macrophyllum)

  Has much larger, elongated leaflets, often pink or reddish when young, rather than numerous small green fans.

Adiantum comes from Greek for 'unwetted', referring to the water-shedding foliage, while raddianum honours the Italian botanist Giuseppe Raddi.

Propagation. Divide an established clump in spring, keeping roots, rhizome and several healthy fronds on each section. Spores can also be sown on a clean, moist growing medium under humid conditions, but development is slow and requires careful hygiene.

Accepted botanical name

Adiantum raddianum

In the US and Canada

Introduced in Hawaii.

Native range

Argentina Northeast, Argentina Northwest, Bolivia, Brazil Northeast, Brazil South, Brazil Southeast, Brazil West-Central, Colombia, Costa Rica, Ecuador, Guatemala and Haiti.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.