Fertiliser for Ferns: How to Feed Indoor & Outdoor Ferns for Healthy, Lush Green Growth

Ferns bring tropical elegance to both indoor spaces and shaded gardens. With their graceful fronds and love of moisture, ferns thrive when planted in the right environment—and fed with the right fertiliser. This guide covers fern care for popular varieties like maidenhair, tree ferns, bird’s nest and more, with tips on how to fertilise ferns in pots, gardens, and hanging baskets.

Understanding Fern Growth: What Ferns Need to Thrive

Ferns are ancient, non-flowering plants that reproduce via spores and grow well in low-light, high-humidity environments. Unlike flowering plants, they don’t produce fruit or seeds—so fertiliser should focus on **foliar growth**, **root health**, and **resilience**.

Ideal Growing Conditions:

Light: Indirect light or deep shade. Tree ferns tolerate filtered morning sun. Direct sun will burn delicate fronds.
Soil: Moist, rich, well-drained soil with organic matter. Slightly acidic to neutral pH (5.5–7.0).
Water: Keep soil consistently moist but not soggy. Most ferns prefer high humidity and dislike drying out.
Container Tips: Use a breathable pot (plastic or glazed terracotta) with good drainage holes and fern-friendly potting mix containing coco coir, bark fines, or perlite.

Popular Ferns in Australia:

Maidenhair Fern (Adiantum): Delicate foliage; needs regular misting and feeding.
Bird’s Nest Fern (Asplenium): Thrives indoors; benefits from gentle fertiliser.
Tree Fern (Dicksonia or Cyathea): Prefers cool, shaded gardens with consistent moisture and regular top-feeding.
Boston & Elkhorn Ferns: Hardy and tolerant of pot life or mounted displays, but still need nutrient support.

What is the Best Fertiliser for Ferns?

Ferns are foliage-focused plants that need a balanced fertiliser with **moderate nitrogen**, **low phosphorus**, and **added micronutrients** like iron and magnesium to maintain deep green leaves and avoid yellowing.

What to Look For in a Fern Fertiliser:

Low phosphorus: Ferns are sensitive to overfeeding—avoid high P blends made for flowers or fruiting plants.
Moderate nitrogen: Encourages lush frond growth without overstimulating.
Micronutrients: Iron, magnesium and calcium prevent leaf yellowing and necrosis, especially in maidenhair and indoor species.

Complete Grow Recommendations:

NPK 20-20-20 Liquid Fertiliser – Best for general-purpose fern feeding. Suitable for all indoor/outdoor ferns. Apply monthly during active growth.
Cal-Mag Hydroponic Nutrients Fertiliser – Ideal for maidenhair and tree ferns showing signs of yellowing or leaf curl. Provides essential calcium and magnesium.

How Often Should You Fertilise Ferns?

Indoor ferns: Feed every 3–4 weeks from spring to autumn. Use half strength in winter or pause feeding if dormant.
Outdoor/tree ferns: Apply monthly from the top crown or base. Water in well after feeding.
Maidenhair ferns: Light feeding every 2–3 weeks at half strength. Sensitive to overfeeding—flush soil monthly.

Avoid granular fertilisers unless very slow-release. Liquid or water-soluble formulas are safer and more effective for delicate root systems.

Fern Care FAQs: Troubleshooting Yellow Leaves, Poor Growth & Feeding Issues

Why Are My Fern Leaves Turning Yellow?

Common reasons include:

Underfeeding: Ferns deplete nutrients quickly. Replenish with a balanced liquid fertiliser monthly.
Low humidity or dry soil: Especially common in indoor environments. Mist daily and use pebble trays.
Too much direct sunlight: Fronds scorch easily. Move to bright but filtered light.

Do Maidenhair Ferns Need Fertiliser?

Yes—maidenhair ferns are high-maintenance and need regular feeding with a diluted, balanced fertiliser. They’re particularly prone to yellowing from iron or magnesium deficiency.

Can You Fertilise Bird’s Nest Ferns?

Absolutely. Bird’s nest ferns grow well indoors and benefit from monthly feeding with a gentle, balanced fertiliser during the growing season. Avoid overfeeding, which can deform new leaves.

Best Soil for Ferns:

Use a loose, airy, moisture-retentive mix—ideally one designed for ferns or orchids.
Amend with coco peat, fine bark, perlite, or aged compost.
Ensure pots have drainage and never allow the base to sit in standing water.

With the right fertiliser and consistent care, ferns reward gardeners with lush, vibrant green foliage that brings life to shaded corners, patios, bathrooms, or indoor spaces year-round.