Growli
Let's go

Fertilising guide

How to fertilise Wart Fern (Microsorum scolopendria)— schedule & NPK

Also called Wart Fern, Oak Leaf Fern, Climbing Bird's Nest Fern.

More about wart fern

About Wart Fern

Microsorum scolopendria · also called Wart Fern, Oak Leaf Fern · houseplant

The wart fern is a creeping epiphytic fern from Pacific and tropical-Asian forests, named for the wart-like sori dotting the undersides of its glossy, deeply lobed fronds. It spreads by a long-running surface rhizome rather than a crown, climbing logs and walls. Grown indoors it rewards bright-indirect light, steady warmth, high humidity, and an open, bark-rich mix.

Growth habit: Vigorous creeping epiphyte that advances on a thick, scaly surface rhizome, throwing up individual leathery, pinnately lobed fronds along its length; happily climbs bark, mounts or a moss pole.

What fertiliser wart fern actually wants — and why

Wart Fern is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.

A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula.

For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for wart fern: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.

How often to feed wart fern, and which months

Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For wart fern:

Feed monthly through spring and summer with a balanced liquid fertiliser diluted to half strength. Ferns are salt-sensitive, so flush the mix occasionally and pause feeding in autumn and winter. Treat that as monthly between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.

The dormant-season rule matters more than the exact interval: skip feeding entirely when wart fern is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.

What strength to mix for wart fern

Half strength is the safe default for wart fern — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.

Feeding always goes onto already-damp soil, never dry roots — water wart fern first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the wart fern watering schedule.

Signs you are over-feeding wart fern

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for wart fern:

Signs you are under-feeding wart fern

If the symptoms point at watering, light or roots rather than nutrition, the full wart fern care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

Flush the pot of wart fern with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.

Organic vs synthetic feeds for wart fern

Organic options

A diluted seaweed or worm-casting feed, or fish emulsion if you can tolerate the smell indoors. UK: Westland or Baby Bio Organic, dilute seaweed; US: Espoma Indoor! or Neptune's Harvest fish & seaweed. Slow, gentle and hard to overdo.

Synthetic / liquid feeds

A general-purpose houseplant liquid at half strength — UK: Baby Bio, Westland Houseplant Feed or Phostrogen; US: Miracle-Gro Indoor Plant Food or Schultz. Convenient and fast-acting; the only risk is overdoing it.

Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.

Fertilising wart fern — frequently asked questions

What fertiliser does wart fern need?

A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula. Wart Fern is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.

How often should I feed wart fern?

Feed monthly through spring and summer with a balanced liquid fertiliser diluted to half strength. Ferns are salt-sensitive, so flush the mix occasionally and pause feeding in autumn and winter. Feed monthly through spring and summer with a balanced liquid fertiliser diluted to half strength. Ferns are salt-sensitive, so flush the mix occasionally and pause feeding in autumn and winter. Treat that as monthly between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.

What strength of feed for wart fern?

Half strength is the safe default for wart fern — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.

What does over-feeding wart fern look like?

Brown, crispy leaf tips and edges with no sign of underwatering. A white, crusty salt deposit on the soil surface or pot rim. Weak, pale, stretched new growth that flops. Lower leaves yellow and drop while the soil is correctly watered. Feeding wart fern year-round on a fixed schedule, including dark winter months, is the most common mistake — it cannot use the nutrients in low light and the surplus simply burns the roots and crusts the soil.

Should I flush the soil of wart fern?

Flush the pot of wart fern with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.

Keep reading