Growli
Let's go

Fertilising guide

How to fertilise Button fern (Pellaea rotundifolia)— schedule & NPK

Also called New Zealand button fern, tarawera.

About Button fern

Pellaea rotundifolia · also called New Zealand button fern, tarawera · houseplant

Button fern is a small evergreen from New Zealand and Australia with round dark green leaflets on wiry stems. More drought-tolerant than most ferns and pet-safe. Good for terrariums and small pots.

Pellaea rotundifolia, native to New Zealand and Australia where, unusually for a fern, it grows in rocky, comparatively dry habitats rather than damp forest floor.

Feed sparingly with a dilute balanced fertiliser in the growing season; this compact, slow fern is easily over-fed.

Growth habit: Compact clumping fern

Watch for — Pale colour: Insufficient light or hungry — feed lightly.

Sources: rhs.org.uk, gardenia.net

What fertiliser button fern actually wants — and why

Button 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 button 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 button 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 button fern:

Quarter-strength balanced feed every 6-8 weeks in growing season. Treat that as every 6-8 weeks 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 button 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 button fern

Half strength is the safe default for button 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 button fern first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the button fern watering schedule.

Signs you are over-feeding button fern

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

Signs you are under-feeding button fern

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

Flushing and leaching the salts

Flush the pot of button 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 button 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 button fern — frequently asked questions

What fertiliser does button 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. Button 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 button fern?

Quarter-strength balanced feed every 6-8 weeks in growing season. Quarter-strength balanced feed every 6-8 weeks in growing season. Treat that as every 6-8 weeks 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 button fern?

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

What does over-feeding button 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 button 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 button fern?

Flush the pot of button 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