Fertilising guide
How to fertilise Arum Lily (Zantedeschia aethiopica)— schedule & NPK
Also called Arum Lily, Calla Lily, White Calla, Pig Lily.
More about arum lily
About Arum Lily
Zantedeschia aethiopica · also called Arum Lily, Calla Lily · flowering
Zantedeschia aethiopica is a robust, rhizomatous perennial native to stream banks, marshes, and moist meadows in southern Africa, producing large, pure-white spathe flowers surrounding a yellow spadix from late winter to early summer. It thrives in moist to wet, humus-rich soil in full sun to part shade and can be grown as a marginal aquatic with roots in shallow water. In the UK it is hardy enough to overwinter outdoors in most areas with mulch protection; in colder climates (USDA zones below 8) lift rhizomes and store frost-free. All parts are toxic to cats and dogs.
Growth habit: Clump-forming, rhizomatous herbaceous perennial; evergreen in frost-free climates, dying back in cold winters and re-emerging vigorously from the rhizome in spring.
What fertiliser arum lily actually wants — and why
Arum Lily 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 arum lily: 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 arum lily, 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 arum lily:
Feed every 2–3 weeks from spring until flowering ends with a high-potassium liquid fertiliser (tomato feed is ideal) to support large, waxy flowers; stop feeding once foliage yellows in late summer. Treat that as sparingly through the growing season 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 arum lily 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 arum lily
Half strength is the safe default for arum lily — 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 arum lily first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the arum lily watering schedule.
Signs you are over-feeding arum lily
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for arum lily:
- 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.
Signs you are under-feeding arum lily
- Uniformly pale or yellow-green leaves, oldest first.
- Noticeably small new leaves and stalled growth in good light and season.
- A generally tired, lacklustre look despite correct watering and light.
If the symptoms point at watering, light or roots rather than nutrition, the full arum lily care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of arum lily 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 arum lily
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 arum lily — frequently asked questions
What fertiliser does arum lily 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. Arum Lily 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 arum lily?
Feed every 2–3 weeks from spring until flowering ends with a high-potassium liquid fertiliser (tomato feed is ideal) to support large, waxy flowers; stop feeding once foliage yellows in late summer. Feed every 2–3 weeks from spring until flowering ends with a high-potassium liquid fertiliser (tomato feed is ideal) to support large, waxy flowers; stop feeding once foliage yellows in late summer. Treat that as sparingly through the growing season 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 arum lily?
Half strength is the safe default for arum lily — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding arum lily 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 arum lily 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 arum lily?
Flush the pot of arum lily 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
- Arum Lily care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water arum lily — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise western bog laurel
- How to fertilise scarlet leucothoe
- How to fertilise coastal leucothoe
- All 10153 fertilising guides in the Growli library