Fertilising guide
How to fertilise Caltha palustris (Caltha palustris)— schedule & NPK
Also called Marsh Marigold, Kingcup, May Blobs.
More about caltha palustris
About Caltha palustris
Caltha palustris · also called Marsh Marigold, Kingcup · flowering
Caltha palustris is a cheerful early-spring bog perennial in the buttercup family, forming mounds of glossy, kidney-shaped leaves topped with waxy, golden-yellow cup flowers. A native of wet meadows, ditches and pond margins, it lights up the waterside in March to May and is a magnet for early pollinators.
Growth habit: Clump-forming herbaceous perennial with mounded glossy foliage and upright flowering stems. Goes semi-dormant and may die back in summer heat, returning each spring.
What fertiliser caltha palustris actually wants — and why
Caltha palustris 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 caltha palustris: 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 caltha palustris, 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 caltha palustris:
Light feeder in rich wet soil. A spring mulch of well-rotted organic matter or one balanced slow-release feed is plenty; in nutrient-rich pond mud, supplementary feeding is usually unnecessary. 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 caltha palustris 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 caltha palustris
Half strength is the safe default for caltha palustris — 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 caltha palustris first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the caltha palustris watering schedule.
Signs you are over-feeding caltha palustris
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for caltha palustris:
- 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 caltha palustris
- 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 caltha palustris care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of caltha palustris 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 caltha palustris
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 caltha palustris — frequently asked questions
What fertiliser does caltha palustris 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. Caltha palustris 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 caltha palustris?
Light feeder in rich wet soil. A spring mulch of well-rotted organic matter or one balanced slow-release feed is plenty; in nutrient-rich pond mud, supplementary feeding is usually unnecessary. Light feeder in rich wet soil. A spring mulch of well-rotted organic matter or one balanced slow-release feed is plenty; in nutrient-rich pond mud, supplementary feeding is usually unnecessary. 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 caltha palustris?
Half strength is the safe default for caltha palustris — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding caltha palustris 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 caltha palustris 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 caltha palustris?
Flush the pot of caltha palustris 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
- Caltha palustris care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water caltha palustris — 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 peace lily
- How to fertilise bird of paradise
- How to fertilise hoya
- All 5561 fertilising guides in the Growli library