Grow Guide for Marsh Marigold (Caltha palustris)

🌼 Marsh Marigold – Caltha palustris

Family: Ranunculaceae
Common Names: Marsh marigold, Kingcup, Cowflock, May blob
Botanical Synonyms: Caltha palustris var. radicans, Caltha palustris var. palustris

🔬 Botanical Description

Marsh marigold is a robust, herbaceous perennial native to temperate regions of Europe, Asia, and North America. It thrives in wetlands, fens, damp meadows, and shallow water margins.

Habit: Clump-forming, with hollow, branching stems
Height: Typically 30–60 cm
Leaves: Glossy, kidney- or heart-shaped, with scalloped margins
Flowers: Bright yellow, buttercup-like, 2.5–5 cm across; not true petals but petaloid sepals
Bloom Time: March to May, often with a second flush in autumn
Fruit: A cluster of follicles containing black seeds

🌍 Position & Growing Conditions

Light: Full sun to part shade
Soil: Consistently moist to wet, humus-rich, slightly acidic to neutral (pH 5.5–7)
Moisture: Thrives in wet soil or shallow standing water up to 10 cm deep
Location: Ideal at the edge of ponds, bog gardens, or stream margins

If your soil is too alkaline and you’re planting in the ground (not in a pond basket), you can:

Add ericaceous compost
Incorporate leaf mould or pine needle mulch
Use sulphur chips or iron sulphate to gradually lower the pH

🌡️ Temperature & Hardiness

Hardy in RHS Zones: H7 – very hardy, tolerates temperatures down to -20°C or lower
Climate Suitability: Perfect for the UK and other temperate zones
Frost Tolerance: Fully frost-hardy; dies back in winter and regrows in spring

🛠️ Care & Maintenance

General Care:

Cut back old foliage in late autumn or early spring before new growth appears
Remove spent flowers to encourage a second flush (optional)
Divide congested clumps every 3–5 years to maintain vigour

Feeding:

Not usually required if planted in fertile soil or aquatic planting media
Can benefit from a spring mulch of compost or leaf mould around the crown

Pests & Diseases:

Generally pest-free
Slugs may nibble young shoots, but damage is rarely serious
Avoid waterlogged, stagnant conditions to reduce risk of rot

✂️ Pruning

When: Late autumn (after flowering) or early spring
How: Cut back stems to ground level before new growth emerges
Optionally deadhead in spring to prolong bloom

🌱 Propagation

Division:

Best method for reliable results
When: Spring or autumn
How: Lift clumps, tease apart rooted sections with several shoots, and replant immediately

Seed:

Sow fresh seeds in autumn or early spring
Requires moist conditions and light for germination
May take 1–2 years to flower from seed

💧 Planting in a Pond or Bog Garden

In a Pond:

Plant in aquatic baskets filled with loam-based compost (e.g., John Innes No. 2)
Top with gravel to prevent soil washing out
Position at the pond margin (shelf) with crown just above water, up to 10 cm deep
Weigh basket with stone if necessary to keep stable

In a Bog Garden:

Ensure permanent moisture—ideal with a liner or where water collects naturally
Plant directly into the soil, spaced 30–40 cm apart
Mulch annually to maintain soil condition

🌸 Garden Uses

Wildlife ponds (attracts pollinators and amphibians)
Bog gardens and damp meadows
Naturalising in shady, wet areas
Pairs well with Iris pseudacorus, Primula japonica, and Ligularia species

⚠️ Toxicity

All parts are mildly toxic if ingested raw; contains protoanemonin
Sap may cause skin irritation in sensitive individuals—wear gloves when handling