Getting it to bloom

Why won't my Double King Cup bloom? (and how to make it flower)

Also called Double King Cup, Double Marsh Marigold, Multiplex Kingcup (Caltha palustris 'Multiplex').

More about double king cup

About Double King Cup

Caltha palustris 'Multiplex' · also called Double King Cup, Double Marsh Marigold · flowering

Double King Cup is a striking double-flowered cultivar of the marsh marigold with densely packed, fully double rich-yellow flowers similar to 'Flore Pleno', listed separately by the RHS. Fully hardy (H7), it grows at pond margins and in shallow water up to 5 cm deep, producing an exceptional display of golden pompom blooms in early spring. A long-established cottage-garden and pond-margin favourite.

Plant type: flowering

Watch for — Powdery mildew on summer foliage: White powdery patches may appear on leaves in warm, dry or poorly ventilated conditions. Cut back the foliage hard immediately after spring flowering; the plant will regrow with clean leaves and the stress of summer heat is avoided as the plant is semi-dormant. Good airflow reduces recurrence.

The reasons double king cup isn't blooming

Almost every non-blooming double king cup traces back to one of these, roughly in order of how common they are:

Too little sun — most of these need full sun (or very bright light) to flower well; shade gives leaves, not blooms.
Too much nitrogen feed, driving lush foliage at the expense of flowers (very common with general or lawn feeds).
The plant has not been deadheaded, so it stops flowering once it sets seed.
Irregular watering — drought or waterlogging at the budding stage makes buds abort.
It is still too young or was checked by a transplant and is rebuilding before flowering.

Feeding double king cup a high-nitrogen general feed and growing it in too little sun — you get a big leafy plant and almost no flowers.

The fix — how to get double king cup to flower

Maximise sun. Give double king cup the sunniest spot you have — for most bedding and fruiting plants, more direct light directly means more flowers.
Switch the feed. Move off high-nitrogen feeds and use a higher-potassium "bloom" or tomato-type feed as it comes into flower.
Deadhead regularly. Remove spent flowers often to keep it producing more rather than stopping to set seed.
Water consistently. Keep moisture even through budding and flowering — drought-then-flood swings make buds drop.

Light and feeding do most of the heavy lifting here. Dial in the spot with the light guide for double king cup and get the feeding right with the double king cup fertilising schedule — the wrong feed (too much nitrogen) is one of the most common silent reasons a healthy plant makes leaves instead of flowers.

Bloom season and what to expect

Double King Cup flowers across its growing season (mostly summer) and, kept fed and deadheaded, can bloom for many weeks or right up to frost.

Post-bloom care so it flowers again

Deadhead, keep feeding lightly, and many will rebloom; collect seed from the best plants at the end of the season if you want to grow them again.

For everything else this plant needs day to day, see the full double king cup care brief and its watering schedule — a stressed, badly watered plant rarely has the energy to flower at all.

Double King Cup blooming — frequently asked questions

Why won't my double king cup flower?

Double King Cup blooms on the season's growth given enough sun, warmth and the right feed — there is no cold or photoperiod trick, just good growing conditions and a bloom-leaning feed. The most common reason it is not happening: Too little sun — most of these need full sun (or very bright light) to flower well; shade gives leaves, not blooms.

How do I make double king cup bloom?

Give double king cup the sunniest spot you have — for most bedding and fruiting plants, more direct light directly means more flowers. Move off high-nitrogen feeds and use a higher-potassium "bloom" or tomato-type feed as it comes into flower.

When does double king cup normally bloom?