Mimulus cardinalis - Scarlet Monkey Flower, Pond Marginal Plant (RHS A

Mimulus cardinalis (now listed as Erythranthe cardinalis), known as scarlet monkey flower, holds the RHS Award of Garden Merit. Through summer it carries scarlet, two-lipped flowers up to 5 cm long.

Scarlet monkey flower at a glance

Botanical name	Erythranthe cardinalis (syn. Mimulus cardinalis)
Common name	Scarlet monkey flower, cardinal monkey flower
Plant type	Short-lived perennial; dies back in winter
Height and spread	About 50–90 cm tall, up to 50 cm wide
Flowers	Scarlet, two-lipped, up to 5 cm long, over a long period in summer
Position	Full sun or part shade
Soil	Wet, humus-rich, poorly drained soil
Pond depth	0–10 cm of water over the crown
Hardiness	RHS H4 – hardy in an average UK winter (-10 to -5°C)
Native to	Western USA and Mexico (not UK native)

Where to plant scarlet monkey flower

A pond margin with up to 10 cm of water over the crown
Bog gardens with wet, humus-rich soil
Sun or part shade

Does it come back every year?

It is a perennial, but the RHS describes it as short-lived and it is often grown as an annual. It is rated H4, hardy through an average UK winter, so give it some winter protection in cold areas.

How to plant and care for it

Plant in spring. Deadhead to prolong flowering and cut back after flowering. Protect young shoots from slugs and snails, and watch for powdery mildew on young plants.

Which size should I buy?

Bare-root plants (7 cm, 9 cm, 1 litre and 3 litre) arrive without a pot or compost and are the most economical way to plant a group. Potted plants (9 cm, 1 litre and 3 litre) arrive growing in our peat-free compost and give a faster display. Packs of 3 come in 7 cm, 9 cm, 1 litre and 3 litre bare-root sizes and cost less per plant. The 2x Pot & Compost option is two plants supplied with pots and compost.