Photo: Walter Siegmund (talk), CC BY-SA 3.0 · source

Water or marginal plant · Phrymaceae

Monkeyflower

Erythranthe guttata

In other languages: Gele maskerbloem (Nederlands) · Mimule tacheté (Français)

Monkeyflower is a perennial from western North America, where it grows along streams, springs and wet banks. In western Europe it has long since become naturalised along streams and rivers. It forms loose clumps 30–40 cm high, with soft, rounded leaves and hollow stems that root easily wherever they touch wet ground. From June into September it bears large, bright yellow two-lipped flowers with red spots in the throat, like a little mask. Gardeners love it because it brings months of colour to the pond edge and settles quickly in any wet soil. In nurseries it is often still sold under its old name, Mimulus guttatus.

Caution: A non-native plant that self-seeds readily and spreads from stem fragments; in western Europe it has already become naturalised along streams. Keep it in a garden pond with no connection to a stream or ditch, remove spent flowers and never throw plant waste into natural waters.

Updated on 9 October 2026

Light
Sun or partial shade
preferably some sun
Moisture
Moist to wet
must not dry out
Legal basis
Loam, clay or peat
any pH
Hardiness
Fully hardy
down to -20 °C
Size
0.4 m
tall, 0.4 m wide
Flowering
June–September

Key facts
Pruning months	March and July
Height	0.4 m
Native to Belgium	No, planted
Good for bees, butterflies and birds	Yes, for bees
Poisonous to people and pets	Not known to be poisonous
Flowering	June–September

Identify

Monkeyflower: how do you recognise it?

Habit: Loose clump 30–40 cm high and wide, with hollow, partly sprawling stems that root at the nodes.
Leaves: Round to oval, irregularly toothed and opposite; fresh light green and slightly fleshy.
Flowers: Two-lipped trumpets of 2–4 cm in loose sprays at the stem tips, from June to September.
Colour: Bright yellow, with red to reddish-brown spots in the throat and on the lower lip.
Roots: Shallow and fibrous, with runners that creep over wet ground and through shallow water.

Flowering: June–September · Plants: April–June · Pruning: March and July

In your garden

Why grow it?

Flowers for four months, from June into September, with eye-catching bright yellow blooms.
Thrives where many plants give up: in wet, boggy ground and even in shallow water.
Bumblebees and other bees visit the flowers; the red spots guide them to the nectar.
Hides the hard edge of a pond or stream under a soft green fringe.
Establishes quickly and fills an empty spot on the bank in a single season.

Monkeyflower: where does it grow best?

Sun or partial shade; it flowers most freely in sun, as long as the soil stays wet.
Wet soil at the pond edge or beside a stream: loam, clay or peat, acid to chalky.
Marsh zone: from the wet bank down to no more than 5 cm below the water surface.
Must never dry out: in an ordinary, dry border it shrivels in summer.
Allow 30–40 cm per plant; it looks best in a group of three to five.

Light: Sun and partial shade
Soil type: Loam, clay or peat
Acidity: Not fussy
Moisture: Wet
Size: 0.4 m tall, 0.4 m wide
Hardiness: Hardy (to -20 °C)

Goes well with

Marsh marigold: Flowers as early as April in the same wet conditions, so the bank gets colour sooner.
Water forget-me-not: Sky blue beside the bright yellow, in the same shallow zone.
Yellow flag iris: Tall, sword-shaped leaves as a backdrop at the pond edge.
Purple loosestrife: Purple spikes in July–August and a feast for bees and butterflies.
Water mint: Scented leaves and small lilac flowers in the same wet zone; keep it in a basket, though.

Maintenance

Monkeyflower: when and how to plant it?

Plant in April–June.

Plant from April to June, once the water has warmed up a little.
Use an aquatic basket filled with low-nutrient aquatic compost or heavy garden soil, with no potting compost or fertiliser; on the bank, simply plant into the wet soil.
Set the plant at the same depth as it was in its pot, firm it in well and top the basket with a layer of gravel so the soil does not wash out.
Place the basket so that the soil surface is no more than 5 cm below the water.
Space plants 30–40 cm apart.
On the bank: water in thoroughly straight away and keep the soil wet for the first few weeks.

Care

Water level: Keep the base wet at all times. If the level drops in summer, top up with rainwater.
Feeding: Not needed: extra nutrients in a pond feed algae. On the bank, a little compost in spring is enough.
Spent flowers: Cut off faded flower sprays: this gives new flowers and fewer seedlings.
Cutting back: After the first flush of flowers in July you can cut the plant back by half; it soon regrows and flowers again.
Renewing: Plants are often short-lived. Keep a few young seedlings or rooted stems as replacements.

Tip: Cut the plant back by half in July after the first flowers: within a few weeks it will be covered in blooms again.

Monkeyflower: when to prune it?

Pruning months: March and July.

When: Cut back in July after the first flush of flowers, and clear away dead stems in March.

How:

In July, shorten the faded stems by half, just above a few leaves.
Remove spent flower sprays before they set seed, especially if your pond is close to a stream or ditch.
In March, remove old, dead stems at the base before the new shoots appear.
Pull out runners and seedlings that spread too far.

Caution: Do not let it seed into a stream or ditch that flows on elsewhere: that is how it spreads into the wild.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Cuttings: From May to August: cut 8–10 cm stems and push them into wet soil or simply stand them in a glass of water. They usually root within two weeks.
Division: In April–May, split a clump or sever a rooted runner and replant it elsewhere.
Self-sown seedlings: It seeds itself freely on wet ground. Move young seedlings in spring to where you want them.

Monkeyflower: how does it get through the winter?

Hardy to −20 °C.

Hardy to about −20 °C: it survives a normal Belgian winter without protection.
Leave the dead stems until March: they protect the crown of the plant.
After a cold, wet winter an old plant sometimes dies anyway; seedlings and rooted cuttings then take its place.
In a small tub everything can freeze solid: move the tub against a sheltered wall in winter.

Diseases and pests

Slugs: They eat holes in young leaves in spring. Pick them off in the evening; frogs and toads lend a hand.
Powdery mildew: White powder on the leaves, especially when the soil gets too dry. Keep the base wet and cut off affected stems.
Aphids: On young shoots and flower buds. Hose them off with water; ladybirds do the rest.
Too many seedlings: It self-seeds readily. Remove spent flowers in good time and weed out unwanted seedlings.
Bare, untidy plant: After summer the stems become long and open. Cutting back in July and young cuttings as replacements keep it fresh.

Through the year

March: Cut dead stems back to the base.
April: Plant or divide. Watch out for slugs.
May: Plant. Take cuttings.
June: Flowering begins. Planting is still possible until the end of June.
July: After the first flush, cut back by half.
August: Second flush of flowers. Top up the water level in dry spells.
September: Last flowers. Remove spent sprays to prevent self-seeding.
November: Leave dead stems standing as winter protection.

Use

Good for wildlife

Bees: Nectar and pollen for honeybees and wild bees.

You and this species

Did you know?

The stigma has two lobes that snap shut when an insect touches them, so the pollen it has brought stays firmly in place.
In 2012 botanists moved this species from the genus Mimulus to Erythranthe; in the trade it is often still called Mimulus.
The name Mimulus comes from the Latin mimus, an actor: the flower looks like a mask or a grinning little face.

Garden plants · All species