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Herb · Hypericaceae

St John’s wort

Hypericum perforatum

In other languages: Sint-Janskruid (Nederlands) · Millepertuis perforé (Français)

St John’s wort is a native perennial of sunny verges, dry grassland and woodland edges across almost all of Europe and western Asia. From a creeping rootstock it sends up sturdy, upright stems of 30–60 cm with small, opposite leaves. From June to August, around St John’s Day on 24 June, it carries clusters of bright yellow flowers whose petals have tiny black dots along the edge. Hold a leaf up to the light and you will see dozens of translucent dots: this is why it is called perforatum, ‘perforated’. It is easy, tolerates drought and is popular with bees and bumblebees, which collect its pollen.

Caution: When eaten, and in some people also after contact with the sap, the plant makes the skin sensitive to sunlight, causing red patches or blisters. Grazing animals such as horses, cattle and sheep are most at risk; do not plant it in or next to a field. Keep young children and pets away and wear gloves. Do not use it on your own initiative: it can affect how medicines work. It self-seeds readily and is an invasive species in North America and Australia.

Updated on 9 October 2026

Light
Sun or partial shade
preferably some sun
Moisture
Dry to normal
no wet feet
Legal basis
Sand, loam or clay
any pH
Hardiness
Fully hardy
down to -30 °C
Size
0.6 m
tall, 0.4 m wide
Flowering
June–August

Key facts
Pruning months	March and September
Height	0.6 m
Native to Belgium	Yes
Good for bees, butterflies and birds	Yes, for bees
Poisonous to people and pets	Yes, take care with children and pets
Flowering	June–August

Identify

St John’s wort: how do you recognise it?

Habit: Upright perennial, branched at the top, 30–60 cm tall and about 40 cm wide, with a creeping rootstock.
Stem: Round, with two distinct raised lines running along its length.
Leaf: Small, oval to oblong, 1–3 cm, opposite and stalkless, with translucent dots visible against the light.
Flower: Bright yellow, about 2 cm across, with five petals dotted black along the edge and a tuft of stamens; in clusters from June to August.
Fruit: Small capsules holding countless tiny seeds.
Sap: Rub a flower bud or flower between your fingers and it stains them reddish purple.

Flowering: June–August · Sowing: April–May · Plants: April–May and September · Pruning: March and September

In your garden

Why grow it?

A long yellow display in high summer, from June to August.
Bees, bumblebees and hoverflies collect pollen from it.
Native and suited to a wildlife garden, a wildflower meadow or a dry border.
Drought-tolerant and happy in poor, stony soil.
A plant full of stories and folk customs around midsummer.

St John’s wort: where does it grow best?

Sun or partial shade; it flowers most freely in full sun.
Any well-drained soil: sand, loam or clay, acid to chalky; even poor, stony soil.
Dry to moist; it does not tolerate waterlogging.
Space plants 30–40 cm apart, preferably in a small group.
Do not plant it in or next to a field with horses, cattle or sheep.

Light: Sun and partial shade
Soil type: Sand, loam or clay
Acidity: Not fussy
Moisture: Dry or normal
Size: 0.6 m tall, 0.4 m wide
Hardiness: Hardy (to -30 °C)

Goes well with

Wild marjoram: Pinkish-purple flowers in the same sunny, dry spot, also loved by bees.
Ox-eye daisy: White flowers next to the yellow in a wildflower meadow.
Yarrow: Flat flower heads and fine leaves, just as drought-tolerant.
Common knapweed: Purple knobs that attract butterflies and bumblebees.
Viper’s bugloss: Blue spikes that set off the yellow beautifully.

Maintenance

St John’s wort: when and how to plant it?

Plant in April–May and September.

Plant in April–May or in September, when the soil is not frozen or waterlogged.
Dig a hole twice as wide as the pot; on heavy soil, mix in some coarse sand.
Set the plant at the same depth as in the pot.
Allow 30–40 cm between plants.
Water straight away and keep the soil lightly moist for the first few weeks.
Mulching is not needed; on dry soil a thin layer of gravel keeps weeds down.

Care

Water: Rarely needed once established: it tolerates drought well.
Feeding: Not needed: on rich soil the stems become floppy.
Spent flowers: Cut them off after flowering if you do not want it to self-seed everywhere.
Dead stems: If you leave them over winter, insects shelter in them; cut them down in March.
Gloves: Wear gloves when handling the plant, especially on sunny days.

Tip: Cut back the spent stems after flowering if you do not want it to self-seed everywhere. Never plant it in or next to a field: it is poisonous to horses, cattle and sheep.

St John’s wort: when to prune it?

Pruning months: March and September.

When: Real pruning is not needed. After flowering, in September, cut back the spent stems; in March, remove last year’s dead stems.

How:

In September, cut spent stems back to a few centimetres above the ground if you want to prevent seedlings.
If you leave them, it self-seeds and insects shelter in them over winter.
In March, remove the dead stems before the new shoots appear.
Chop off runners that spread too far at the edge with a spade.

Caution: Wear gloves when cutting back: the sap can make the skin more sensitive to sunlight.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed: Sow in April–May outdoors or in small pots, on the surface without covering: the seed germinates in the light.
Division: In spring or September, cut off a rooted piece from the edge of the clump with a spade and replant it elsewhere.
Self-sown seedlings: Seedlings appear by themselves around the plant; move them while young.

St John’s wort: how does it get through the winter?

Hardy to −30 °C.

Very hardy, to about −30 °C: no protection is needed in Belgium.
In winter, short leafy shoots remain at the base, from which it regrows in spring.
Wet, heavy soil in winter is a greater danger than frost.

Diseases and pests

Rust: Orange powdery pustules on the undersides of the leaves. Cut out affected stems and choose an airy spot.
Self-seeding: Seedlings all over the garden. Cut off the flowers after flowering and weed out seedlings while young.
Floppy stems: On soil that is too rich or too moist, the stems flop over. Do not feed and choose a poorer spot.
Root rot: The plant fades away on wet soil. Move it to a drier spot with good drainage.

Through the year

March: Cut down dead stems. Divide clumps.
April: Sow and plant.
May: Sow and plant.
June: Flowering begins around St John’s Day.
July: Full flower. Bees and bumblebees in the garden.
August: End of flowering. Collect seed.
September: Cut back spent stems if you do not want seedlings. Plant or divide.
October: Weed out seedlings where you do not want them.
November: Dormant.

Use

Edible and useful

Not edible. St John’s wort makes the skin sensitive to sunlight (in people and in grazing animals) and interacts dangerously with many medicines, such as the pill, blood thinners, antidepressants and heart and HIV drugs, making them less effective. Do not make your own tea or tincture to take, especially if you are on medication. Leave it in the garden for bees and butterflies. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Good for wildlife

Bees: Nectar and pollen for honeybees and wild bees.

You and this species

Did you know?

The translucent dots in the leaves are tiny oil glands; they give the plant its name perforatum, ‘perforated’.
Rub a flower between your fingers and they turn reddish purple from a red pigment called hypericin.
In California, St John’s wort became a pest of pastures. From the 1940s it was successfully brought under control there with small leaf beetles that live on the plant.

Garden plants · All species