St John's Wort — Grow Guide — Holly's Homestead

⇩ Download A4 PDF

St John's Wort is a declared noxious weed in parts of Victoria, NSW, the ACT, Tasmania, and WA — exact status varies by local council area, so check with your own council or state biosecurity agency before planting. Separately, if used internally, it has serious interactions with oral contraceptives, antidepressants, and other prescription medications; this guide covers growing it, not using it — speak with a doctor before any internal use.

Sun

Full sun

Water

Low, drought tolerant once established

Soil pH

6.0–7.5

Spacing

30–45cm

Depth

as per pot

01Two cautions before you plant

St John's Wort's star-shaped yellow flowers have a long history of traditional use, but this is a plant with strings attached — see the safety note above.

02Planting

Method

Plant from a nursery pot, or grow from seed (needs a cold period to germinate well).

Soil

Free-draining, moderately fertile.

Timing

Plant in spring or autumn.

Planting timing varies significantly by Australian climate zone. Set your zone above (or use the Find My Climate Zone tool) for guidance tailored to your own area.

03Growing care

Water moderately while establishing; one of the most drought-tolerant plants on this site once settled.
Deadhead spent flowers to extend the bloom period.
Cut back dead growth in late autumn once it dies down.
Divide congested clumps every 2–3 years to keep them contained and vigorous.

04Problems

Root rot — from poor drainage; ensure it's not sitting wet.
Spreading beyond the bed — the main risk, via both rhizomes and self-seeding; deadhead before seed sets and divide regularly.
Very few other pests — a hardy, easy-going perennial.
Powdery mildew — humid, crowded conditions; space well for airflow.

05Harvest & storage

Signs

Flowers ready once petals fully open, usually from the first season onward.

Method

Snip whole flower heads once fully open; leaves can be picked any time.

Curing

Air-dry flowers and leaves on a tray out of direct sun.

Storage

Dried flowers keep for months in an airtight container.

Preserving

See Dehydrating for ways to keep a surplus.

06Companions & rotation

Plant nearby

Best given its own contained spot, given its weed status

Avoid nearby

Areas bordering bushland or waterways, given its weed status

Rotation note

Not applicable — long-lived perennial, spreads by rhizome and seed.

St John's Wort is a declared noxious weed in parts of Australia — check local rules before planting. This guide covers growing it only, not using it.