Growing St John's Wort: The Complete Guide

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.

If you're thinking about adding St John's Wort to the homestead, here's the detail behind our printable guide — what it actually takes to grow it well in an Australian garden, not just the quick-reference version.

Every crop earns its place in a garden differently, and St John's Wort is no exception. At a glance, it's rated easy, with a sun of full sun; water of low, drought tolerant once established; soil ph of 6.0–7.5 — details that matter more once you're actually planning around them than they do on a first read. The rest of this article works through exactly what each of those means day to day, in more depth than a single printable card has room for, and with the reasoning behind each recommendation rather than just the recommendation itself.

Climate and Timing Considerations

St John's Wort is most at home in cooler, higher-rainfall areas above around 500m altitude \u2014 which is precisely why it's become a significant weed on the tablelands and slopes of NSW and Victoria specifically. Cool Temperate and Mediterranean zones (Tasmania, Melbourne, Adelaide, Perth) suit it climatically, but these are also the zones where its declared-weed status is most likely to apply, so checking local rules matters more here than for most other plants on this site. Warm Temperate and Subtropical zones (Sydney, Brisbane) can grow it too, though it's less naturalised in hot, humid conditions. Our site-wide zone setting adjusts the advisory note shown on the Planting Calendar for exactly this reason — worth setting once if you haven't already. The same zone setting also feeds the Harvest Calendar, so both ends of the growing cycle reflect wherever you actually garden, rather than a generic Australia-wide average.

• Cool Temperate & Mediterranean (TAS, Melbourne, Adelaide, Perth): the most climatically suited, and where its weed status is most likely to be relevant.
• Warm Temperate & Subtropical (Sydney, Brisbane): grows adequately, though less naturalised in hot, humid conditions.
• All zones: check your specific council or state biosecurity rules regardless of climate \u2014 declared status varies by local government area, not just by climate suitability.

Two 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 before deciding whether it belongs in your garden at all.

Getting St John's Wort Into the Ground

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.

These few details do most of the actual work, more than any single trick or shortcut would.

Day-to-Day Care

A few things matter most here:

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

These aren't equally important, but all of them are worth building into your routine — deadheading before seed sets is the single most important habit here, given how readily this plant spreads by seed as well as by rhizome. Treat this list as a routine to build rather than a one-off checklist, and it becomes second nature within a season or two.

What Can Go Wrong

The key things to get right:

• 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.

None of these are complicated on their own, but skipping one is a common source of trouble — given this plant's declared-weed status in parts of Australia, containing its spread is more than a tidiness issue here — see the safety note near the top of this article. Treat this list as a routine to build rather than a one-off checklist, and it becomes second nature within a season or two.

When and How to Harvest

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.

None of these are difficult individually — the value is in getting all of them right at once.

Preserving. See Dehydrating for ways to keep a harvest surplus.

Companions & rotation

Our printable card above lists specific plants that pair well nearby and others best avoided, along with a rotation note: best given its own contained spot, given its weed status. Getting this right matters more over multiple seasons than it does in any single one — the benefits and the risks of poor rotation both compound over time rather than showing up immediately.

Related Guides

If St John's Wort suits your garden, these related guides in our new Medicinal category are worth a look too:

• Aloe Vera
• Calendula
• Echinacea
• Lavender
• Lemon Balm
• Feverfew
• Yarrow
• Comfrey

That's the full picture behind St John's Wort. The printable A4 version of this guide — with the quick-reference gauges and diagram in one page — is available on the main guide page below. As with every guide on this site, this is general information based on our own research and experience, not professional, medical, or legal advice — the traditional uses mentioned above are noted for historical context, not as health claims, and its noxious-weed status varies by local government area, so always verify current rules with your own council or state biosecurity agency before planting.

Beyond the printable card, our Planting Calendar and Harvest Calendar tools will show a zone-adjusted note for St John's Wort specifically.

Frequently Asked Questions

→ View the printable A4 guide for St John's Wort