HoneyHQ

Yellow starthistle

Centaurea solstitialisAsteraceaeAnnual

A Mediterranean thistle relative that has become one of California's most damaging invasive weeds and, simultaneously, one of its most valuable honey plants — the source of the pale, tangy star thistle honey sold across the western United States. Very few plants present the conflict between a good honey crop and a serious ecological problem as starkly.

Where not to plant it

One of the most damaging invasive weeds in the western United States, occupying millions of hectares of rangeland, displacing native flora, depleting soil moisture with a deep taproot, and rendering pasture unusable through its spines and its toxicity to horses. It is simultaneously a first-rate honey plant, and the honest position is that both facts are true and the ecological cost outweighs the honey. It should not be planted anywhere.

Caution

Yellow starthistle is toxic to horses, causing an irreversible neurological condition known as chewing disease. This is a real hazard on grazing land and is a substantial part of the case for controlling it.

Value to bees

Nectar
Very high
Pollen
Moderate
As a honey crop
Major honey crop — yields a surplus in good years
Which bees, and why
Worked heavily by honey bees during a season when little else is flowering, which gives it real value to beekeepers and complicates the case for eradicating it.
Worth knowing
An outstanding summer nectar source in a season when Californian forage is otherwise very thin.

Flowering

In flower
June to September (northern hemisphere)

Flowers through the driest part of the Californian summer, when almost nothing else does — which is precisely why it matters to beekeeping there.

When nectar flows
Heavy and remarkably persistent through summer drought, sustained by a taproot reaching well below the surface.
Year-to-year variation
Reliable, which is unusual for a Californian honey crop, because the plant flowers through the dry season on deep roots. The uncertainty is not the weather but weed control programmes.

What it does to the honey

Very pale, almost water-white, with a clean sweetness and a distinctive tangy, faintly resinous finish. It is slow to crystallise and highly regarded.

Growing it

Conditions
Full sun on dry ground, and adapted to Mediterranean-climate summers. It requires no encouragement whatsoever.
Size
30-100 cm tall, occasionally to 2 m on good ground.
Native range
The Mediterranean basin and western Asia. Introduced to California in the 1850s in contaminated alfalfa seed and now covering millions of hectares of the western United States.
Suits
Farm scale

What it looks like

A grey-green branching annual with narrow winged stems and bright yellow thistle-like flower heads, each surrounded by long sharp straw-coloured spines that give the plant its name.

Sources

  • HoneyHQ editorial synthesis — HEKNO Ltd · HoneyHQ synthesis
  • Assessment Report on Pollinators, Pollination and Food Production — Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) (2016) · Systematic review Link

How sources are selected and weighted is set out in the sources and evidence policy.

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