Carduus nutans Seeds | Musk Thistle
LATIN NAME: Carduus nutans
COMMON NAME: Musk Thistle, Nodding Thistle
Plant Profile
Musk thistle is a tall, statuesque biennial of the daisy family, native to Europe and western Asia and now a widespread weed of pasture, roadsides and rangeland in North America, South America, Australia and New Zealand. It grows fifty to a hundred and eighty centimetres tall, with deeply cut, spine-edged leaves that have a pale midrib.
The large, purple-red flower heads nod to one side, giving the plant its other common name, and they carry a faint musky scent that is strongest in the evening. The rosette of the first year is broad and flat, and it can smother the grass around it before the stem ever appears.
Science & Biotechnology
Musk thistle is one of the best-documented cases of classical biological control. The weevil Rhinocyllus conicus was released in North America in 1969 to feed on the flower heads, and it reduced seed production substantially, but later studies found that it also attacked native thistles, which turned the programme into a cautionary tale about host-range testing.
Research since then has been far more careful about non-target effects, and the case is now taught in invasion biology courses. Work on the plant’s seed bank has shown that seed can survive in soil for a decade, so control has to be repeated for several years to be effective.
Uses & Benefits
The plant has essentially no garden value and is classed as a noxious weed across much of its introduced range, where it can dominate overgrazed pasture within a few seasons. Its story is more useful as a case study than as a garden plant.
Like other thistles, the young stems can be peeled and eaten, and the plant has a folk record as a bitter tonic, but it is not a species anyone should plant deliberately. The flowers are visited by bees and butterflies, which is the one argument in its favour.
In New Zealand it is a serious pasture weed, and dense stands reduce grazing capacity by half.
Growing from Seed
Sow in spring, five millimetres deep, at 15-20C; germination is quick and reliable. The plant forms a rosette in its first year and bolts in the second, producing a large seed crop.
It grows best in full sun on disturbed or overgrazed ground and tolerates poor soil. If it appears, cut the root below the crown or remove the heads before they ripen, since a single plant can produce thousands of seeds. Do not compost the heads, since the seed survives the heap.
The rosette is easy to spot in autumn, and that is the best time to remove it.
Seed heads should be bagged and binned, not left on the ground.
Cutting the stem below the crown kills the plant more reliably than cutting the top.
Our Take
Musk thistle is a plant to admire from a distance and to remove from pasture. Its history in biological control is more interesting than the plant itself.
Related Reading
Gardeners who grow Musk Thistle often pair it with these related subjects: