Identifying invasives is an important step in managing your property and beneficial for the environment. Carduus nutans, the musk thistle, or nodding thistle is an invader that gardeners should remove immediately. This Eurasian native often gains a foothold in gardens and pastures before the property owner is aware of its presence. The musk thistle has become a troublesome pest at best and a noxious weed that takes over pastures and agricultural lands at worst. Many countries world-wide have it on their invasive plant lists and there are even laws on the books in some parts of the world that give a home-owner only 14 days to remove it if one sprouts on their property.
This biennial starts out with a rosette of spiny, prickly leaves the first year and the flower stalks with their distinctive, globe-shaped, purple flowers arise the second year and as a member of that vast Asteraceae tribe, the plant produces up to 120,000 seeds that float to new locations on downy fluff. In fact, there is a specific name for it, thistle down; and it was used to make paper in the past. These seeds can stay viable and dormant in the ground for 10 years or more, so it is important to remove the plants before they flower. There is an old Mother Goose rhyme that gives us a hint that thistles were a nuisance hundreds of years ago as well:
“If you cut thistles in May,
they will grow in a day
If you cut thistles in June,
that is too soon.
If you cut thistles in July,
then they will die.”
The rhyme was obviously created in a cooler northern European climate instead of my home in the southern U.S. since nodding thistles are currently mature and exploding their seeds along the roadways and pastures right now, but the warning is still applicable. Cut them below the ground, at the roots before they bloom.
The nodding thistle is so named because when the flowers mature, the heads droop. Most thistles in the Carduus genus hold the flowers upright on their stems, so this one is easy to identify. The flowers are also more globe-shaped, rather than the traditional thistle silhouette with the colorful tuft blooming from the top of the ovary, like Onopordum acanthium, the thistle associated with Scotland. But like its Scottish cousin, the stems and leaves are so thorny that livestock and creeping Norse invaders find they inflict painful wounds when accidentally stepped upon.
However, wildlife adore this plant. The fragrant flowers are an excellent source of nectar and pollen, so bees, butterflies and the occasional hummingbird all enjoy it. But the finch family of birds probably love it best. These thistles are in the Carduus genus and the finch genus is Carduelis and it is no accident that these names are so similar. Goldfinches in particular are especially fond of the seeds and are often seen perched on the seedheads enjoying a meal.
Humans have introduced biological controls in the past few years consisting of insects and a fungus specifically targeting thistles, however their influence is yet to make much of an impact. It is still best for property owners to promptly remove the plants to prevent a widespread invasion. Thistles can make a pasture or crop field unusable if left alone, so it is important to recognize this invader and take appropriate action when you find them.