Friday, June 13, 2014
Nuttall's Thistle - Cirsium nuttallii
Thistles are biennials; they do not flower in their first year, but develop a deep taproot and a basal rosette of leaves. Flowering occurs in the second year, they go to seed, and then the plants die. The large number of seeds produced by their parents, however, ensures that more plants will emerge next spring.
Nuttall's thistle is a robust, lanky species that reaches a mature height of 5 feet or more. The basal leaves are more narrow than in purple thistle, but they are equally armed with numerous sharp spines. In fact, the entire plant is exceedingly spiny.
A great many flower heads are produced atop the stems in summer. These too are much narrower than in purple thistle. The flowers vary in color from nearly white to a more common light pink. Plants remain in flower for many weeks, and as with other thistles, they are exceedingly attractive to pollinating insects.
Though thistles are wonderful plants for pollinators, they are extremely difficult to control in a landscape garden. Their thorniness makes working with them a challenge and the fact that they need to reseed to persist means that they need to be left alone until the seeds are dispersed. By then, you may have hundreds of seedlings germinating in every corner of your landscape (and in those of your neighbors). In many Midwestern states that I have lived in, growing thistles in a landscape is prohibited because they can be invasive.
If you have a more naturalistic setting and wish to add this species, despite its drawbacks, it is easy to propagate from seed collected when mature ("fuzzy"). This species is not currently available from commercial sources. Use it in out-of-the-way locations, away from pathways and trails and be prepared to weed out seedlings that appear in locations where they are not desired. Weed them when very small, when they are less well armed by thorns. Nuttall's thistle does well in partly sunny areas, but also can be grown in full sun.