Musk thistle is a biennial, meaning its life cycle is two years long. It can grow up to 10 feet tall where moisture and nutrients are plentiful. The flower, a striking dark purple color, measures from 1 1/2 to 3 inches across. The leaves are dark green and usually shiny. Musk thistle is also called nodding thistle because the flowers are so heavy that they tend to bend over on their stalks.

Musk thistle in the high country is at full flower right now and beginning to produce seed. This is the best time to remove flowers before the seed escapes. Rosettes should also be removed, or they will make flowers and produce seed next year.

Biennial plants are much easier to control than perennials. When present in small numbers, digging up the plant at least two inches below the soil can eliminate musk thistle for good.

There are many native thistles in the area – some of them rare or uncommon. When removing thistle, please make sure it is an invasive species and not a native plant. Note: no native thistles have dark purple-colored flowers.

For more information please contact the County Weed Program at 327-0399 or email Sheila Grother at sheilag@sanmiguelcounty.org.