Scotch thistle, known botanically as onopordum acanthiumas, is a species of cotton thistle in the aster plant family. Scotch thistle produces white or purple globe-shaped flowers from June through September. It is a biennial herb that grows in average- to poor-quality light soils that are wet. It readily naturalizes along roadways and open lands and is considered an invasive or noxious weed species in many states and regions.
Don a pair of heavy-duty gardening gloves such as those used by rose gardners. Scotch thistle produces spines that can be quite sharp all along its stems. Always wear gloves when working on or around the plant to prevent cuts and scrapes.
Cut back your scotch thistle in the late fall and/or early spring to remove any dead or damaged foliage and branches. Shear down to the crown with secateurs in the fall in climates where scotch thistle does not overwinter.
Water deeply in the fall to prepare the plant roots and surrounding soil for winter. Supplement winter rainfall as needed to keep the soil evenly moist throughout the fall and winter, never allowing the soil to dry out.
Mulch around the base of the plants with shredded bark or cocoa bean hulls to keep down competitive weeds and hold moisture to the soil.