Perennial Sowthistle Care

Sonchus asper, the prickly sow-thistle, rough milk thistle, spiny sowthistle, sharp-fringed sow thistle, or spiny-leaved sow thistle, is a widespread plant in the dandelion tribe within the daisy family. Despite the name, Perennial sowthistle resembles dandelions more than it does true thistles. Perennial sowthistle usually grows 2 to 4 feet high and has an extensive root system that grows up to 10 feet deep and can spread more than 6 feet in one growing season. It has erect, hollow stems with bitter, milky juice. Its leaves vary in size and are alternate, prickly edged, and lance shaped. Flower heads are 1 to 2 inches across and bright yellow. Its bracts are green with white margins and covered with tiny hairs.

Sonchus asper is an annual or biennial herb sometimes reaching a height of 200 cm. with spiny leaves and yellow flowers resembling those of the dandelion. The leaves are bluish-green, simple, lanceolate, with wavy and sometimes lobed margins, covered in spines on both the margins and beneath. The base of the leaf surrounds the stem. The leaves and stems emit a milky sap when cut. One plant will produce several flat-topped arrays of flower heads, each head containing numerous yellow ray flowers but no disc flowers.

This plant might be poisonous

How to get rid of: This plant is relatively resistant to many, but not all, common broadleaf herbicides. Spot spraying with an herbicide containing the active ingredient glyphosate (Roundup Pro, Glyfos, etc.) may be used effectively in the spring while the plant is actively growing, up to when the flowering stem bolts. The goal is to insure all plants have emerged. Cut the plant tops off before an herbicide application to prevent seed production, and spray each plant thoroughly on the stems and leaves, enough to be wet but not dripping. Be aware, glyphosate is non-selective and will injure any plants that it comes in contact with, including grass.