Canada thistle, also known as creeping thistle, is one of the most troublesome of weeds. It is native to Europe and Asia but now grows across most of the northern United States and southern Canada. The thistle has prickly leaves and small pink, purple, or white flowers.
The weed annoys farmers because it grows in cultivated areas as well as in wasteland and is hard to control. It spreads easily because new plants can grow from bits of the roots of old plants. If a plant is only partly uprooted, several plants can still grow from its remaining roots. One way to destroy the plant is to kill its roots through starvation. The leaves supply the food that keeps the roots alive. This food supply can be cut off by cutting down the green stems of the plant as soon as they appear. This method can be combined with the growing of crops, such as corn, that require cultivation between rows. Cultivation brings the thistle seeds nearer the surface so they may start growing. Later, the stems are cut down. Chemical weedkillers are also used to destroy the plant.
