Canada Thistle

Canada Thistle

Canada thistle is an herbaceous perennial with upright, grooved, hairy stems that branch near the top of the plant. It grows 2-6.5' tall. It is legally classified as a noxious weed.

Leaves:

Simple; alternate; lance-shaped; tapering; irregularly lobed; with spiney, toothed edges; stalkless; green on both sides; smooth when young but becoming hairy or downy with maturity.

Flowers:

Numerous, small (0.5-0.75" wide), purple to pink (rarely white), terminal flower heads. Blooms June-September. Seeds are often spread by mowing after flowering has begun. It produces taproots that may grow more than 6' deep. Readily regenerates from root fragments.

Control:

*Manual/Mechanical: Rull or mow (minimum 3 times per growing season) decrease root reserves; mow when flower buds are just about to open. Late spring (May-June) burn for 3 consecutive years stimulates germination and kills seedlings.