Creeping thistle (cirsium arvense) is an invasive, pernicious weed that is listed on the California Invasive Species List as Canada thistle. Its dense, green spikes form rosettes from which flower stalks grow in late spring to early summer. Numerous purple, brushlike flowers on each stalk produce uncountable seeds distributed by the wind. Creeping thistle grows along roads, in ditches and in underused open fields. It thrives in a broad range of Sunset's Climate Zones, from A1 to A3 and 1 through 24. The plant extends a huge root colony network that is nearly impossible to kill. Therefore, it is better to focus on control measures.
Cover the creeping thistle growth area with an opaque weed screen cloth or sheet of plastic. Cover every single plant and ensure light cannot reach them. Anchor the ground cover with large stones or landscape staples. Leave the cover on the ground for an entire growing season.
Wear heavy gloves and dig up the first young plants that appear in any area. The best remedy for creeping thistle is to prevent it from becoming established in the first place. Dig deep and remove all traces of roots. If you leave a root remnant, it will sprout a new plant. Never try to dig up an established colony of creeping thistle. It is virtually impossible.
Seal the discarded plants and roots in plastic bags. Leave the bags in the sun until the heat kills the plants inside.
Mow or cut off the flower stalks of creeping thistle several times a season before seeds form. For thick growth, a heavy-duty tractor mower is necessary. For low, thinner growth, use a regular lawnmower. This will not affect the established foliage, but it will prevent the seeds from producing new plants.
Things You Will Need
- Weed screen cloth or plastic
- Landscape staples
- Plastic bags
- Tractor mower or lawnmower
- Avoid using glyphosate herbicides or other poisons for creeping thistle control. Herbicides have little effect on this weed.
- Creeping thistle resembles a rare native thistle in the Yukon area of Canada called Elk thistle. Elk thistle is sometimes eradicated because it is mistaken for creeping thistle. But elk thistle has a larger flower head and grows in wet areas, whereas creeping thistle does not.
- The prickly leaves of creeping thistle can pierce the skin and cause pain. Always wear protective clothing when dealing with it.
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