The most common thistle, Canada thistle weed, is an invasive plant. These plants reproduce from their roots and their seeds. Seeds buried in the soil can survive for more than 10 years. These plants are characterized by extensive spreading root systems and small flowering heads. They survive best in cooler temperatures with moist soil and sunny locations. These same conditions are found in most home gardens.
Thistles in the home garden can be harmful to your plants, taking up valuable nutrients and space. If you are concerned about using herbicides in your garden, alternatively you can use a rototiller for thistle removal.
Remove thistles from soil anytime you see them. Use a shovel to dig underneath the thistle, loosen and remove the plant completely.
Clip flower heads directly below the head from thistle plants that have bloomed to prevent the spreading of seeds. Dispose of flower heads in trash.
Use rototiller on mature thistles that are harder to remove or if the infestation covers a large area. Till soil 6 to 8 inches deep, working slowly, digging with rototiller until soil loosens and then proceed to the next section. Remove thistles completely after they are loosened enough to pull. Tilling may need to be done once a month until all thistles appear to be removed--when there is no apparent regrowth.
Rake any remains of thistles into a pile and dispose of in trash.