Thistles, which are considered weeds, spread quickly and use up valuable nutrients in the lawn or garden. Canada, bull, milk, tall and musk are just a few thistle varieties that grow across the U.S. All thistles are tall, spiny plants that are typically killed with a commercial herbicide, such as one that contains 2,4-D or glyphosate. As a cheaper alternative, you can use bleach to kill your thistles since bleach kills any vegetation it comes in contact with.
Mix equal amounts of chlorine bleach and water into a spray bottle. For fewer spills, use a funnel to transfer the bleach to the spray bottle.
Spray the thistle heads, and work your way down to the roots. Do not get the bleach mixture on your grass, plants or other vegetation in the area; however, if you accidentally do, immediately wash it off with a hose, or wipe it off with a damp rag or sponge.
Reapply as necessary, such as when you see new thistles emerge. Use straight chlorine bleach if the treated thistles do not die within a week.