Remove thistle weeds from a yard or garden by spraying them with a chemical herbicide or by removing them at their base with a pair of garden shears. Gardening Know How suggests spraying plants with herbicide on a sunny day when temperatures average between 65 F and 85 F for the best results. Avoid spraying herbicides on windy days, as they are non-selective and kill all vegetation they contact.
To treat thistle organically, Gardening Know How recommends cutting the plant as it appears at its base instead of removing the plant from the ground by pulling. Due to a thistle's extensive and rigorous root system, this method works the best because pulling often breaks the root and causes two plants to grow in its place. Check the location regularly and re-cut the thistle every time it appears so that it is eventually eradicated by the depletion of the plant's energy stores from continually re-growing its leaves.
Thistle does not thrive in healthy, fertile soils. For a thistle infestation, getting a soil test is a great way to identify a problem that could be causing an excess of this weed. Adding nutrients to the soil can minimize a thistle infestation and also help desired plants grow better.