getting rid of weeds in a patio

You need to pull up the entire root of a perennial weed if you don't want it to come back, but that's difficult to do between patio stones.

Instead, pull off the top of the weed, and pour boiling water on the root.  You may need to do this a couple times to entirely kill the root.

This works in the garden too, but make sure not to get the boiling water too close to any plant you want to keep!!