Weeds in gravel driveways are easier to kill than you might first suspect. Home remedies may be the best way, as they are less expensive than commercial products, effective and don't involve dangerous chemicals.
Vinegar and Rock Salt
Vinegar and rock salt both kill plants indiscriminately, according to the website PlantCare. As all plants in gravel driveways are typically undesirable--and thus unnecessary to avoid--these may be great solutions. Salt, in particular stays in the soil and high levels of it render the earth unsuitable for growing plants--making it more likely weeds will stay away. Saturate roots with vinegar and/or pour enough rock salt on the base of the plant to saturate the soil.
One teaspoon of rubbing alcohol mixed with one litre of water makes an easy weed-killing spray. Spray the roots and plants with the solution.
Keeping Weeds Away
Creating physical barriers helps keep weeds at bay. Once the weeds are gone, completely cover the area in a layer of gravel. Also consider placing plastic sheeting under the gravel to give the driveway added protection.