deck's surface and using a stiff brush to work it into the wood, making sure to work in the direction of the grain at all times.  After about an hour, it should have taken effect, and you'll be able to remove it with cool water without worrying about it harming nearby plants.  A final, alternative way to achieve this highly sought after weathered look is to treat your decking with liming wax, but this is a costly process and not for the feint hearted.