Soak the plants in a mild bleach solution for a two or three minutes.
My first tank had pest snails. I have since then deliberately added them to my two new tanks. I see very few snails because there is not much food around for them, which in a lot of cases comes from overfeeding fish. The few snails that my tanks manage to sustain are only eating detritus, which is a good thing in my opinion. I now have one Ramshorn snail in my first tank that is 1cm across, and I see him roaming around with four or five threads of algae hanging off his shell. IMO, he adds something to the tank, and is not an eyesore. I rarely see more than one or two snails at a time.
Dave.