I never had hitchhikers on my plants until the last time I got plants about a month ago and now I have at least 2 ramshorns and at least one pond snail. They don't seem to be reproducing that fast. I've only seen the pond snail three times (It seems that it likes to stay in my filter), and the most number of ramshorns I've seen at once is 2. Maybe my bettas are eating them... The ramshorns are still really small, but the pond snail, who was the size of a sesame seed the first time I saw it is now the size of a pea.
Plus I have my two nerites, which I bought.