User blog comment:Milesprower2/Top 15 Best and Worst Plants/@comment-1764483-20150105202800/@comment-4077536-20150106205105

It doesn't stack, but I think the reason everyone thinks it stacks is because Sap-fling may actually slow zombies more than Winter Melon does. I'm guessing that everyone tests Sap-fling by comparing a frozen and a frozen and sapped zombie, so the sapped one will be slower, but when you compare a sapped and frozen and sapped zombie, they move the same.