I was wondering if anyone had had luck with silk or plastic/rubber plant matter, which wouldn't rot away like the real thing.
Won't last a year if exposed to direct sunlight, especially at latitudes less then 35 degrees. Might last several years if shaded. In hot, dry climates, the natural plant materials will often last longer than the synthetic ones. Opposite in wet climates.
I know this thread is years old, but I have to completely disagree. I live N 29 and all of my plastic vegetation caches have lasted years. I buy green flower-arrangment foam, stick it to the container and shape it, stick whatever foliage you want on it, and glue it all down with liquid nail and top it with moss around the edges. I have one where SEVERAL cachers have trod on it and never known where the cache is. The only issue I have with the plastic foliage is fading-- each season I have to go out to the cache with the appropriate color of spray paint to match the surroundings.