The Cropsie Garden nursery where you water and hug a growing cropsie needs stars to hug it. It seems that those stars actually need to be new "blue" stars. That is, when replaying a level that you didn't get all three stars for, any more stars that you get than you did the previous times show as blue at the end when it shows the results of completing the level. The Cropsie Garden only accumulates these new blue stars for use in hugging Lucky. This should be stated in the help popup and/or by coloring the star blue in that game screen.
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