Ok will the grass be fondant or buttercream? If butterrea, use the tip. However, I recently read Debbie Brown's books and she suggests (for making fondant grass) that you roll out some green fondant then take the star tip (don't think it matters which one) and pressit down into the fondant slightly. Add a slight twist and lift up. this should create a grassy texture. Haven't tried it yet personally, but I'm anxious to see how it looks!