Answer: If you don't regularly deadhead the spent flowers, what you're finding might very well be seeds; look for opened seed pods still attached to the stems of the plants. These will be either brown or tan and still attached to the stems where flowers once were. Seeds of petunias and about the size of a grain of salt and a dark brown. Another possiblity is frass (bug poop). If the leaves of your plants have holes eaten in them, the caterpillars feeding on them may have left some excrement. Inspect your plants very closely for signs of insect pests to rule out the possibility of frass. If caterpillars (little green worms) are feeding on your petunia plants, you can control them with Bt (sold as Dipel). Best wishes with your garden!
Q&A Library Searching Tips