Answer: The answer will depend on the variety of marigold you grow and its mature size, as well as the "look" you prefer. If the variety you plant matures at an average width of 12 inches, then plant them 12 inches apart on center for coverage of appriximately edge to edge. If you like to see soil between the individual plants, then plant them a bit further apart. If you like a very full look, plant them a little closer together. Marigolds cover a wide range of sizes from quite tiny to two feet across, so check the description of the one you plant.
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