Question: After a heavy rain, water has pooled in the garden and a green film has grown on the wet dirt. Is this from over watering prior to the rain?
Answer: What you describe is harmless algae. It blooms when the soil is wet and warm and the sun is shining. When the soil dries out it will die out and/or you can cultivate or rake the soil to remove it from the surface.
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When singular and plural spellings differ, as in peony and peonies, try both.