Coffee grounds acidify soil.
Coffee grounds haven't been shown to reliably lower soil pH, so they won't durably acidify your soil or make it blueberry-friendly. Put them in the compost, where they feed soil life; to lower pH, use elemental sulfur guided by a soil test.
What is actually known
Coffee grounds have not been shown to consistently lower soil pH, so they will not durably acidify soil to blueberry range. They make a good compost input, carrying carbon and nitrogen that feed soil organisms. To actually lower pH, use elemental sulfur guided by a soil test.
The evidence
Evidence: checked against 1 source in the research-based literature.
The source
Coffee grounds can be beneficial to your soil. However, they have not been shown to consistently lower soil pH.
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Milpa Gardens. “Coffee grounds acidify soil.” Evidence grade: Contested. https://milpa.garden/beliefs/coffee-grounds-acidify-soil/
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