Answer: It takes a while, but peat moss will acidify the soil. You can work some into the soil beneath the plant, then add 2-3" as a top dressing. As the peat weathers and decomposes it will help acidify the soil. Make this an annual ritual and you'll eventually get the pH down to where blueberries like it (4.5 to 5.5) Generally the soil in the Pacific Northwest is on the acidic side - I'm surprised you have neutral soil!
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