I would suggest taking a large sample of soil to your local extension office and have them test it for you. They will tell you exactly what amendments to add. I fertilized the heck out of my soil to ensure it was acidic enough. My blueberries started turning chloritic... When plants turn chloritic, it means SOMETHING is out of whack. But when I search online, I kept seeing "advice" that told me it was because the pH was too high. So I'd add more sulphur. Well....when the results of my soil testing came back, this is what it said:
Soil pH: 3.8
Phosphorus: 256 ppm
Potassium: 191 ppm
Zinc: 4.3 ppm
Optimum for Blueberries:
Soil pH: 4.5 - 5.5
Phosphorus: 36-50 ppm
Potassium: 131-175 ppm
Zinc: 4.1 - 8 ppm
So, as you can see, I nuked my blueberries without realizing what was happening in the soil. I got those test results back in early July last year. By that point, it was too late to save anything, I think. I stopped amending the soil immediately. I wasn't sure what to do to make it better so I figured I'd let it sit and naturally readjust. I lost 6 out 7 of my blueberry bushes. Only 1 survived.
Before I plant the 2 new ones I got, I will get the soil tested again to make sure it is right. Very expensive mistake on my part.... Oh, and btw, if you DO get your soil testing....make sure you have AT LEAST 2-4 cups of soil from each bed where you want to plant. Label them appropriately so you can tell them apart. This was another mistake I made because I didn't have ENOUGH soil to be tested the first time I took it in.