I grow blueberry shrubs here in Madison, Wisconsin, but all of our shrubs are planted in the ground, so my methods of pH control are not necessarily best for your situation. How are you measuring pH? If the leaves are deep green color, the shrubs are healthy, and pH must be reasonably close to optimum. We have hard water, supplied by the City of Madison. Our water has pH = 7.6, and it gets an addition of 5% white vinegar before being used on our blueberry shrubs. If you are using soft water, or rainwater, the amount of acid needed will be less, so you need to know what kind of water you have before proceeding. Also, you would have to know what kind of growing medium is in the pot. Some people grow potted blueberries in spaghnum peat moss, and this material tends to be acidic with no chemical addition needed.

I have a pH meter which tells me the pH level electronically. Most of the plants have healthy looking dark green leaves, but I feel like the more acidic the soil the more vigorous growth there will be. I have heard that using vinegar in the water would help but I have 20 bushes, and to water them all with a 2 gal watering can would take forever. My potting medium consists of 1/3 sand, 1/3 Spaghnum peat, and 1/3 organic potting soil with 3" of pine bark mulch on top.

Measuring pH in a potted plant is an issue all itself. My inclination would be to water the plant thoroughly with distilled water, and collect the leachate that runs out the hole in the bottom of the pot, and then measure the pH of the leachate. The pH meter will have to be calibrated in a solution of known pH, before testing. White vinegar, 5%, from the grocery store, has pH = 3.5, and distilled water should be very close to pH = 7. Have you measured the pH of your tap water, and if so, what is the value?

I have successfully lowered the ph from above 7 to 5.5 in my blueberry bed by applying sulfur. It took perhaps 3 years. I also fertilize with ammonium sulfate. My ph was tested at a laboratory. A Google search should direct you on how much sulfur to apply, give the type of soil in the containers.

Now if I could only get rid of the twig blight......

Marc