I've got 3 Jersey blueberry shrubs planted in my greenhouse, in the ground. They are 3' wide and 2' tall, producing berries nicely. They'll be bigger in the years to come but this year I planted squash in the soil between them that are very healthy. The blueberries are showing signs of nutrient deficiency (rosy colored leaves) I'd like to lower the pH (it is 7 in this bed, the rest of my beds are 6.5) just around the blueberries themselves. What would be some ways of doing this? Can I use a very diluted amount of vinegar. If I lower the pH to 6.5 just for this year will that be O.K.? What is a good compromise that satisfies both plants? What other vegetables enjoy acidic soil?
The best way to decrease the pH of your soil is to add organic matter that the acid producing microbes like, though that also takes time. To increase the acidity in soil more quickly than that it's usually recommended that you add sulfur (elemental sulfur or a sulfate) or ammonium phosphate. Vinegar will change the pH, but it is a very short-lived benefit and you have to be careful that you don't overdo it. In particular, if you have water-starved plants and you add a lot of vinegar the plants will tend to suck up more vinegar than you want.
You might try to incorporate a combination of things so that your short-term problems are addressed while still adding the sulfur that would feed for medium term and organics for the longer term. Exactly what you do would be determined by the type of sulfur you have available and also what organics you can use. Consult the fertilisers to see how long their uptake is to determine when to stop using vinegar. For organics, I usually just plan on 1 year before they start affecting my soil.
The concentration that I've seen around for vinegar is about 2 Tbsp per gallon of water when you water the plants, though you might want to go with a slightly weaker concentration initially. If you have a home tester for pH, even one that doesn't normally give you 'correct' results, it would be beneficial to test the soil just after watering with just water, then just after watering with the vinegar added the next time. You'll be looking for the change here in pH, not the absolute number, so most any tester that measures it at all would be helpful.