Osmacote will add slight acidity, but I believe you can purchase Sulphur for the purpose. There are also fertilizers made specifically for blueberries that will do it, too. Just ask your local garden center for some, all the ones in my neck of the woods carry a few brands.

Here in Madison, Wisconsin, I mix in one pound of agricultural sulfur with the soil in the hole, when planting a blueberry shrub. After the shrub is planted, I spread one more pound of sulfur around the shrub, in a three foot diameter circle. Then I put down about 6 inches of mulch, usually shredded maple tree leaves, which covers up the sulfur. We have soil with high pH, around 7.6. Your soil might be different. Do you have hard water?

You can use coffee grounds, but you would need Starbucks type quantities to lower the pH rapidly enough to make a big difference with typical Michigan soils (but, it depends a lot -- some areas have acidic soils naturally).

You would be better off using Aluminum sulphate or sulfur from the garden center.

Shadbush/Juneberry/Saskatoon is a great and underutilized fruit. I love mine. But, not everyone likes it -- some people object to the seeds.

how long should blueberries remain blue on the plants before harvesting??

charleslou23, it is ok to ask questions on other peoples threads but please refrain from hijacking every thread with the same question. Give people a chance to answer your question.

Dale