Knowledgebase
Soil prep for blueberries #749945
Asked May 14, 2021, 2:26 PM EDT
Ramsey County Minnesota
Expert Response
You don't mention the pH or other characteristics of the native soil so we presume the test results pertain solely to the soil mix you described.
Because it can take several months for the pH of such a mix to be fully expressed, some change from the original test results would be expected. How much depends upon the nature of the materials used to create the mix.
Characteristics of the "black dirt" might account for the pH increase from the original test. The following information may be relevant in that regard.
https://www.canr.msu.edu/news/the_shocking_truth_about_topsoil
It isn't always feasible to lower soil pH with elemental sulfur and the test results indicate that's so in your case. The following publication explains why. (See paragraph 2.) Other information in this publication may also be helpful
https://hort.extension.wisc.edu/articles/reducing-soil-ph
If you are unable to make the native soil or the mix you described suitable for growing blueberries, consider growing them in raised beds. For raised beds mix equal volumes peat moss with acid compost or planting mix.