Blueberry leaves yellowing? Hydrangea blooms not returning true to colour? One possible reason for such woes might be soil pH.
Plants have different ideal conditions for growth and different ranges of comfort.
The Old Farmer's Almanac and West Virginia University lists over a hundred plants each indicating their optimal growth pH and is a probably a good place to start to see if your troubled plant likes sweet (alkaline / basic) or sour (acidic) soil.
Audrey shared as last night's meeting that she performed a simple pH test on her soil with vinegar and baking soda. About Money "Frugal Living Expert" Erin Huffstetler outlines a similar test here, step-by-step.
While this DIY is nowhere as accurate or precise as a home kit or sending samples away to a lab, it may help eliminate one possible problem and/or point you in the right direction.
Now, how to adjust soil pH? That's another story!