yes, a soil test is a good measure, but there are some nutritional requirements of blueberies and cherries that you can be aware of. Assuming...
You can buy a soil test kit from a gardening store. You can buy kits to measure nutrient contents as well as pH. I would highly recommend doing...
I would recommend amending your soil, lots of tilling, its easier than dumping more soil on top. Make sure you add a good quality fertilizer to...
I use Bug Away, made by advanced nutrients. Effective, guaranteed, and most importantly!! Organic.
Do you water the cacti really intensely and then let them dry out? If so, it could be salinization .. which would be aggrivated by excess...