Is this an old bush? I don't know much about chemical use, except it seems many people come here for help who have harmed their plants with too much or wrong timing.

my raspberries are Heritage. I put a little compost on top of the ground every year or two and that is it. I have never checked the PH or done a soil test and my bush is a berry making machine. I have to dig out canes each spring to keep it in check.

We have Heritage everbearing red raspberries, and our canes are up to 4-6 feet now. They are just beginning to bear ripe fruit, flowering began a few weeks ago. The patch is in heavy clay soil, that gets morning sun, and afternoon shade. I mulch the patch with shredded tree leaves in the fall, to a depth of about 6 inches. I rarely apply fertilizer, and only apply water during a drought. Raspberries grow wild on the Korean peninsula, where it gets pretty cold in the winter. They seem to thrive in our local soil and climate. Beyond that, I don't know why they grow well in our yard.