Answer: I doubt the problem is with the pine bark, but I know that a good dose of fertilizer in the spring will aid growth and increase production. Also, if you suffered with the same drought conditions we did last summer, I'm not surprised the plants didn't produce as much as usual. Brambles have shallow root systems, and need regular irrigation if rain isn't sufficient. Sometimes, too, viruses spread from wild plants by insects infect the plants, and render them pretty useless. In that case, it's best to replace them entirely. Infected plants show stunted or deformed growth, and an off-color foliage.
To maintain soil nutrients for your raspberry patch, each spring before the canes show signs of growth, rake back the mulch and apply about a half-pound of well-rotted cow manure. Rake the mulch back into place. You may need to spread more fresh mulch at the same time, since you mention that it has broken down quite a bit over the years. I hope this helps get your brambles back in shape!
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