I've often been given advice (in blogs, books and verbally) that if you have planted a particular type of raspberry in a bed to not plant a different type. I've always been disappointed that it's not explained why this is an issue or how the problem is created, so I tried it this year and it turns out there 2 different, new, species in the raspberry bed failed. And the original is fine.
Does anyone know WHY and HOW this happens. All I currently have is proof the advice is correct, but I would like to know what occurs to make it so that new canes die in old raspberry beds?