Blackberries need soil water traveling downward all time even if slow crown needs to be in dry soil is ideal. Yes I would mound any soil that I planted berries in sand good black sand better black comes as organic matter in soil.

Our soil type, here in Madison, Wisconsin, is very different from yours. So I am not sure if this will help, but here goes. Raspberries do well in full sun, in soil that will retain some moisture, so they never dry out. It happens that our soil is high in clay content, and clay retains moisture well, so all I have to do is keep adding shredded tree leaves, every fall, to raise the level of organic matter in the soil. Despite the clay, our soil does drain eventually, and I am not seeing evidence of root rot on any of our plants, raspberries included. I have not found it necessary to mound the soil. I would consider this if I was trying to grow raspberries in a low spot that ponded after a rainfall.

ericwi: The last place I lived I planted my raspberries in a clayey soil and while the blackberries thrived near them, the raspberries never grew. I did not mound my soil then. I'm amazed that your raspberries are all good, the organic matter you regularly add no doubt helps.

Thanks for the advice and experiences.

My raspberries grow at the bottom of my steeply E/W sloping allotment in heavy clay soil which never dries out, but does not flood. They grow on woodland edges in the wild and full sun all day is not imperative. Mine get very little sun in winter and only from about 9 am in high Summer (when there IS any sun!).They are shaded by tall buildings to the East. They get a leaf mulch every autumn and the odd dollop of manure but apart from that they appear to get all they need from the soil. A main consideration in my view when planting raspberries is to ensure you have got absolutely every morsel of perennial weeds out of the ground before you plant. They are going to be in situ for a good few years and bindweed, couch or other intransigent weeds can be a nightmare.

Can't help with blackberries - I don't have the space for them and wild ones are all around.

I wouldn't mound soil for blackberries, especially if you have somewhat sandy sloping soil that readily dries out in June through August. And your sandy mounds might get eroded in heavy rain or irrigation. Better to have a raised area for the whole row rather than just mounds. Slightly trench the space in between rows and put that dirt on the rows.