Hines:

I don't know where the advice not to mulch can be coming from -- certainly not from anyone who has actually grown brambles.

Mulching is very good for brambles, and in a wide variety of climates. It will not, of course, protect the exposed canes of your Triple Crown berries from the cold. They will have to make it or not on their own. But mulching will protect the roots very well, and mulch adds nutrients, builds soil, and retains moisture in dry periods.

You would have to explain the soil conditions that led you to plant your brambles in raised beds. Perhaps you are planting over really miserable hardpan soil. It is hard to tell without some indication of where you live. But raised beds are normally not required for brambles in average soil conditions, and in cold climates expose the roots to more cold than if they were planted at grade.

I have been growing brambles in Northern Virginia for over 20 years, and started with marginal clay/shale soil. But I mulch deeply with stable manure every year, and the black soil, rich in humus, is now nearly a foot deep around the berry plants. They respond accordingly with sweet, fat berries.

Don Yellman, Great Falls, VA

What Don said. But I mildly disagree that they need the N-rich manure. I think wood chips are just perfect for brambles and for 90% of fruits. They last a long time, they make the soil a bit more acid, which they generally like, and they provide P and K and humus.

Glib:

The stable manure I use is over 70% wood chips by volume, though I always target the horse apples when loading up. Horse poop is very low in nitrogen -- not much more than 4-5%.

Of course you have to have access to a riding stable to get this stuff, and if all I could find was wood chips or sawdust, that is what I would be using. They will break down to nice black humus just like my stable manure, perhaps with a slightly different chemical mix.

I have made a career out of hauling pickup loads of this stable manure into my backyard, and usually end up with about 25 loads every yearly cycle. Some fiddle. Others burn. I haul.

Don Yellman, Great Falls, VA

I was somewhat confused on this, as well. Barbara Bowling (The Berry Grower's Companion) states in bold that she does not recommend mulching brambles after the first year due to the increased incidence of root diseases. That being said, Don's postings are persuasive (and he lives a few hours away from me), so I've started mulching mine. I'm guessing that Bowling's rule is a blanket theory that has plenty of exceptions (e.g., well drained soil, no irrigation, etc).