Just mulch heavily, please don't use herbicides. Mulch, mulch, mulch! Blackberries are pretty hardy, they will likely emerge.. Also, just keep pulling the weeds roots.. Pull and mulch, pull and mulch!

Weeds aren't going to damage your canes, why spray poisons on them just for your own preference? Work with the weeds! Research foraging, find out what weeds is growing, it is probably edible, and highly medicinal. A lot of weeds grow for a reason, to benefit the soil, not to hurt anything. Lay down a layer of mulch and watch your problem dissipate.

Joe

Joe,

Thanks for the info. I'll get the kids to pulling weeds and mulch them.

Karl

Keeping a one-foot radius free of weeds around each blackberry clump is all that's necessary. Mulch that area 3-4" to suppress weeds; primocanes will emerge fine.

Clearing a larger radius of weeds will allow weeding less often as they will not encroach on the canes so often.

Add some sand to the surface. When you weed, the sand works itself in and makes weeding easier the next time. The blackberries like the sand too.

Spread newspapers or cardboard under the mulch to help suppress weeds even more. Northwoodswis

Landscape fabric if used by alot of commercial growers, there is a poster on this site that has a u-pick farm, see his pictures of how he does it.

Here is a link that might be useful: Barber berry farm

I've done everything that is suggested above and I still have lots and lots of weeds. If you apply a lot of mulch, it eventually breaks down into compost and makes a nice fluffy layer on the surface. Weeds are a lot easier to pull out of the fluff than the soil.

Yeah, what John said, all these weed seeds that grow up in my mulch come out very easily...

Thank all of you for the information.