Black plastic is one of the best mulch choices when growing blackberries, according to SFGate. Blackberries need a lot of moisture to produce high yields of fruit, so using mulch to conserve soil moisture is important. If using black plastic for mulch, an efficient drip-irrigation system is required.
Pine needles and shredded pine bark are also excellent choices for mulching blackberries. Pine needles should be layered 4 inches thick. They can also be layered on top of black plastic to protect the plastic from breaking down chemically in the sunlight. Wheat straw can also be used as a mulch for blackberries, but it is flammable and can leach nitrogen from the soil.