A deep mulch around highbush blueberry plants increases growth and yield, according to Virginia Extension specialist Charlie O’Dell. Writing in the American/Western Fruit Grower in December, O’Dell describes trials in which he mulched blueberries with 6 inches to 12 inches of sawdust. He cautions against using black walnut sawdust, because of its allelopathic effects on other plants. He did not notice any greater damage from voles and mice in the heavily mulched plants. The mulched plants require about twice the nitrogen of unmulched plants.
O’Dell recommends that newly transplanted blueberries get 2 inches of mulch the first year. Deeper mulch can be applied in subsequent years.