Thinning Walnut Thinning : Thinning reduces the stand so that growth is distributed to those trees you wish to keep for future products. Thinning should leave 25 to 30 trees per acre for nut production, and 75 to 100 trees per acre for lumber production. A thinning may be required two or more times during the life of the stand.Avoid thinning before trees reach a size at which they can...