We would recommend the thornless erect varieties of Natchez, Ouachita and/or Osage. Natchez will ripen about 4-5 days before the other two varieties and is a little tarter than the other varieties in a cloudy wet season. Although these varieties do not yield as much as the thornless semi-erect blackberries like Triple Crown they ripen earlier and avoid most of the damage from Spotted wing drosophila, a new fruit fly that lays eggs in the berries beginning about the first week in July in Cadiz. You should harvest 15-20 lb of blackberries from 4 plants (1.5 lb/qt). Blackberries do not need to be cross pollinated so one variety will work. The 2015 results of our trial at Princeton Kentucky are reported on page 16 of our F&V Annual Research Report.
http://www2.ca.uky.edu/agc/pubs/PR/PR706/PR706.pdf Osage would
be expected to taste much better than is reported as the plants
were winter injured.