Below is a list of harvest dates from blackberry trials that we have conducted in North Carolina since 2008. The trials were at three locations in NC, the Piedmont Research Station in Salisbury, the Mountain Horticultural Crops Research and Extension Center in Mills River and at the Upper Mountain Research Station in Laurel Springs. The trials were replicated with plots both under high tunnels and grown outside at all three locations. First harvest is approximately the date when 5% of the fruit from the entire season was harvested, peak harvest is when 50% of the total crop was harvested and 95% represents the last harvest date. There are 7 different blackberries represented, most were at all of the trial locations. Harvest dates do vary from year to year and with location. For example, the earliest and latest harvest dates for Navaho was 18 June 2010 in Salisbury, and 31 July 2010 in Laurel Springs respectively. We don't have a model for NC, but I thought this may help you with determining dates for your farm.