Prime-Ark 45 is a primocane-fruiting blackberry, which is a fancy way of saying it fruits on both new and older canes. Second-year canes carry the heaviest crop starting in early summer, then this year's new canes pick up the slack as summer rolls on, often carrying berries into fall.
The fruit is dark purple-black, medium-sized, and unusually firm, with excellent shelf life so berries hold up in the fridge instead of turning to mush overnight. Canes reach 4 to 8 ft. tall and 3 to 6 ft. wide, and respond well to pruning if you want to keep them tidy along a fence, trellis, or the back of a raised bed.
Plant one this season and you'll be picking blackberries by the handful from early summer well into fall.