Three years ago when I was establishing my garden I planted two berry producing plants, and one of those was the Prime Jim variety of blackberries. Developed at the University of Arkansas, Prime Jim is one of three primocane varieties commercially available.
All but three varieties of blackberries are floricanes, meaning that they flower and fruit once a year on the second year canes. In other words the canes grow for one year without producing flowers or fruit, and then the second year they do.
Primocanes produce flowing and fruit on both first year and second year canes. Second year canes flower in the spring and fruit during the summer. First year canes flower in the summer and fruit in the fall. So at this time, when I’m harvesting berries from last year’s canes, I’m beginning to see flowers on this year’s new growth.
If you really like blackberries and have space to grow them, here’s a few tips to maximize their growth and production. First, they are better grown on a slope because their bed must drain off any excess water. If you’re dealing with a heavy clay soil then you should consider adding sand and leaf mulch to build up the bed while making sure that it drains.
Second, any plant that produces fruit will require higher amounts of phosphorus and potassium than green plants that use more nitrogen. Because phosphorus is relatively stable and doesn’t leach out, it’s important that you mix phosphorus into the bed and throughout the root zone. My preference is super phosphate which is simply rock phosphate treated with phosphoric acid, but you can use rock phosphate or bone meal to supplement the bed, you’ll just have to use more of it.
Blackberries like acid soils and mulching with leaves maintains the acidity. I flag the second year canes and prune them out in the fall because they die back anyway, and end up clogging the patch. This is a good practice even if you’re growing a floricane variety.
You can get additional information on all varieties of blackberries produced by the University of Arkansas here. They also have links to vendors where you can purchase their varieties. Personally I really like having a patch of blackberries close to home, and you might enjoy that too.