Prune Navajo blackberries in midsummer of their first season. Cut the main canes, or primocanes, to 36 to 48 inches at this time to encourage branch growth. Repeat this process in late summer for more growth.
Pull up any suckers between the rows. These shoots develop from the roots and suck plant energy and resources without producing fruit. Repeat this process two to three times each summer.
Prune Navajo blackberries again in early spring, before new growth shows. Cut all lateral branches back to 18 inches at this time for better fruit growth and easier harvest. Cut off any dead or diseased wood.
Prune blackberries again throughout the summer to tip the main canes for continued lateral branching. New lateral branches will produce the next season's fruit harvest. Remove the fruit-bearing lateral canes at the end of the season; these canes bear fruit once and then die.