Because blackberries (Rubus fruticosus) don't continue to ripen after they're picked, harvesting them when they're juicy and not-quite-glossy is the way to enjoy them at the height of flavor. Hardy from U.S. Department of Agriculture plant hardiness zones 5 to 10, blackberries will tend to be ripe sometime around mid-summer -- though a taste test will usually help you decide.
Since they won't continue to ripen once plucked from the vine -- or keep very long -- harvest your blackberries at the peak of ripeness. Look for berries that are full, dark, and have lost some of their shiny gloss. Blackberries that are ready to harvest will come off the vine easily, though the central "plug" of the berry will stay on the vine. You can also sample the goods as you go along; if the berries taste juicy and sweet, they're ready to go.
When to Harvest
To get them at their most juicy, pick blackberries in the late morning, after the morning dew is dry. Because individual berries will be ripe at different times, spread your berry harvest out over several days or weeks.
Blackberries won't keep for long outside the refrigerator. As you pick them, place them in shallow containers with no more than three berries stacked on top of one another, and store them in a moist part of the refrigerator. Eat them within one to two days.
If you want to store them long-term, place the berries on a baking sheet and put them into the freezer, so that each berry freezes individually. Once frozen, place them in zippered storage bags and store the bags back in the freezer. Freezing them individually first prevents them from becoming a large frozen mass.