How to select for best flavor:
Ripe blackberries are completely black and plump. Avoid berries that are red or green or show signs of mold. Usually blackberries are sold in pint or quart boxes. As with other berries, avoid boxes that are stained with juice. This is a sign of over maturity or decay.
blackberries grow wild in many parts of the country and you can gather them yourself. Choose berries that are plump and completely black. When they are perfectly ripe, they will fall off the vine into your hand with only a small tug.
Peak of the season:
Blackberries are in season from June through August. The most and the best are available in August. Picking your own, especially if you live in the northwest, is the cheapest source of the best berries.
Blackberries are a pretty good source of calcium, potassium and vitamins A and C. One cup of raw berries provides about 75 calories, 1 gram of fat and almost no sodium or cholesterol. Blackberries contain an as yet unidentified substance that aids in digestion and stops diarrhea. They also are a good source of fiber.
Blackberry cultivation is a fairly new phenomenon, since blackberries grow wild nearly everywhere in North America. In fact, in many places they are a tenacious weed that is nearly impossible to get rid of or to contain.
Because of the medicinal properties of blackberries, cease fires were sometimes called during the Civil War so that soldiers suffering from dystentery could forage for about blackberries near the battlefield. The leaves and stems of the blackberry have often been used to make a medicinal tea.