Crush blackberries using a food mill and reserve juice. Strain juice off of blackberries and set aside. Measure reserved juice. Add concord grape juice to reserved blackberry juice so that it totals 3 cups of juice.
Add sugar, lemon juice and 1/2 of the box of dry jello to a pan. Bring to a rolling boil. Add certo and cook for 4 minutes.
Put in jars and cover with paraffin wax. Seal jars by properly canning. Alternatively, store in refrigerator for a week and enjoy fresh jelly.