Mix the fruit and sugar. Place the blackberries and full amount of sugar into the saucepan and mix well. Let it sit at room temperature for about 20 minutes while you prepare for canning
Prep your equipment. Fill the canner ¾ full of tap water and start to heat on the stovetop. Place the rings and lids in a small saucepan of water and bring to a simmer. Heat the clean mason jars in hot water in the canner, the dishwasher, or the oven set to 200℉.
Mash the fruit and add the remaining ingredients. Using a potato masher, mash the fruit until no whole blackberries remain. Add the pectin and lemon juice and mix well.
Boil the jam and skim the foam. Bring the mixture to a full rolling boil that can't be stirred down. Once you've reached this, let the jam boil for five minutes, stirring constantly so it doesn't scorch. Once set, remove any foam with a spoon or offset spatula.
Put jam in jars. Using a canning funnel, pour the finished jam into your hot, clean mason jars. Run a clean, hot butter knife around the inside to remove any air bubbles. Wipe the rims clean. Place the lids and rings on top and twist them fingertip tight.
Process in canner. Using the rack, lower the jars into a canner that is at a full rolling boil. Once it has returned to a boil, start the timer. Half pints need 10 minutes and full pint jars need 15 minutes. When the time is up, carefully lift the rack and remove the jars using a jar remover. Place on a clean dish towel on the counter. The jars will seal within 24 hours.