Bob and I picked about 1.5 gallons the other day and I am going out again tomorrow.
The trouble with wild blackberries is that since we don't plant, water, fertilize or do anything at all to them, we do have to pay our due somehow. And, with blackberries, they extract a pound of flesh. This is not a metaphor, they do extract a pound [or less] of flesh.
The are picky beyond imagining and they actually grab at you and pull your hair, scratch your arms and other parts of your body even if they are covered with clothes.
But, it is a small price to pay for blackberry pie, blackberry jam, blackberry muffins, blackberries on your Cheerios and fresh blackberries that stain your hands and teeth and burst forth amazing flavor.
We have some cultivated, thornless blackberries too, but they ripen a bit later.
Combine in a 4 quart sauce pan:
2 cups mashed blackberries
2 Cups white sugar
2 tsp lemon juice
Heat over med-high heat till boiling and boil hard for 5 minutes, stirring occasionally. Turn heat down and simmer for 15 minutes. Put in jars and enjoy. If you want to can it, just put in hot sterile jars [you can wash them in the dishwasher and then keep them warm by filling with hot water while you wait for jam to finish boiling]. Heat canning lids in hot water for 10 minutes while jam is boiling, no need to boil water, but you should have them on the stove, in a pan in very hot, nearly boiling water.