In the UK it is said not to pick Blackberries after October 11 (Old Michaelmas Day) because the devil has spoiled them. While the berries may become spoiled and molded, it may have more to do with the cooler, wetter weather around this time, than the devil himself, but who knows right?
Blackberries grow best from dividing up existing plants, where I live they grow wild, so there is not much need to grow them.
Blackberries’ best friends are tansy and stinging nettles, blackberry bushes also create a great environment for ladybugs (which your garden will love) and loads of other beneficial insects.
I freeze blackberries on parchment paper, and once individually frozen, they go into a freezer bag, I use them in smoothies. Wear a long sleeve shirt you don’t care about when picking, blackberries usually have thorns, and stain everything.