According to the Polish sister of Bob, she chooses long beets type to grow for canning and round beet types for eating fresh. She uses the same method for sweetness as the grandfather did.
Bob said, according to his grandfather’s method to make sweet veggies, put a tablespoon of Boric Acid around the young plant grown from seed.
I’ve heard that beets do well with extra boron. I have some Borax in the basement. I’ll give it a shot.