Most biennials will ripen seeds in late summer, early fall. Weather is a factor so there is no set time. When seeds are brown, dry and ready to fall from the plant and easily removed they are ready for harvest.

No they will not be ready in time to grow beets the second year. They have to be stored for planting in spring of year 3.

Missed harvested seed that fall to the ground might sprout late in year 2 but germination rate will be low and the seedlings will not survive the winter.

Dave

Thank you for the details! It's always good to know the details before jumping in. I have large gardening areas available. Combined with my recently discovered (1 yr) knowledge of planting & saving heirloom vegetable seeds equals many possibilities & future in-depth gardening adventures!

Lola