How do I grow black eyed Susan's?

Either way will work. Just do not transplant in the heat of the day. Early morning or early evening after the sun is not in the location where you want to plant them.

you can do either rooted plants need done in Fall before ground freeze; seeds can either be thrown out in Fall as they would naturally fall from seed heads or you can start them in late Spring(after Mothers Day is best) you don't say where you live so this is just general info. the main difference in transplanting part of plant and planting seeds is maturity of plant the seeds may not bloom much til following year/season even could take 2 yrs/seasons when they are more established. you need to wait til plants have died back naturally then transplant do not remove tops completely the plants need the tops for nourishment and you'll be able to see where you have planted them easier,only remove dead tops in Spring after you see new growth starting