@Tinpot, what variety of rudbeckia are they? Some varieties in my experience are difficult to divide, they do not form rosettes/ plantlets that can be eased apart. I find greater success taking basal cuttings instead, taken when the plant is in active growth and new shoots from the base are 2 inches long. All 4 cuttings I took last spring flowered well last year. I used them in containers and potted them up in November into 2L pots. These are now overwintered in my standing plastic greenhouse and will go into the borders in late spring.