I leave most of my perennials standing through the winter, and cut down in Spring, but for the most part that is a personal choice as to how you prefer to tend your gardens. If you cut your Asters down after blooming you won't get seed. If you want to divide and transplant, the Spring would probably be better, as these are fall bloomers.

New England aster is supposed to reseed but mine never have that I've noticed (others types of Asters self-sow abundantly though). I have started these from seed successfully using the winter-sowing method, and got one of the rarer pink colored plants. Then I collected seed and winter-sowed those, to see if I can get the pink color to come true from seed (they didn't flower this year though).

I have grown a lot of asters both NE and NY, I find with the New England asters it is better to wait until spring to divide. The New Yorks are not so fussy. I cut some of the taller asters back a bit but leave most of the cleanup for the following spring. I have never collected seed so no help there but would imagine winter sowing would work well.

Annette

According to Bill Cullina, you need more than one aster plant (of the same type) to get viable seeds. If you have only one, you may not get any self-sown plants. I get lots of New England seedlings from Alma Potschke, Purple Dome, Hella Lacey etc. They most likely do not seed true to type. Purple Dome, for example, is a natural dwarf, but I get purple seedlings that are very tall, so maybe they have reverted (??) to the natural height in the wild. Collect the seeds in late fall when the "parachutes have begun to dry and expand". Store dry in the fridge until seed can be sown. Seed can be sown outdoors in the fall with germination the following spring, or it can be sown in the early spring.