I just divided my asters (white, panicled, and late-blue) with just either a knife(if they were small) or a shovel(just push through the roots and dig up the piece you want). That may seem a bit harsh, but asters are sturdy plants that never need to be babied. The roots heal quickly and resume growing soon. I've never had a problem with dividing them. Just keep both parts watered at least once a day for 4 or 5 days.
I hope you have good results.

The power of the prairie is those wonderful root systems, that are a pain to divide. I have found that using a hand saw to slice the removed root clump into sections is much easier than trying to pry it apart with a shovel.

I don't think you have to worry about being too destructive. The plants are hearty. I frequently clip back spring growth in June to keep the plants from becoming too tall in the fall.

I use a shovel. I plaec it where I want to cut and stand or jump on the shovel to drive it through the roots. This doesn't turn out to be nearly as destructive as it sounds. I usually get a clean cut, and after several cuts I can remove a section and tranplant it. I would dig up the whole thing, as this would disturb all of the roots and be a significant setback to the original plant.

Thanks, everyone. I think joepyeweed has the best sense of just what the root of this baby is like. Shovels, even sharpened, even with my 170 lbs pounding on them, just bounce off with a sort of POING!!! effect. I've been trying to avoid the saw routine, but that may be it. I'll try again this week-end and report back.

I used to have an old hand saw I used for this purpose. Now I get as much dirt off the rootball as possible and use a sawzall with a 12" pruning blade. You can't kill 'em.

Yup, it took a saw. Dug the root up, and it had a solid core about 18 inches across and dense. Took a while to whack it into quarters with the rusty old pruning saw I chose for the work, but it eventually cut through. I can see why using a sawzall (if I had one) would be appealing. Thanks everyone for you suggestions.

I've never been able to divide the stuff with a shovel... jumping on the shovel, just bounces right back. I like the sawszall idea, though.

I had to do the same thing for clumps of big bluestem and indian grass.

I am actually pondering taking on a big clump of little bluestem this coming week-end and was hoping the spade would do it, as it did once before. But we may be past that stage and into saw territory now.

I have been able to use shovel on some plants, I think it depends upon the age of the plant and the soil its growing in.

I always try the shovel first and if it doesn't work, then I get out the saw...