I've divided rhubarb (successfully) most any time of year although my preference is Fall when it is shutting down for winter. I just take my shovel, dig straight down into an edge of the crown and cut off a chunk. Then I fill in the void with compost and leaf mulch. I plant the chunk with compost too.

Honestly I have tried to kill this crown once. I dug it up, broke it into pieces, gave away as much as I could and tried to compost the leftover pieces for 2 years. But even the smallest chunks kept leafing out in the pile every spring. Haha. So I gave up, put it back in the garden and we're both very happy now.

Kris

Hey, Kris....thanks for the information on the rhubarb. I went out and dug down and took off a corner of the plant, and planted four chunks; just like I knew what I was doing.
Anyway, the wife is very impressed with my rhubarb knowledge. I didn't bother telling her that you're the smart one, and an hour ago, I had no idea of what I was going to do.
Really surprised on how large the plant was. Next year, if it lives, I'll divide it again....Can't get enough rhubarb.
Thanks again for the help,
jim Peterson
Gardnerville Nevada/Bacubirito Mexico

Good luck, Jim. And you are right...Since I've totally reformed I know you just can't have enough rhubarb! ;-D YUM! In fact I gave away a football sized clump just a couple of weeks ago. (I've become the local enabler for 'sour' heads...hehe)
Kris
P.S. Here's a pic of my plant earlier this spring...