Natalie,
I halved and moved those big ones in June - not long before some of them bloomed, and in very, very hot and dry conditions. So, yes, they were in full growth. These were massive clumps tho' - I had to drag 'em over to the new spot riding on the shovel. No way could I actually lift them!
When I split hostas for moving I don't worry much about digging big
around - for me they do great if I get a
deep and slender, plug of ground. 'Course we have that heavy clay and I'd bet that helps.
I'd say, go for it - just water them in really good.
