"Rosie" wrote:

I have several CLUMPS of day lilies (probably several hundred individual
flowers now) in my new garden - when is the best time to split them up?

Then Gary answered:
Conventional wisdom is when they're dormant; practically speaking, they're
hard to kill. Dig 'em up, break 'em apart, bung 'em in the ground.

I second that, I've moved several clumps, each time generously giving some
to the neighbours. Lovely site as you drive up the road, we are all colour
co-ordinated!

Crocosmia are just the same, I'm sure I only planted 5, not the hundreds
I've now got.

Steve