It says
"As most Osteospermums can only be considered half hardy, it's always best to propagate new plants by taking cuttings each year. This is preferable to over-wintering large plants.
We normally take our 5cm stem tip cuttings in autumn, although they can be rooted at any time of year given the right conditions."
I'd interpret that as meaning rather than trying to dig up and overwinter a bunch of big plants, take cuttings in fall before the things croak. That's when I take coleus cuttings, too- in fall before the suckers turn to mush.
Karen
