Osteospermum is getting too big!

Hi, if it's really woody, I don't think you could split it, prune it back in Spring, this is what I did with my Spanish ones, I used to prune mine really hard then they would send out new leaves from the centre, only other thing, dig it out, replenish the soil and buy a smaller new one, they're not very expensive. You can see mine on my pics.

Peg a few pieces from the large plant down, when they have rooted(as they will in a very short time)then take out the old plant.