I like to cut back osteospermum to a neat shape over winter. Osteospermum will grow very slowly over winter so it will maintain its shape over this time. I like to shape the plant at the start of winter and I won’t need to trim it again until after its first flowering in spring. After it has flowered in spring you can deadhead the whole plant, remove all of the flowers and you will have another coverage in 2-3 weeks.