Hi, depends on which species you have, of which there are about 25, including annuals, biennials, herbaceous, semi evergreen or evergreen perennials, sub shrubs and shrubs.
You can take softwood cuttings of perennials in spring, and of sub shrubs and shrubs in early summer, but propagate them regularly as they are both short lived, annuals and biennials are grown from seed, annuals under glass in mid spring or in situ late spring, biennials in a cold frame in mid summer, Derek.