Nemesia strumosa hybrids are usually grown as half-hardy annuals, though they might make short-lived perennials in very mild climates. We grow them as winter annuals here in the subtropical desert. However, there are many half-hardy perennial species, such as N. fruticans, and N. caerulea. There has been quite a lot of hybridizing involving perennial species lately, and the results haven't made it into many gardening books, yet.