South African Nemesia (ht 30 cm) are soft, dainty plants often sold in small pots for 'instant colour'. They are certainly useful for filling gaps, but they are good plants in their own right for a mixed border where a carpet of long-lasting colour is wanted. The dainty flowers look like little orchids, and come in hues of pinks, purple, blue, cerise and white, with bi-coloured versions as well. Some popular cultivars include 'Blueberry Ripple' (deep purple) and 'Strawberry Ripple' (mid-pink). Over time, they spread to form a clump, and in my experience, they will flower for several years. Though sold as an annual, some species are actually tender perennials, and will survive at least a couple of years in Sydney gardens if trimmed back regularly and fed occasionally. The most commonly seen of these seems to be Nemesia coerulea (sometimes known as Nemesia caerulea). It may self-seed, perpetuating itself from year to year this way. Nemesia strumosa is a true annual, which can be grown from seed, and it has a range of colours, including reds and oranges as well as pastel hues.
The plants like a moisture-retentive soil that has organic matter added in, but it also needs to be well-drained. They like sun but appreciate protection from the hot afternoon sun in summer. They will flower from spring till autumn unless the summer is very hot. Pinch out the growing tips of young plants to encourage bushiness. Cut them back periodically when blooming flags, to give them a new lease on life. They provide a haze of colour between plants of more structural form; they are also well suited to growing in containers. They may self-seed where they are happy.