With its multitude of coloured cultivars, this is a good small-scale salvia suited to compact spaces in the garden, usually growing no higher than 80cm. The species is native to Texas and Central America. The flowers are dainty but very profuse and the plants are in bloom for many months over summer and autumn. Salvia greggii has small leaves and is good for dry positions in the garden, being quite drought tolerant; it is also cold hardy so will cope with frosts. Like many salvias, it consorts very well with either cottage-style perennials or more semi-tropical plants. It enjoys a well-drained, sunny position (though will cope with a little shade) and can be grown in a pot. Colours include white, yellow, cerise, pinks, apricot, reds and peach. It can be pruned by about a third in May or else in stages in spring, taking off the sides at the base first and then the centre of the shrub once regrowth has occurred. It can also be pruned lightly to shape every so often during the warmer months. Severe pruning in winter, especially in cold areas, may kill the shrub. A well-known cultivar is 'Raspberry Royale' with beautiful cerise flowers which combine well with silver or plum foliage or blue flowers; it copes well with summer humidity. 'Lara' is a pretty pale pink cultivar.
In my experience, the similar species, Salvia microphylla, is probably better suited to Sydney suburbs which experience humidity in summer. There are also hybrids between Salvia microphylla and Salvia greggii, called Salvia x jamensis, which do very well in Sydney. Propagation of Salvia greggii can be tricky: cuttings seem to strike better if softwood ones are taken in spring. Layering can also be tried.