Petunias are excellent summer annuals for garden beds and containers. They have large, soft, trumpet-like blooms amidst soft, slightly sticky foliage. Modern forms have been developed from the species Petunia axillaris, Petunia integrifolia and Petunia violacea, which are South American in origin. The 'grandiflora' varieties (ht 40-60 cm) have large single or double blooms on strong, vigorous plants; 'multiflora' types (ht 30-40 cm) are more compact, with clusters of smaller flowers produced in greater quantity; they are also less susceptible to rain damage than the larger sorts. Semi-trailing types are suited to window boxes and hanging baskets. Petunias love sun and can tolerate dry conditions quite well once established. Petunias can be started from seed in spring, or purchased from nurseries as seedlings. Fertiliser should be added to the soil or potting mix when planting out the seedlings but it's best not to overfeed or overwater the plants once they get going, as this can give sappy growth and fewer flowers. It is helpful to pinch back the growing tips of the seedlings when they are young, to promote a bushier form. Deadhead spent blooms regularly to promote further flowering. Keep seedlings protected from slugs and snails, and watch out for caterpillars.
There is a huge range of different flower colours available these days - from traditional pastels of white, pinks and soft blue, to brilliant reds, dark blues, salmon and purples, to yellows and near-black hues! Some cultivars are bi-coloured, with throats, stripes or edges in contrasting hues, and others have very frilly edges. Because they are actually perennials in their native habitat, you cut them back when the plants become leggy in mid- to late summer, and give them a weak feed of liquid fertiliser and they will take off again and have another flush of bloom into autumn.