Petunia x hybrida
The early 18th century saw the introduction of two of the fourteen South American species of Petunia into European gardens. Both were from Argentina, almost 1 m (3 ft) high, with glandular, sticky leaves and large fragrant. The first, Petunia axillaris (syn. P. nyctaginiflora), was white, the second, P. violacea, had flowers coloured scarlet, carmine or pinkish violet. Their crossing gave rise to a vast number of hybrids of diverse size and colour. Of the many groups, three are of primary interest here, namely bedding petunias (also good for growing in earthenware urns), trailing forms for the balcony and window-box, and the ‘Grandiflora Nana’ petunias that are of small, round, bushy habit, about 25 to 30 cm (10 to 12 in) high, and simply ideal for the window-box.
Bedding petunias are taller, greatly branched and include such cultivars as: ‘Brillantrosa’ – pink, 45 cm (18 in) high; ‘Schneeball’ — white, only about 20 cm (8 in) high; ‘Senator’ — dark blue with a white mouth, also smaller; ‘Topaskonigin’ — carmine pink, almost 30 cm (1 ft) high.
Trailing forms are the loveliest for the window-box and are very attractive when combined with other annuals. Recommended are: ‘Alba’ — white; ‘Marktkonigin’ — pale carmine; ‘Purpurea’ — vivid red; and ‘Violacea’ – violet.
The ‘Grandiflora Nana’ group is the most popular. Recommended are: ‘Weisse Wolke’ — white; and ‘Karmesinrot’ — carmine red. The list could include many more lovely forms if space permitted. Extraordinarily attractive are the cultivars raised in recent years in the United States and Japan. Besides the aforesaid groups there are also others that include double and frilled forms.
Though petunias may be grown from seed sown in February, nurseries offer a wide choice of plants already in bloom so that you can be sure of getting the shape and colour you want. The window-box should be filled with a fairly heavy richsuch as John Innes potting compost No. 2 and the plants put out in May, spaced about 25 cm (10 in) apart. It is necessary to supply fertilizer during the growing season because petunias have relatively high food requirements.