Tropaeolum x majus: Nasturtium
Creeping, climbing and trailing plants are generally popular but though annuals include such forms amongst their number they are by no means plentiful and besides, they are usually rather tender species. Nasturtium combines desirability of habit and hardiness, which is particularly welcomed by the working man and woman of today.
The approximately 80 species of the genus Tropaeolum are indigenous chiefly to the Andes, being found over an area extending from Central America down the entire length of South America. In their native habitat they are often perennial. Many species there are grown not only for decoration but as food. Tropaeolum tuberosum has edible tubers and the young leaves are used to make a tasty salad.
The varieties grown nowadays are the product of selection and breeding, the type species used forbeing Tropaeolum majus and T. minus, sometimes also T. peltophorum, which differs from the other two by having scarlet and being softly felted all over. Now and then one may encounter other species in cultivation, for example T. azureum, T. brachyceros, T. pentaphyllum and T. tricolor. However, the large-flowered cultivars are of greater value as decoration. Recommended are the following: ‘Scarlet Gleam’, ‘Golden Gleam’, ‘Salmon Baby’ and ‘Cherry Rose’.
Best for a window-box are the low or trailing cultivars because tall climbing forms need a strong pole or framework as a support (a wire or piece of twine such as used for beans is not enough).
Though they may be sown elsewhere and then pricked out, the large seeds are generally sown in early May directly where they are to grow, spaced 30 to 60 cm (1 to 2 ft) apart depending on the species. Flowering begins in June and the flowers are produced continuously until the frost.
If plants are provided with a free-draining, sandy loam they will flower profusely. Too much nitrogen encourages only a mass of foliage and it is then necessary to supply a phosphate fertilizer.