There’s far more to this group of plants than the familiar annuals.
2019 has been nominated ‘Year of the Nasturtium’ to promote much-loved annual Tropaeolum majus. While these easy-to-grow South American plants have sensational, jazzily coloured flowers there is much more to tropaeolum. They are incredibly diverse, with annual climbers as well as a range of tuberous perennials, equally exotically flowered, that more adventurous gardeners might want to try.
The annual species composed of T. majus and Canary creeper T. peregrinum will grow almost anywhere in full sun and are easily raised from seed, either planted directly or grown in pots under glass and planted out after the danger of frost is passed. Nasturtiums are great at quickly clothing bare soil - they will even cover ground around bamboo stems to great effect. The flowers are edible too and make mildly peppery additions to salads. They are, unfortunately, prone to infestations of blackfly, which will need to be controlled with fatty acid solutions or pinching out of the shoot tips, where most of the pests congregate. Left alone, they will soon make your prized display look very dishevelled.
The deciduous tuberous species are quite different, preferring their tubers to be in moist, but well-drained soil, but with their slender shoots able to clamber over supports into the light, where they variously flower from early to late summer. The flame creeper T. speciosum prefers cool, damp air to do well, and is a feature of many Scottish gardens in September and October. T. polyphyllum flowers in June and looks good when allowed to grow over a scree in a rock garden. T. tuberosum needs a warm spot, where its long-spurred flowers appear from August. Try enchanting T. tricolour in a deep pot of gritty loam-based in a cold greenhouse, where its multicoloured flowers will attract gasps of admiration before it dies down and becomes dormant in summer, before starting again in autumn.