Plant of the week: Nasturtiums
There’s far more to this group of plants than the familiar annuals
It’s the Year of the Nasturtium in 2019 to promote much-loved annual Tropaeolum majus. While these easy-to-grow South American plants have jazzily coloured flowers, there’s much more to tropaeolum. They’re incredibly diverse, with annual climbers as well as a range of tuberous perennials.
The annual species composed of T. majus and canary creeper T. peregrinum 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 has passed.
Nasturtiums are great at quickly clothing bare soil. Flowers are edible and a peppery addition to salads. They’re, unfortunately, prone to infestations of blackfly, which need controlling with fatty acid solutions or pinching out the shoot tips, where most of the pests congregate.
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 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 compost 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.