Nasturtium (Tropaeolum majus): complete guide to growing and uses

Daniel Platteau Annuals & biennials Vegetable garden plants

Biology and botanical characteristics

The nasturtium belongs to the genus Tropaeolum, family Tropaeolaceae, order Brassicales. Its most common scientific name is Tropaeolum majus L., described by Carl Linnaeus in 1753. It is a herbaceous annual, or a short-lived perennial in mild climates, native to the Andes of South America (Peru, Ecuador, Bolivia).

Climbing or bushy depending on the variety, it produces succulent stems that can reach 1 to 3 metres long. The leaves are alternate, entire, round and peltate (the leaf stalk joins the centre of the blade), 3 to 8 cm across, shaped like a shield. This feature inspired its genus name, from the Greek tropaion (trophy): Linnaeus saw shields in the leaves and helmets in the flowers, like those hung on ancient military trophies.

The flowers are solitary, in the leaf axils. They are zygomorphic, with five sepals, the upper one extended into a long nectar spur 2 to 4 cm long, and five petals that are usually orange, yellow or bright red, sometimes blotched or streaked. There are eight free stamens. When ripe, the fruit splits into three mericarps, each containing one large, wrinkled seed that germinates easily.

History and discovery

The nasturtium is a neotropical plant known to Andean peoples long before Europeans arrived. Its cousin Tropaeolum tuberosum (mashua) is still grown there for its tubers.

The dwarf nasturtium (Tropaeolum minus) reached Europe as early as the 16th century. The garden nasturtium (Tropaeolum majus) was only introduced at the end of the 17th century, around 1684, via the Netherlands, before spreading through European gardens in the 18th century. Linnaeus gave its definitive description in 1753 in Species Plantarum.

Its French name, "capucine", comes from the shape of the flower and its spur, which recall the hood (capuce) of Capuchin friars. In English it is called "nasturtium" (from the Latin nasus tortus, "twisted nose"), a name borrowed from watercress, because its leaves have the same pungent taste that makes you wrinkle your nose.

Growing and care in the garden

Growing conditions

The nasturtium is a full-sun plant that tolerates light partial shade well, especially in regions with scorching summers. It prefers light, well-drained soils that are poor to moderately rich. Soil that is too fertile, particularly rich in nitrogen, produces lush foliage at the expense of flowers. The ideal pH is between 6.0 and 7.5.

It does not tolerate frost: the first autumn frosts kill it. Its seeds germinate once the soil is above 10 to 12 °C. In mild climates (by the sea, Mediterranean climate), it self-seeds readily and can behave like a short-lived perennial.

Sowing and planting

Direct sowing: from April to June, 2 or 3 seeds per station, 20 to 30 cm apart, 1 to 2 cm deep.
Sowing in pots: under unheated cover in March–April, planting out after the last frosts.
Seeds germinate in 10 to 20 days at 15–18 °C; soaking for 12 hours in lukewarm water speeds things up.
Cuttings: softwood stem cuttings root easily in water or in moist compost in spring.

For climbing varieties, provide a trellis, a light fence or wire mesh, which it grips by twisting its leaf stalks. Dwarf varieties form mounds 30 to 40 cm high, perfect for edging, window boxes and hanging baskets. Water moderately: the nasturtium copes better with a short dry spell than with too much water, which rots the roots.

Note: overwatering and poorly drained soils are the main causes of nasturtiums failing. Use a light growing medium and water at the base.

Flowers, leaves, seeds: a plant with many uses

The nasturtium is both ornamental and edible. All its above-ground parts are edible and have a characteristic peppery flavour, due to glucotropaeolin, a sulphur compound (glucosinolate) similar to those in watercress and mustard.

Culinary uses

Fresh flowers: to decorate salads, pasta, tarts or cold soups; slightly peppery and sweet.
Young leaves: in salads or pesto, for their refreshing bite.
Flower buds and green seeds: pickled in vinegar, they make an excellent substitute for capers ("poor man's capers").
Infusions: the flowers and leaves go into some herbal teas.

Properties and traditional uses

Rich in vitamin C, it was historically used against scurvy.
It is traditionally credited with antibacterial and expectorant properties, particularly for the airways; these uses do not replace medical advice.
The fresh leaves are sometimes applied as a compress on minor skin irritations.
Companion plant in the vegetable garden: it attracts aphids and cabbage white butterflies, and can thus divert some of these pests from nearby cabbages. Use it as a trap crop with care: badly placed, it also becomes an aphid reservoir.

Diseases, pests and common problems

Although vigorous, the nasturtium is not free of enemies. It remains easy to grow but needs a little watching.

Pests

Caterpillars of the cabbage white butterflies (Pieris brassicae and P. rapae): like cabbages, the nasturtium belongs to the Brassicales and attracts these butterflies; a heavy infestation can strip the plants.
Blackfly (black bean aphid): it colonises stems and flower buds, especially in early summer.
Slugs and snails: particularly active on young plants in spring.
Mealybugs and whitefly: rare outdoors, more common under cover.

Diseases and disorders

Grey mould (Botrytis cinerea) and root rot (Pythium, Rhizoctonia): linked to excess water, poor air circulation and heavy soils. Pay attention to drainage.
Powdery mildew: white powder on the foliage at the end of the season; remove affected leaves and space plants out.
Yellowing foliage: often due to waterlogged soil or, more rarely, a deficiency.

Varieties and where to find them

The horticultural market offers a wide range of varieties selected for their habit, colour or foliage. Seeds are easy to find and plants are sold in spring in every garden centre.

Main varieties

'Alaska': a dwarf variety with cream-and-green variegated foliage and multicoloured flowers (red, orange, yellow). 30 cm tall. Ideal for window boxes and edging.
'Empress of India': an old variety with deep red flowers and dark blue-green foliage. Bushy habit, 30 to 40 cm.
'Whirlybird': a series of upward-facing, spurless semi-double flowers in various colours. Does well in pots.
'Peach Melba': pale yellow flowers blotched orange-red at the centre, very decorative, dwarf habit.
'Jewel': dwarf nasturtiums of 25 to 30 cm, early and dense flowering, wide colour range.
'Gleam': a semi-trailing series with semi-double flowers, lovely in hanging baskets or as ground cover.
Climbing nasturtiums ('Tall Single Mixed' and other "tall nasturtiums"): they can exceed 2 m, perfect for hiding a fence.

Seed packets are available from seed companies (Vilmorin, Ferme de Sainte-Marthe, Kokopelli, Baumaux…) and in DIY and garden superstores. Plug plants are available from May to June. For heritage varieties, turn to specialist organic seed producers or seed swaps between gardeners.

The nasturtium is the ideal plant for beginners: easy sowing, quick germination, generous flowering and great resilience, as long as you give it sun and well-drained soil.