Common name: Nasturtium

Nasturtium is a flowering herb native to the highlands of South America, with its natural range extending along the Andes Mountains from Colombia to Bolivia.

The stems are soft and succulent, and they grow quickly with a trailing habit, branching and spreading along the ground, cascading over walls, and climbing structures such as fences to heights of up to 2 m (6.6 ft). In warm climates, without frost or extreme heat and with adequate moisture, it is a self-propagating perennial that puts down roots and re-seeds as it grows.

Leaves are medium-green, disc-shaped with wavy margins and from 5 to 15 cm (2 to 6 in) in diameter. They are held above the ground on long, erect leaf stalks and grow close together, with the edges overlapping and shading the ground beneath them.

Nasturtium blooms throughout the year, producing solitary, trumpet-shaped flowers on erect stalks in shades of yellow, orange or red, contrasting strongly with the green of the leaves. Fertilised flowers develop into roundish, green, pea-sized fruit divided into three spongy segments, each enclosing a single seed. 

In the tropics, the leaves and flowers are most abundant during the year's cooler months.

Melbourne, Australia

Environmental uses

Groundcover - Nasturtium is a widely cultivated herb in gardens for its ability to cover ground quickly, suppress weeds and conserve soil moisture.

Poolside plant - It is also well-suited to poolside landscapes, containers, and raised garden beds because of its trailing, cascading habit.

Foliage ornamental - Its attractive foliage is a bonus.

Flowering ornamental - ...as are its brightly coloured flowers.

Hummingbird attractant - The flowers also attract hummingbirds...

Butterfly attractant - ...butterflies...

Bee forage - ...bees, and other beneficial insects, providing forage that also makes the plant suitable for companion planting, especially in vegetable beds.

Edible uses

Salad vegetable - The young leaves and flowers are edible and have a sharp, peppery taste like watercress because of mustard oil. They are used as a garnish or added to salads for their flavour, colour and visual interest. The older leaves are generally not used because they are intensely flavoured and somewhat bitter.

Pickled vegetable - The unopened flower buds are pickled whole, usually in a flavoured brine. They are comparable to capers in how they are prepared and eaten.

Climate

Grows naturally in humid, cool subtropical and tropical mid- to high-elevation climates, generally frost-free areas with annual lows of 7 to 18°C, annual highs of 15 to 27°C, annual rainfall of 700 to 3500 mm and a dry season of 5 months or less.

Nasturtium can also be cultivated with irrigation in much drier and warmer climates, though with markedly less success because the plant cannot cope with excessively hot, dry conditions.

Growing

New plants can be started from seed or cuttings. They perform best in moderately fertile, free-draining loam and sand soils that are slightly acidic to slightly alkaline, generally with a pH of 6.0 to 7.5. Rich soils with high nitrogen levels encourage leaf growth, often at the expense of flowering. 

Over-exposure to the hot afternoon sun can cause it to die back and become unsightly. For this reason, it is best grown in tropical lowland areas as an annual during the cool months of the year, with shade from the afternoon sun. In cool, high-elevation tropical areas, it grows well in full sun year-round.

Problem features

The fruits are buoyant and easily dispersed by moving water, which can carry them and their seed afar. It is listed as a serious weed in at least one reference publication and is assessed as a high weed risk species for Hawaii by the Hawaii Pacific Weed Risk Assessment (HPWRA) project.

Books

• Adams, C. D. 1972, Flowering plants of Jamaica, University of the West Indies, Mona, Greater Kingston

• Editors of Sunset Magazine 2012, The New Western Garden Book: The Ultimate Gardening Guide, 9th edition, Sunset Publishing Corporation, California

• Griffiths, M. & Burras, J. K. 1994, Manual of climbers and wall plants, Royal Horticultural Society (Great Britain), Timber Press, Portland, Oregon

• Iremonger, S. 2002, A guide to plants in the Blue Mountains of Jamaica, University of the West Indies Press, Kingston, Jamaica

• Jamieson, G. S. 1943, Vegetable fats and oils : their chemistry, production, and utilization for edible, medicinal and technical purposes, 2d ed, Reinhold, New York

• Jex-Blake, A. J. 1957, Gardening in East Africa : a practical handbook, 4th ed., Royal Kenya Horticultural Society, Longmans, Green and Company, London

• Macmillan, H. F. 1943, Tropical planting and gardening : with special reference to Ceylon, 5th ed, Macmillan Publishing, London

• Martin, F. W & Ruberte, R. M. 1975, Edible leaves of the tropics, U.S. Agency for International Development (USAID), and the Agricultural Research Service, U.S. Department of Agriculture (USDA), Mayaguez, Puerto Rico

• Randall, R. P. 2007, The introduced flora of Australia and its weed status, Cooperative Research Centre for Australian Weed Management, Glen Osmond, South Australia

• Rubatzky, V. E. & Yamaguchi, M. 1997, World vegetables : principles, production, and nutritive values, 2nd ed., Chapman & Hall, New York

• Weiss, E. A 2002, Spice crops, CABI Publishing, Wallingford, United Kingdom

• Woodward, Penny 1997, Pest-repellent plants, Hyland House, South Melbourne