Nasturtium: profile, hardiness & propagation
The bright and colourful nasturtium flowers not only look magnificent in the garden but also on the plate. Did you know that you can eat these flowers?
Nasturtium (Tropaeolum) is usually cultivated as an annual flower because of its sensitivity to the cold. Thanks to its pharmacological effect, nasturtium was named medicinal plant of the year in 2013. Read on to discover the properties of this unique plant, including whether nasturtium is hardy and how to propagate it.
Nasturtium: origin and profile
When referring to the “nasturtium” plant, also known as Indian cress, some confusion may arise because it is not related to the similar watercress plant that belongs to the Nasturtium genus. Despite being unrelated, these two cresses actually have a similar taste. The nasturtium plants form a family of their own in the plant kingdom, known as the Tropaeolaceae. The garden nasturtium (Tropaeolum majus) and the dwarf nasturtium (Tropaeolum minus) are the most common in our gardens and shops. Garden nasturtium, also known as monk’s cress, is a cross of two South American species from Peru. Today, the hybrid is considered naturalised in South and Central America, California, Africa, Spain, France, Greece and the south of Great Britain.
Wild nasturtium species flourish on the sunny edges of riparian forests and on riverbanks. Tropaeolum is an herbaceous plant that forms trailing vines up to 3 m long. As the vines can both climb and hang down, the nasturtium is very versatile and can be used as a ground cover, as a climbing plant, as well as in a hanging basket. The disc-shaped nasturtium leaves are a bluish-green, have white leaf veins that connect to the central stem and average 5- 15 cm in diameter. They also boast waxy surface from which water simply rolls off. Another quality of this multi-talented plant is that both the nasturtium leaves and flowers are edible, with a sweet peppery flavour. While we mostly know this plant as the nasturtium, sometimes it is referred to as “monk’s cress” due to its petal formation, which looks similar to a monk’s hood. Nasturtium flowers come in a diverse range of colours and can be yellow, orange-red, pink, light purple, and even bicoloured. The pollinated flowers turn into seed pods, which you can gather and use like capers or save to plant next year.
Is nasturtium perennial?
In its native habitat, nasturtium grows as a perennial. However, due to its lack of frost hardiness, nasturtium is planted as an annual in Europe and the UK. But have no fear, it is easy to sow and grow these plants. In fact, they often even sow themselves.
When do nasturtiums flower?
Nasturtiums bloom quite persistently from early July through to autumn. Regularly harvesting the flowers will potentially extend this flowering phase even longer. Find out more about harvesting nasturtiums in our other article.
Are nasturtiums bee-friendly? Although it only produces a moderate supply of pollen and nectar, the herbaceous plant is nevertheless an important food source for wild bees and bumblebees.
Are nasturtiums hardy?
The nasturtiums that are commonly available in garden nurseries, do not tolerate sub-zero temperatures and are swiftly damaged by the first frost. Overwinter nasturtiums in frost-free, well-lit areas with temperatures of at least 13 °C. For particularly bushy or climbing specimens, prune the vines back to roughly 25 – 30 cm in length. To make overwintering easy, grow nasturtiums in pots or window boxes.
Once the nasturtium flowers wither, the seed pods will be visible. As soon as the seed pods are fully ripe, they are ready to be gathered and saved for later. Harvest the seeds when they are almost completely dry with a slightly brown colour. Do not collect the seed pods if they do not detach easily from the plant. Dry the seeds for a few days at room temperature, then store them in a paper bag in a dark and cool location for up to three years.
If you do not feel like collecting and saving the seeds, nasturtiums self-seed very well. Keep in mind that if you have several nasturtium varieties growing in the same spot, they will most likely cross-pollinate, resulting in offspring that are not true to the variety. As a result, new colour variations might appear the next year. If you wish to avoid being surprised with new crosses, propagate your nasturtium via cuttings.
That said, propagation by sowing is the simpler and less complicated method.
How to sow nasturtiums:
- Sow directly outdoors in mid-May
- Grow in small pots from March
- Fill pots with growing soil
- Plant 2 – 3 seeds per pot approx. 2 cm deep
- Keep substrate moist
- Germination temperature 20 – 25 °C
- Germination period approx. 7 – 10 days
- Plant nasturtiums out from mid-May onwards