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Tropaeolum

Tropaeolum

The scientific name for Nasturtium is Tropaeolum majus. Virtually every garden centre stocks the seed of this annual climber. Nevertheless there are some 90 known different Tropaeolum species of this South-American genus, subdivided into annuals and perennials. They are mostly climbers with tuberous roots or rhizomes.

I first discovered this genus at the botanic gardens of Göthenburg, when, in the alpine house, a Tropaeolum brachyceras – the golden-yellow flowers which flowed over it like a waterfall – caught my eye. I soon fell under the spell of these wondrous plants and started building up a little collection of my own. By now, I feel I’d like to share the discoveries I have made by describing some of these species.

The genus Tropaeolum occur in the cooler mountainous regions stretching from Mexico to Patagonia. A general characteristic of these plants is that most species have plump tubers or rhizomes and their rounded leaves are usually deeply notched. The solitary flowers have five sepals, the uppermost with a brightly coloured and distinct spur and all flowers have five stalked petals.

They multiply by developing fresh tubers or through seeding. Some plants have viable seeds that must be sown as soon as possible after harvesting. My experience is that seed obtained in winter is best sown indoors. The seed-pot is best kept at room temperature for a month or so. It is then best stood outside in the garden. Germination takes place as a result of change in temperature. If the seeds did not germinate during this first winter however, it is unlikely that they will ever germinate. It is possible to propagate a few species by rooting stem cuttings, taken from material that is not too soft.

T. speciosum

One of the more striking members of the entire Tropaeolum genus. The leaves are almost entirely covered by a mass of bright red flowers. In its natural state, this species is found in the temperate rain forests of Southern Chile, at an altitude of +/- 1000 m.

This climber – growing to 3m. (occasionally reaching up to 5m.) in height – develops from branching plump rhizomes, which are approximately 3 mm in thickness. It is sufficiently hardy provided rhizomes are planted at a depth of +/- 30 cm. It prefers a not too sunny spot and a nutrient rich, slightly acid soil, that never dries out. It is recommended therefore to keep the soil sufficiently moist, particularly during its first year. The plant can be multiplied by rhizome division.

T. ciliatum

Mostly occurring in the woods covering Chile’s mountain slopes, in between l000 to 2000 m. It is divided into 2 subspecies, mostly depending on their geographical location. The flower of T. c. ssp. septentrionale has a larger spur than its T. c. ssp. ciliatum’ counterpart.

Characteristics are similar to the previously mentioned species, but the colour of the flowers is light to dark yellow and they are veined with reddish-brown.

These plants are less choosy in the type of soil they require. Once established, they tend to spread quite aggressively and need to be kept in check. They require sufficiently moist conditions during the summer and their leaves should be sprinkled with water at regular intervals. They can be multiplied through simple rhizome division.

T. polyphyllum

It is found in screes of the Andes, in Chile and in Argentina, between 1000 to 4000 m. in altitude. The tubers go burrowing to amazing depths, in order to escape frost damage.

All those who paid a visit to the Herman van Beusekom’s nursery during the summer will certainly have noticed this plant with his golden yellow flowers.

Some varieties in the wild have orange and lemony yellow flowers. Those plants found at the higher altitude of their favourite breeding grounds, are very compact.

Unlike to most of the members of this genus, they are not climbers but develop pulpiest branches some 60 to 100 cm long, spreading openly on the ground. They are covered in shimmering grey leaves. The tubers are best planted in the garden, at some 30 to 50 cm. in depth. They then may be considered fully winter hardy. They should nevertheless be protected with glass to keep the roots from rotting. They need a well drained soil in a sunny position. The plant must be provided some shelter since its branches easily break in strong winds. The flowering period is June – July. It also soon dies down into a short resting period after flowering. It can only be replanted when at this stage. It can be multiplied from developing fresh tubers or by seed.

T. incisum

Is found wild in Argentina, on the slopes of volcanoes, in between 850 to 3000 m.

The characteristics of this species are quite similar to the previous mentioned.

The difference is mostly in the size of the yellow or orange flowers and the shape of the leaves.

They are also grown in a similar fashion. They may be slightly more difficult to cultivate as the tubers are inclined to rot.

T. sessilifolium

A low climber (up to about 50 cm) found in the more arid zones of the hill slopes of central Chile, in between rocks and bushes (2000 – 3000 m.).

The plants have smaller leaves but their flowers are large and a whitish light pink in colour.

They require a very well drained soil. They may not be entirely winter hardy.

T. tricolor

Is widespread throughout the misty coastal areas, right to the top of the of the Andes, in Bolivia and in Chile.

This fairly small climber has oblong to rounded roots. The period of growth begins in the autumn (October / November). A mass of orange reddish flowers appears during the spring. They display yellow corolla petals around the eye of the flower. Winter hardiness depends on the origin of the plants. Nevertheless they are best kept in an alpine house. The amount of flowers depends a little on the minimum temperature in the winter.

T. azureum

It natural dwelling place is in between bushes in arid areas of Andean foothills in Northern Chile.

It is the only blue variety of the entire genus. The plants are characterized by very fine stems and rather narrow leaves. Purple-blue flowers with a white heart appear on this 100 cm. high climber. The species is not winter hardy. I keep tubers in deep pots filled with a sufficiently airy compost blend. The plant starts to develop in September and will flower during the spring or in summer. One of the problems of this species is that its tubers stay dormant for considerable periods, sometimes over 4 years or more. This may also be the result of tubers getting very short resting periods only. If tubers are kept too dry at such a stage, root development will suffer. Tubers therefore are best re-potted as soon as the leaves have died off, keeping the soil only very slightly moist.

But what a graceful sight this plant is, certainly when one manages to find a deep blue clone!

T. hookerianum

Is endemic to a small area of the misty central Chilean coast.

This climber reaches 60 – 100 cm. in height. The origins of the plant explain why it is not really winter hardy (not below –5°C). This species needs to be cultivated along the lines of the former, and presents similar problems.

T. hookerianum is divided into 3 different subspecies.

T. h. ssp. hookerianum has bright yellow flowers.

T. h. ssp.pilosum has distinctly hairy flower stalks.

T. h. ssp. austropurpureum has purple-like flowers, as its name will indicate.

T. brachyceras

This yellow flowered climber, some 100 cm. in height, comes from the dry coastal areas of Chile.

The plants must be kept in a frost-free alpine house. They are cultivated in the way of the two previously mentioned species.

T. pentaphyllum

Is widely found in the temperate regions of South-America.

This climber attains some 2 m. in height. Its flowers tend to be rather small and less obvious. They are a pinkish red and green in colour.

Tubers are best kept in a large pot, filled with well-drained compost, rich in humus. The tubers start growing towards the end of the autumn. Even though the plants can take a little frost, they are best kept in a frost-free alpine house. They can be put out in the open in the spring, in a sheltered sunny spot. They appreciate a little liquid fertilizer at flowering time. This is also true for the remaining Tropaeolum species.

T. tuberosum

In the ancient realm of the Inca’s, the roots of this plant, together with potatoes and a few more tuberous plants, were cultivated as food. They were further used as medicine against liver and kidney diseases.

This species originates on the hillsides and in the valleys of Peru and Bolivia. It reaches some 3 m. in height. It is not really winter hardy. The plants have greyish green leaves and reddish-orange flowers. Tubers must be planted during the spring at 12 to 15 cm. in depth, in humus rich soil. Preferably in a sheltered spot, next to a wall to keep the plant’s roots in the shade. The tubers are lifted out of the soil towards the end of autumn and kept well away from frost. The plants will start flowering when the day-length are decreasing. This means in our country that, flowering does not start before the first nights of frost appear. The most famous clone ‘Ken Aslet’ will flower a little bit earlier and so has less problems over frost damage.

T. rhomboideum

Comes from the sub-alpine region of the Andes in Chile, at some 1000 – 2000 m. altitude. The plants attain 30 to 100 cm. in height. They have yellowy-orange flowers. In their natural state, they are found on well-drained soils that are covered with snow in winter. My own plant is no more than a year old and has not flowered as yet.

T. x tenuirostre

This natural hybrid occurs in the region of Central Chile where T. brachyceras and T. tricolor overlap (1500 m). It consequently is only slightly winter hardy and needs the same care as its parents. The plants attain 1 to 3 m. in height and have yellow to greenish-yellow flowers.

T. beuthii

Occurs in arid and frost-free coastal areas in Northern Chile. It reaches some 100 cm. in height and has fairly large yellow flowers. It is closely related to T. brachyceras and T. hookerianum.

I hope that through these notes I have managed to arouse some interest in these wonderful climbers. They may not be altogether at home in a rockery but they are certainly worthy of a place in the garden or in the alpine house. They will reward you with a virtual whirlwind of colour. I can only hope nurseries eventually include all the known species in their catalogues.

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