Tropaeolum

These climbing and trailing herbaceous plants offer vibrant displays of colour, says Kevin Line.

T. speciosum - image: Floramedia
T. speciosum - image: Floramedia

Tropaeolum is a genus of between 80 to 90 species of annual and perennial herbaceous flowering plants, which originate from the cool mountainous regions of central and south America.

These delicate-looking climbing and trailing plants include Tropaeolum speciosum Award of Garden Merit (AGM), an exotic climber native to Chile, which is known as Chilean flame flower.

These attractive perennial versions of the Tropaeolum species display a marvellous finesse in the way they trail and climb over small hedging such as box, shrubs and other climbers.

I am currently cultivating a T. speciosum AGM over an Abies koreana AGM. The effect of the red flame flowers against the conifer, and mingling with the small cones, is outstanding. I carefully clip around the ones in the garden that are trailing over box hedges with hand sheers — this avoids any unfortunate sudden slips from a hedge trimmer.

The twining stems of T. speciosum AGM display simple and palmately lobed leaves. The flowers are funnel shaped and comprise five long-clawed petals — these often display a spur. The flowers are 2cm in width with rounded leaves made up of five to seven obovate leaflets.

These slender climbing plants can grow up to 3m in height and spread up to 1m within a period of five to 10 years. The bright electric colours of the flowers are followed by red and dark blue fruits in the autumn — these are positioned within the red sepals. This is a real connoisseur's plant.

T. speciosum AGM and other species work well as companion plants, mingling their trailing and climbing stems with certain species of clematis. And like clematis, these herbaceous climbers like to have their roots in the cool and their heads in the sunshine. The plants grow from tuberous roots and rhizomes, which prefer to settle in a south-, west-, north- or east-facing aspect, so part shade can be tolerated.

A leafy and humus-rich soil suits the tuberous roots of these plants, which prefer cool, moist summers. Some species, such as T. speciosum AGM and T. polyphyllum AGM, are winter hardy. In spring the dead growth can be cut to ground level to reshoot.

But T. pentaphyllum AGM and T. tuberosum are not winter hardy and their tuberous roots need to be lifted and stored in frost-free conditions.

T. peregrinum, known as canary creeper, has bright yellow flowers, which produces an elegant and impressive summer display. It is an annual, so is not frost hardy. It can grow to a height of up to 2m.

T. speciosum AGM can be propagated from seeds sown in the autumn into pots or modules of seed compost and placed into a cold frame. Germination usually takes three to four weeks, but can take anything up to two years. Rhizomes can be divided in spring before new growth begins. Most Tropaeolums resent root disturbance, and success can be varied.

Caterpillars, flea beetles and black fly can be a problem for these climbers, which can also be affected by a virus.

T. majus comprises hardy and half-hardy herbaceous annuals with trailing stems up to 1m. It originates in the Andes from Bolivia to north Columbia. The common name is nasturtium and it belongs to the family of brassicas — the leaves and flowers can be used to complement salads.
Nasturtiums remain a popular choice for summer bedding displays, baskets and containers.

The trailing varieties are excellent for growing in baskets and containers, while the bushy varieties produce arresting displays for summer bedding.

The vivid colours of red, orange and yellow, matched with the marbled foliage, creates an effective long-flowering summer display into autumn. They are easily grown in a sunny position, matched with a moderately fertile and well drained soil. The seeds can be sown in mid-spring where they are to flower, or seedlings can be planted out after the risk of frost.

Nasturtiums are useful as a companion plant, which helps to repel whitefly.

One downside is that T. majus may be attacked by aphids or caterpillars, which brings the flowering displays to a sudden halt. That aside, it's worth every effort to have these plants adorn the garden.

 

What the specialists say

Nick Haworth, head gardener, Garden House, Yelverton, Devon

T. speciosum AGM does particularly well at the Garden House. It is planted in the shade in acid loam beneath rhododendron, azalea and pieris. It reliably overwinters and comes up in late spring to scramble up to 3m through the shrubs to give a brilliant display of scarlet flowers from midsummer onward. It gently spreads by means of root division, which is the most reliable way of propagating it.

Young plants will need protection from slugs. It can be propagated from depulped seed sown in ericaceous compost, but this is challenging as it should not be allowed to dry out and be kept for a couple of months. After this, seeds are then chilled for three months to break dormancy.


In practice

Beverley Rogers, Endsleigh Gardens Nursery, Milton Abbot, Devon

T. Speciosum AGM have an extensive root run, which favour being planted in a friable soil with the addition of a good supply of leaf mould. This will encourage the plants to root up and around other plants.

Richard Hopkins, plants manager, Applegarth Nursery, Chipping Norton, Oxfordshire

We grow two popular nasturtiums — 'Tom Thumb mixed' and 'Empress
of India'. 'Empress of India' — the most popular of the two — has a darker coloured leaf and is excellent for cottage gardens. It is free flowering and easy to look after.

We sow direct into 9cm pots — germination is quick and reliable. The plants are excellent for drawing in pollinators, so it is a good choice for wildlife gardening.

Steve Dance, Burncoose Nurseries, Redruth, Cornwall

T. speciosum AGM have lovely bright flowers which are best planted at the base of a shrub. They will then scramble through from the shade into the sun and produce brilliant red flowers.


Species and varieties

T. tuberosum 'Ken Aslet' AGM (H3) is a tuberous plant that likes to be planted in the shade at the base of a shrub. It will then grow through into the sun, producing orange flowers. It dies down in the winter. It is worth checking to see if the tubers need replanting a little deeper and add a mulch for winter protection.

T. pentaphyllum is a delicate but rampant tuberous climbing species with purple stems and leaf stalks. The 4cm leaves are deeply cut into five divisions. Soft red flowers, 2-3cm, with long pink spurs and green interiors spotted in red, are followed by bunches of dark blue-black berries.

T. polyphyllum AGM (H3) is a spectacular scrambling and trailing — rather than climbing — species, which makes a mat up to 1m across. From a long, slender, deeply growing tuber, the stems emerge. They are usually prostrate and radiate across the soil.

T. speciosum AGM (H5) is a delicate, perennial climber for cool climates. Deep-rooting, thin white rhizomes produce slender stems with green hairy 4cm leaves, each with up to seven notched, wedged shaped lobes. The long-spurred 3cm flowers are bright scarlet and followed by blue-black fruits.

T. tuberosum has red or purple-tinted stems which grow from large purple-marked, yellow tubers, that are potato-like and edible. Three- to six-lobed, bluish-green leaves, whose long stalks clasp their supports, carry from their leaf joints 3-4cm showy scarlet and yellow, cup-shaped flowers with scarlet spurs on slender stalks from August to the frosts.

T. majus 'Empress of India' is a classic compact, non-trailing variety. It looks sensational. The foliage is dark bluish to green. The flowers are an intense crimson-scarlet. This variety has been awarded the first-class certificate of the Royal Horticultural Society.

T. majus 'Jewel of Africa' is the climbing equivalent of Alaska, a popular variegated dwarf nasturtium. The foliage is cream marbled and striped, giving an attractive display. Lovely flowers are produced above the leaves— it is striking to see them from a distance. Nasturtium colours of yellows, creams, reds and peach- pinks, plain and blotched. It provides great displays for baskets and containers, and also for climbing.

T. majus 'Tom Thumb mixed' is a classic variety in cultivation for at least 100 years. Dwarf compact plants bear single flowers in a wide range of cheerful colours.

T. majus 'Alaska' AGM (H3) is a must for those who like variegated plants. This fascinating dwarf nasturtium comes almost completely true from seed. The attractive leaves are blotched with pale green, producing a variety of abstract patterns, leaving some almost devoid of green. The flowers are in a range of bright nasturtium colours.


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