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Growing Streptocarpus

By Howard Drury

ORIGINS

The streptocarpus comes mainly from South Africa, hence the common name Cape Cowslip, but also is found in Burma, Thailand and Madagascar. Between 1850 and 1940 some eighty species were found and introduced, from which the modern hybrids were raised. Streptocarpus are members of Gesneriaceae, the same family as Saintpaulias. There are several not well-known wild species, often with quite small dainty flowers more akin to African violets or freesias than the better known large flowered hybrids. These wild species fall broadly into two groups, in that some plants have definite stems, so forming small bushy plants, e.g, Streptocarpus saxorum. Others, such as the modern hybrids, produce a basal rosette of leaves, Most of these rosette forming species originate from wooded shady areas, giving indications as to their basic requirements and care.

In the l960's many of the available hybrids had large, somewhat foxglove like trumpets nearly 3" across and 3" deep, in various shades of blue, purple and violet. These were often streaked with marbled white lines leading up into the trumpet, and overlaid with a deep velvet sheen, particularly in the deeper shades. There were also a few cultivars available in shades of pink, pale‑brick-red through to magenta red, again usually with marbled white lines. Unfortunately, these plants were invariably quite gross, the long heavy foliage being far from elegant and unsuited to modern homes.

However, there was available, but not so well known, a much more dainty, smaller flowered hybrid, with large numbers of plain pale blue flowers, and more acceptable sized leaves. Raised and released by J. Innes Institute in 1947, were as a result of a scientific breeding programme to overcome the shortcomings of the larger unacceptable cultivars. Still available and now much more appreciated, 'Constant Nymph' has been the springboard to the development of the modern Streptocarpus, in a wide range of new pastel colours. The long strap like leaves has been bred out, and replaced with broader, shorter, less brittle foliage making the plant more attractive. Plants will produce successions of flowers throughout the spring and summer for three or four years. After which plants should be discarded as they become tired, new ones being easily raised from seed or cuttings.

 

PROPAGATION

Plants are easily raised from seed sown onto the surface of a peat based or peat free compost. Water from below to avoid disturbing the very fine seed, and place in a temperature of 18C (64F). Once seedlings appear they can initially be grown on in a shady position in the glasshouse, in the seed tray until large enough to be individually potted up. Always ensure that the seedlings do not dry out, the compost being kept moist but not wet.

New plants can also be propagated from leaf cuttings, taken during spring or summer. A complete leaf should be removed from the parent plant, and either with the leaf laid upside down on a soft surface cut down the middle of the central vein from end to end or cut across the leaf at 35 ‑ 50mm (1.5 ‑ 2") intervals. Where possible, cutting material taken from the bottom end of leaves should be used, as they produce new plants more readily. Cuttings can then be inserted in a peat/sand/perlite cutting compost in seed trays.

© Howard Drury, Lark Hill Retirement Village

 

Rooting powder maybe dusted along the central vein, in method one, or on the lower cut surface in method two. Use a plant label or similar to make a shallow depression into which the cuttings are shallowly inserted. Water and then place in a propagator or polythene bag. Maintain temperature of l5C (60F) and never let the compost dry out. New plants will appear after about 4 weeks along the central vein or where the veins were cut through.

POTTING UP/POTTING ON

Young plants should be potted up when large enough to handle, divide young plants growing on the leaf cuttings into single plantlets. Older plants should be repotted each spring after teasing or washing away some of the old soil, even if repotting back into the original sized pot.

SOIL - peat based or low-peat composts are best, as these retain moisture but allow good drainage.

WATERING - two to three times a week during the summer months, but do not stand plant in water or roots will rot. During the winter, water once a week or less, especially if temperature drops below l5C (60F). Always let surplus water to drain away after watering.

FEEDING - Streptocarpus require very little feeding, apply only half strength general liquid feed to the water once per month, during spring and summer.

HUMIDITY - Streptocarpus are best grown in a humid atmosphere. It is a good idea to stand plants on damp pebbles or on a capillary sand or matting bench if in the greenhouse to give a constantly humid atmosphere during the summer months. Keep drier during the winter months.

LIGHT - good light is essential, but constant bright sunlight should be avoided. A north or east facing window is ideal. Under the staging in a greenhouse is well suited to streptococcus during the summer months. In bright situations, it will probably be necessary to provide some shade from midday during summer.

TEMPERATURE - a minimum of l5C (60F) is ideal during the winter, but Streptocarpus have survived lower temperatures if they were kept drier and almost dormant. During the active growing period of spring and summer, 18 ‑ 21C (65 ‑ 70F) is ideal, above 24C (75F) plants will suffer.

CLEANING - occasionally brush dust off leaves with a clean soft dry paint brush, never use a wet cloth or Leafshine type products.

DEAD HEADING - always remove faded flowers and cut off flower stems as low in the base of the plant as possible using a sharp knife or by giving a sharp tug.

PLANT PESTS

Greenfly and whitefly, greenfly spread rapidly up the young developing flower stems, and into the opening flowers, causing distortion and stunting. Spray with a systemic insecticide and cut off any severely infected flower stems.

Mealy bug, if these plants are grown in a mixed collection of flowering and foliage plants, there is high probability they will collect an infestation of this very persistent, unsightly pest. Feeds in clusters on the rough undersurface of the leaves close to the midrib, also deep down in the rosette on the developing leaves, where it is safe from easy access. The soft texture of the foliage precludes the safe use of an artist’s paint brush dipped in methylated spirit as a means of control. There are virtually no chemical methods of controlling mealy bug. Repotting is recommended after washing the old compost off the roots, along with any pests. This is best done during the active growing season from April to late August.

PLANT DISEASES

Botrytis, especially in winter, results in whole leaves and even complete plants rotting off, if temperature too low and compost too wet, move plant to warmer place and reduce watering.

OTHER PROBLEMS

Leaf scorch - margins brown and crisp, caused by plant and/or its surrounding atmosphere being too dry. Water more frequently, stand the pot on damp pebbles or 'Hydroleca' granules in a saucer, and move away from the top of that hot central heating radiator under the windowsill. The very long leaves of the older hybrids are brittle and therefore easily damaged, the mid-ribs easily cracked and the margins torn.

NAMED CULTIVARS :- the majority of streptocarpus available through the pot plant trade, are not supplied as named specimens. The more discerning grower will therefore have to obtain their plants from specialist nurseries. The following are just some of the listed named types. Each year more varieties are introduced.

Kim - a medium-sized plant, multi-flowered, small deep inky blue flowers.

Heidi - clear blue, deep purple markings on lower petals.

Mini Nymph - a compact free flowering version of the ever popular "Constant Nymph", violet blue with deep violet veins and a creamy throat.

Nicola - this, and "Winifred" are different from the other hybrids, in that the flowers are semi-double. Nicola is early and very free flowering, deep pink. Leaves more upright than the usually spreading habit of most Streptocarpus.

Rosebud - the first fully double Streptocarpus. Large deep pink, ruffled flowers, with a cluster of extra petals in the centre. A strong grower.

Sandra - large mauve flowers, with tracery of deep purple veins on the lower petals, leading towards a yellow throat.

Susan - dwarf plant of rounded habit. Each stem carries many flowers, of intense magenta with yellow centres.

Tina - another compact cultivar, the flowers having pale pink upper petals, the lower being magenta with distinct veins.

In later years extensive breeding programmes at Dibleys Nursery gave rise to two lines of new plant introductions. There were the much-improved John Innes hybrids which are brighter coloured and larger flowered over more compact foliage. They will relist their varieties in late spring each year.

The second introduction has extended their flowering period. There are typically carry the word Ice in their name to denote this very exciting development.

Crystal Ice with delicately veined hints of purple to lilac on lower petals over rich dark green foliage.

There are listed some 30 or more other named cultivars, along with many true species.

WILD SPECIES - these Streptocarpus are not as flamboyant as the hybrids listed later, but nevertheless have a delicacy and elegance that make them worth growing.

S. candidus - one that produces large inflorescences of small white flowers with a blue mark on the lower petals. These also have a pleasant honey scent.

S. caulescens - rich brown upright stems bearing a mass of small purple flowers resembling violets.

Streptocarpus cyandrus

 Streptocarpus dunnii

 Streptocarpus galpinii

 Streptocarpus glandulosissi - stemmed

 S. johannis - this has large masses of dainty pale violet flowers with dark pencilling.

Streptocarpus kentianensis

 Streptocarpus pallidiflorus

 Streptocarpus pentherianus

S. primulifolius formosus - quite large flowers with distinct petals, pale mauve with a spotted yellow throat, giving a very delicate effect not unlike an orchid.

Streptocarpus rexii

 S. saxorum - long trailing stems, small fleshy leaves and pale-blue flowers. Very attractive in hanging baskets.

S. solenanthus - flowers almost white with pink and red markings on the lower petals.

HYBRIDS - These are the more commonly seen houseplants that can be grown from seed. They consist of the brightly coloured, large-flowered types that are usually sold as unnamed varieties and are simply labelled as Streptocarpus or "Cape Primrose". The varieties listed below are available through the larger seed catalogues.

Royal Mixed - freely produced large blooms of deep pink, blue, red and white with large-veined throat.

Fiesta Mixed - long flowering variety in an array of pastel colours.

Sublime - the usual colour range of pinks and blues, with the addition of a beautiful red.

Baby Blue - lavender blue with dark stripes. Ideal in 3 inch pots as a table decoration, also an alternative to African Violets.

Lipstick - bright warm shades of red and pink, including white with a red striped throat.

Windowsill Magic Mixed - striking purple, blues and pink veined throats on exquisite cream, pink, blue, violet and white flowers. Ideal for the beginner as it will flower within 4 months of sowing.

 Concord - neat, compact plants flowering from August onwards, with excellent mix of colours.

Melody - early flowering, satiny trumpet-shaped blooms in deep shades and pastel hues. Long lasting flowers produced 5 months after sowing.

 

FURTHER READING

Streptocarpus by Rex Dibley 164 pages 2008 ISBN 0954446828

Social media groups for streptocarpus Facebook Streptocarpus Club 3.5k followers!

John Innes Institute who were largely responsible for much of the earlier work on Streptocarpus hybridus

 

SOURCES OF SEEDS AND PLANTS

Dibley's Nurseries  (Brilliant website with loads of excellent information) mail order service offered. Also sold through retail outlets such as Ashwood Nurseries and by Dibleys at major flower shows throughout the UK Llanelidan Ruthin Clwyd LLl5 2LG

Main website list all their plants                Their Care guide to Streptocarpus

Dobie’s Seeds seeds only

Nicky’s Nursery seeds only

Sutton’s Seeds seeds and plants

Thompson and Morgan seeds and plants

 

The information given in this fact sheet is provided in good faith. It is however of necessity general information and advice on the topic Howard Drury shall be under any liability in respect of the provision of such advice and information and you are strongly advised to seek independent advice on any particular gardening problems or queries you may have, preferably from experts who can (when appropriate) inspect the problem before providing advice.

© 2023/12/06 . This material has been produced by Howard Drury and must not be reproduced in part or full without the written consent of Howard Drury