Growing Streptocarpus
By Howard Drury DHE(Hons
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. Aeschynanthus and Achimines have recently been moved into the genusThere 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. Many rosette species are found in wooded ravines and valleys of the Drakensburg mountains of South Africa. The first to be introduced into this country was Streptocarpus rexii in 1826
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 have 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. 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. See also Fact Sheets 22 and 42.
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 original sized pot. Always restrict pot size and always use shallow pots to represent the effects of sitting in pools of rotting plant material collecting in undulations of rocks.
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. They may be watered from the top of the pot or allowed to soak up water from a saucer. Never stand them in water for more than two minutes. Streptocarpus are best kept on the drier side as wet compost can lead to root rots. Remember pot bound larger plants will need more water than small or recently up potted plants. During cooler periods and in winter reduce the amount of water given.
FEEDING - Streptocarpus require very little feeding, apply only half strength general liquid feed to the water once per month, during spring and summer. Alternatively Dibleys offer Streptocarpus fertilizer tablets that may be used once a month Avoid nigh nitrogen feeds, half strength tomato feed is acceptable being high in potash. Double the interval between feeds in the winter months even in warm conditions.
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.
Knowing their geographical distribution helps in understanding their care. They naturally come from the wooded areas on mountains, so they do not want the full intensity or heat of midday sunshine, especially in the summer here in the UK, but instead need a light position. Too much sun burns the leaves and fades the flowers.
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 streptocarpus 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 Baby Bio Leaf shine.
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 suitable and approved insecticide and cut off any severely infected flower stems. S B Plant Invigorator is a product sold as a tonic to enhance growth, but a side effect is in controlling pests and diseases and preventing future problems.
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 under surface 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.
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 pot on damp pebbles or 'Hydroleca' granules in saucer, and move away from 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.
CULTIVARS
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 from the early breeding days. Each year more varieties are introduced.
Kim - a medium sized plant, multiflowered, 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.
There are listed numerous other named cultivars, along with many true species.
Newer cultivars have the bonus of flowering over much longer periods and having shorter more manageable foliage.
Abergail
Alexis
Amy
Anne
Beryl
The list is endless so please follow this link for more details of cultivars available from Dibley as plug plant or larger specimens.
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.
S. johannis - this has large masses of dainty pale violet flowers with dark pencilling.
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.
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
There are few specific books on this fascinating group of plants, however Rex Dibley has written an excellent publication simply entitled Streptocarpus. Many of the better house plant books do have relevant sections on the subject. Best to conduct a web search for suppliers and best prices, also consider the second handbook dealers online who may offer some exceptional bargains. You will also find lots more information by conducting a web search.
Dibleys do offer some excellent fact sheets in PDF form giving much more information
Factsheet 1 - How to propagate your plants from leaf cuttings.
Factsheet 2 - Over-wintering streptocarpus plants.
Factsheet 3 - Propagating streptocarpus by seed.
Factsheet 4 - Streptocarpus: diseases and pests.
Factsheet 5 - How to treat your plants during the winter.
SOURCES OF SEED
Chiltern Seeds Crowmarsh Battle Barns, 114 Preston Crowmarsh, Wallingford, OX10 6SL England +44 (0)1491 824675
Dobies, Long Road, Paignton, Devon, TQ4 7SX. https://www.dobies.co.uk/
Mr. Fothergills Seeds. Gazeley Road. Kentford. Newmarket. Suffolk CB8 7QB. https://mr-fothergills.co.uk/ https://mr-fothergills.co.uk/pages/contact +44 (0)333 777 3936
S. E. MARSHALL & CO. LIMITED, Alconbury Hill, Huntingdon, PE28 4HY, UK https://marshallsgarden.com/ https://marshallsgarden.com/pages/contact-us +44 (0)1480 774555
Suttons, Woodview Road, Paignton, Devon, TQ4 7NG https://www.suttons.co.uk/
Thompson & Morgan Ltd.Poplar Lane, Ipswich, Suffolk, IP8 3BU. https://www.thompson-morgan.com/
SOURCES OF PLANTS - mail order service offered.
Dibley's Nurseries Cefn Rhydd Llanelidan Ruthin Clwyd LLl5 2LG http://www.dibleys.com/
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.
(C) 2023. This material has been produced by Howard Drury and must not be reproduced in part or full without the written consent of Howard Drury 8 Bagnell Road, Kings Heath, Birmingham B13 0SJ
JHD/6/10/2023
