Streptocarpus

Streptocarpus are popular, relatively inexpensive, moderately easy-to-grow houseplants in a wide range of attractive colours which will produce flowers over several months. They are also easy-to-propagate.

Streptocarpus 'Bethan'

Quick facts

Common name Cape primrose
Botanical name Streptocarpus
Group Houseplant
Flowering time Spring to autumn
Planting time Any season
Height and spread 30cm (1ft) by 45cm (18in)
Aspect Bright filtered or indirect light
Hardiness Frost tender
Difficulty Easy to moderate

Cultivation notes

Streptocarpus (Cape primrose) are easy to cultivate in a well-lit spot in the house.

Spring/Summer

  • Keep in good light but do not expose to hot sun; an east or west facing windowsill is ideal
  • Plants in the greenhouse or conservatory will need some shade and good ventilation
  • Water regularly from March onwards. Plants can be watered from above or below, but don’t allow the pot to sit in water
  • Feed at two weekly intervals. Use a high potash plant feed at half strength from March to September or a specialist streptocarpus food
  • Remove dead flower stalks at their base

Autmn/Winter

  • Move to a south facing windowsill for maximum light, but move further away from the window at night if it gets very cold next to the window
  • Keep at normal room temperatures with a minimum of 7-10°C (45-50°F)
  • Plants in the glasshouse should be kept at a minimum of 5°C (40°F)
  • Stop feeding and only water when the compost is dry, plants may rot if the compost is too wet
  • Some leaves may naturally die back and can be removed
  • Crystal series plants may continue flowering so keep them in a very well-lit spot and continue feeding with quarter strength plant food

Potting-on

  • Plants can be potted-on if necessary in spring, using a specialist houseplant or multi-purpose compost
  • When re-potting choose a pot only slightly bigger than the current one, about a thumb's width wider in diameter, or one 'pot size' larger if using old-fashioned clay pots. A wide shallow pot or half-pot is more suitable than a deep pot.
  • After potting-on only resume feeding when the roots have filled the pot (i.e. appear at the base of the pot) 
  • In dry heated rooms that lack humidity, stand pots on a saucer of grit or expanded clay granules which is kept moist to increase humidity

Propagation

Leaf cuttings

  • Leaf cuttings are taken in spring or early summer choose healthy younger leaves from the centre of the plant
  • Cut across the leaf at 2in (5cm) intervals to give several sections; leaves can also be cut in half along the mid-rib
  • Fill a seed tray with a mix of equal parts peat free compost and perlite
  • Place the basal end in the compost about 1in (2.5cm) deep
  • Water well
  • Place in good light in a propagator, ideally heated, or cover with a plastic bag
  • New plantlets should develop in four to six weeks along the cut edges of the leaf segment
  • Once they are well rooted pot on to individual 3.5in (10cm) pots

Seed

  • Sow seed on the surface of a seed tray or pot of fine-textured seed compost
  • Do not cover, although to retain moisture cling film maybe used over the pot 
  • Keep between 21-24°C (70-75°F) in a greenhouse or on a windowsill, ideally in a heated propagator. Germination can take 10-14 days
  • Growth may be very slow at first 
  • When seedlings are established and have a true leaf, pot into individual pots
  • Feed with a balanced general-purpose liquid feed
  • From a late spring sowing plants may flower in 16-20 weeks

Division

Clumps of older plants can be pulled apart and divided when they are re-potted in the spring.

Cultivar Selection

Listed below is a selection from the huge range of cultivars available:

Streptocarpus ‘Harlequin Blue’: (Chelsea plant of the year 2010) The first flat-flowering bi-colour streptocarpus, with yellow on the lower petals making a striking contrast to the baby-blue upper petals. A compact plant with masses of flowers.

Streptocarpus ‘Crystal Ice’ PBR: Produces white flowers with blue veining all year round.

Streptocarpus ‘Falling Stars’ AGM: Light blue, veined flowers with a white centre.

The RHS is running a trial of streptocarpus in conjunction with Dibley’s Nursery in 2013/2014.

Links

RHS Find a Plant

Problems

Leaves: most trouble is encountered with the foliage;

  • Leaves rotting at the base is most likely due to wet conditions, such as impeded drainage, over-watering, compost too heavily firmed or the base of the pot sitting in water accumulated in the bottom of the pot-holder. Remove the rotting leaves and allow to dry
  • Oversized leaves indicate poor light and/or excessive feeding
  • Leaves may develop areas of brown or dead tissue leaf scorch due to too much exposure to sun
  • Ends of leaves die back in autumn or winter. This is a natural condition. Simply trim them off. Sometimes in winter an abscission layer can form causing a line across the leaf where the tip will go yellow and die but the base will stay green
  • Leaves wilting can be due to under-watering in which case water the plant, or over-watering in which case allow it to dry out. Wilting leaves can also be caused by vine weevil or root mealybug

Flowers: these are usually trouble-free.

When it comes to pests streptocarpus can suffer from aphids, glasshouse leafhopper, mealybug, tortrix moth, tarsonemid mites, sciarid flies and vine weevil. Diseases such as botrytis and powdery mildew are also an occasional problem.

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