How to grow Streptocarpus

This page covers how to grow and propagate Streptocarpus.  These are the methods I've had success with here in New Zealand (NZ).
  1. General growing
  2. Leaf propagation
  3. Growing from seed
 
1. General growing information
The details given below are probably the ideal conditions, but I have found that Streptocarpus do quite well on either side of these optimums.
  • Soil = I use an ordinary commercial potting mix with a bit of perlite mixed in.  This makes sure the soil will retain some moisture but not get boggy. 
  • Temperature = 15ºC-25ºC.  I have found that Streptocarpus do not generally do well in much warmer temperatures.  In summer in Auckland, you need to find them a cool spot.  Summer in Wellington, NZ, is fine.  They can be taken down to 10ºC or less in winter for a rest.
  • Light = Medium to bright indirect light is best.  However, a bit of morning/late afternoon sun is more than OK.  Even in dimmer light, they will flower - just a bit less.
  • Water = I prefer to water only when the leaves have just started to wilt (or just before).  They easily recover from dehydration.  Make sure the pot has holes in the bottom to drain water, and never leave the pots sitting in a saucer of water.
  • Feeding = I feed occasionally with a "fruit and flower" or general fertiliser, which you can find at a garden centre.  Don't overdo it.
  • Seasons?  Streps require much less water in winter, so keep them quite dry.  Generally, Streptocarpus will flower from spring to autumn.  In winter, they will stop flowering and may lose some leaves, which is normal.  However some varieties flower in winter too!
  • Pruning = If you like, slice off yellowing or browned leaves at the base - these will be the older leaves naturally dying off. If there is a healthy leaf with some blemishing, you can successfully cut off only the blemished parts and trim the leaf to a normal shape.  With regards to flowers, snip off individuals as they finish, then snip the whole stem off at the base once the last flower on that stem is spent.
  • Pests and diseases = I find Streptocarpus to be generally pest and disease -free.  In NZ, I have occasionally seen them with aphids or mealy bug.  For aphids, I put the affected plant in a small enclosed space (like a cupboard), spray the air with fly spray, close the cupboard, then leave for 30 minutes or so (or just squash them).  For mealy bug, clean/kill them off with a bit of methylated spirits or isopropyl alcohol (rubbing alcohol) on a cotton bud.
 
2. Propagating from leaf cuttings
Streptocarpus grow easily from leaf cuttings, and there are a few methods to choose from.
 
Vertical leaf in soil:
  • Slice a strong, healthy leaf near the base of its stem with a sharp knife or scalpel, just above where the flowers arise.
  • Dip the base in rooting hormone (not necessary, as the leaves have built-in rooting hormones)
  • Place leaf upright in potted soil, a few centimetres down, gently firm soil around leaf.
  • Water lightly.
  • Cover in a plastic bag to retain moisture, poke a few holes
  • Place in temperature and light conditions mentioned above.
  • After a few weeks to a couple of months, one or more shoots will emerge from the soil.  You can either let the plant continue to grow like this, or you can separate off the plantlets and pot up separately for ongrowing.
Horizontal leaf in soil:
  • Take a leaf cutting as above
  • Cut the leaf lengthwise to remove the central midrib
  • Place leaf cut-side down in soil (either as a whole length or cut into smaller lengths)
  • Follow directions above 
Leaf in water:
  • Take a leaf cutting as above
  • Sit the cut end in water
  • Change water weekly
  • Over a few weeks to months, a mass of roots will form
  • Pot up the cutting.
 
Other leaf propagation methods can quickly increase the number of plantlets you have, but they will be very small and take longer to get to a decent size (see right).
 
You can also propagate Streptocarpus by dividing mature clumps.  And some varieties of Streptocarpus will produce plantlets below-ground from the root system.  You would see these when repotting, or sometimes they can grow out of the holes at the bottom of the pot.
 
3. Growing from seed
Streptocarpus hybrids do not grow true to type from seeds, but species Streptocarpus do.  This is the method I've had most success with.
  • Use ordinary commercial potting mix with a bit of perlite mixed in.  I have had considerably less success using 'seed mix' -type soil.
  • Spray the soil with water.
  • Scatter seed finely over soil.  Streptocarpus seed is very, very small, so you might want to mix it with a small amount of fine, dry sand to help scattering.
  • Do not cover the seed with any soil because it needs exposure to light to germinate.
  • Cover the pot with plastic kitchen wrap; poke some small holes into it.
  • Keep under continuous light (optional), or in a position with bright, indirect light.
  • Keep at about 20ºC (make sure the light/sun doesn't bake them).
  • Keep soil moist by gently spraying if necessary.
  • Germination times can vary, but expect it to take at least 1-3 weeks.
  • As the seedlings grow, enlarge the holes in the plastic wrap.
  • When seedlings are large enough to handle (say, leaves a 1-3 centimetres long), gently pot into larger pots.  Do this by gently digging them up and teasing out each seedling.
  • Given the right conditions, seedlings can bear their first flowers in about 6 months.
 Recently germinated seedlings
Germinated Streptocarpus seed
 
 
A seedling showing the usual unequal development of main cotyledon, and secondary rudimentary cotyledon
 
 
Leaf propagation methods, see Dibley's for full instructions


 
 
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