Success with streptocarpus

Paul Johnson shares his growing tips

Pot up plug plants in a good houseplant potting compost – don’t use normal multi-purpose, which is too high in nitrogen. Use a ¾ depth pot – they don’t like or need a lot of compost because in the wild they grow on rock faces in ravines.

Streptocarpus are happy in any room, as long as they’re not in direct sunlight. They need to be placed on a windowsill to maximise light, but if the sun gets too strong, move them away from it. East or westfacing windowsills are ideal.

My watering test is to pick each plant up. If it feels light, it needs watering. I take it to the sink and water from the top letting the water drain all the way through. This flushes any excess salts out of the compost. There’s always a danger of over-watering if the plant’s sitting inside a ceramic pot cover and you water in situ.

During flowering, feed once a week with a high-potash feed such as Phostrogen or Tomorite. We sell tablets that you can push into the compost once a month.

In winter, put streptocarpus on a south-facing windowsill to soak up as much light as possible and water very sparingly. Most varieties stop flowering and you may see leaves forming abscission layers, where they turn yellow at the tips as the plant draws nutrients back into the crown. Just trim any untidy leaves.

Move potbound plants into bigger containers in spring, but only go one size up. You can keep a streptocarpus going for four or five years, but then they might get a bit woody. I recommend taking leaf cuttings in spring so you always have more coming through.

Keep pests such as greenfly in check with an application of SB Plant Invigorator, a non-toxic, environmentally friendly spray. Use it two days running for the best results, then weekly. It’s a foliar feed so it also strengthens the plants and protects them from mildew.