The Cape Primroses, as streptocarpuses are called, are very attractive greenhouse perennials of which fine hybrids have been developed. The, whose colours include purple, blue, violet, red, pink and white, are trumpet shaped and are borne in clusters on 18-in. stems well above the foliage. The main flowering season is summer and autumn, but blooms are borne intermittently for most of the year. Provided one can maintain a minimum temperature in winter of 10°C. (50°F.) these are delightful plants to add to one’s collection. Splendid as the mixed hybrids are. I must say that my favourite streptocarpus is the named variety Constant Nymph. This has lovely mauvish-blue flowers and with warm greenhouse treatment it will remain in flower for most of the year.
Seeds are sown in January or February in pots or pans filled with seed compost to provide plants for autumn flowering and a July sowing will provide plants for flowering during the early summer of the following year. Sowing in March or early April will mean savings in fuel costs over earlier sowing but the plants will, of course, be later in coming to maturity. A temperature of 18°C. (65°F.) is needed for successful germination.
Prick the resulting seedlings out into boxes of John Innes No. 1 Potting Compost and pot them into 3l-in. pots before they become overcrowded, using a similar compost mixture. Later, move the plants on into 5-in. pots of John Innes No. 2 Potting Compost.
During the hottest part of the day from May onwards streptocarpuses need some shade from strong sunshine, particularly from about 10 am. to 3 to 4 pm. Airy conditions are also needed at this time of year and frequent spraying overhead with clean water to maintain a moist atmosphere. A temperature of 16 to 21°C. (60 to 70°F.) should be maintained throughout summer.
Watering and Feeding
Water freely and start feeding with weak liquid manure as soon as the plants begin to fill the compost in their final pots with roots.
During the winter the plants can be allowed to become really dry so that they are almost dormant or resting. By late February or early March they will be starting to make new growth and the water supply should then be increased gradually to meet the full requirements of the plants.
When growth restarts, the plants should have some of theshaken from their roots and new John Innes No. 2 Potting Compost added in its place.
I have already explained about raising streptocarpuses from seed, however they can also be increased by dividing mature specimens in February or March into separate crowns with roots attached. These are grown on in exactly the same way as seedlings. New plants can also be raised by leaf cuttings. These should be prepared by removing a complete leaf and inserting the leafstalk and lower portion of the leaf in a pot of cutting compost in a propagating frame with a temperature of 18°C. (65°F.).