The succulent pelargoniums from the winter-rainfall part of South Africa take on two guises: they can either be stem succulents or geophytes with subterranean tubers. In both cases the plants produce leaves during their winter growing season that dry up during their summer rest. This note concerns the tuberous species, most of which belong to section Hoarea, with just a few such as Pelargonium barklyi being in other sections. Most species have pastel-coloured flowers with darker guide lines for the benefit of visiting insects.
Fig. 1 P. incrassatum flowering on the Kamiesberge in September at the same time as other spring flowers
An exception to the pale flowers is P. incrassatum, which is a particularly widespread species, occurring in a variety of habitats from the Richtersveld south to the Vanrhynsdorp area. The vivid cerise colour of the flowers in the photos is the usual shade, but rose or salmon-coloured flowers occur in a few populations. This species has an unbranched flower scape whereas many other tuberous species produce ancillary flower umbels on side branches. Many of the Hoarea section species flower after their leaves have dried up in spring (April – early June). However, P. incrassatum is one of the first to flower, March in my collection, and still has a rosette of elongated deeply incised leaves at flowering-time.
Fig. 2 The foliage rosette of P. incrassatum in March with a well-developed flower scape going out of the picture and a second scape just forming in the centre
Repotting of tuberous pelargoniums is best done in August using a very gritty medium. Watering is started at the very end of the month and rosettes of leaves are soon produced. They are grown in frost-free conditions and watering is continued overwinter; a slight flagging of the leaves is a good indicator that water is needed. They start to dry up in April and watering is stopped as soon as the leaves are dry and flowering has finished.
Fig. 3 Flowers of P. incrassatum in cultivation
Propagation of P. incrassatum is from seed which is best sown in September, without artificial heat or polythene bags, as temperatures start to fall. Seedlings are treated like adults and should flower in about two years. Plants can be self-pollinated to produce seed, but you need to find younger flowers with ripe anthers and older flowers with developed stigmas for the pollen transfer.
Terry Smale
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