About the genus
Crassula is a large, diverse and widespread genus of succulent plants with well over 200 different species. There are also many hybrids and cultivars. The majority grow mostly in the Western and Northern Cape provinces of South Africa which are winter rainfall areas. Some are also found in the Eastern Cape summer rainfall zone and a few species may receive rain at any time. They can endure periods of drought, so they can survive on moisture from fog, mist and morning dew. Many enjoy the shade and protection of bushes but may also be found in the open, on plains, in and under cracks in rocks, in grit pans and on mountain tops. Different ones can often be found growing together and they invariably grow with other succulents such as mesembs.
Most Crassula are perennial but there are also annual ones. They are extremely variable in size and shape. Some are dwarf miniatures; others grow into larger bushes or small trees. A few are monocarpic, so die after flowering, and some grow from corms or tubers.
How to grow them
Crassula are quite tolerant and will grow in a greenhouse, on a windowsill or under artificial lighting. They need good light, especially when they are growing, but some sort of shading is often beneficial during the summer.
Either a mineral blend or a soil and grit mixture are both fine. Essentially the growing medium just needs to hold water for a short period before drying out, so needs to drain well and not stay wet for days. Standard plastic pots are fine. Whatever type of pot you choose, it need not be large. I grow my plants in 5cm (2in) plastic pots to start with, then pot on to something larger as required.
In the spring and autumn, with cool nights and warmer days, most Crassula are actively and visibly growing. During the longer days of summer, and the cold, dark days of winter, they prefer a ‘resting’ period. So, they need water while growing but little or none when resting. Those from the Eastern Cape will need some summer watering. Water well, but be sure to let them dry out between waterings and, if in doubt, do not water. When night time temperatures remain above 15°C (60°F) they shut down and will not take up any water, which can lead to root rot.
In spring and autumn Crassula produce lots of new leaf growth so appreciate some feeding, but how much depends on what growing medium you use. I recommend occasional half-strength low-nitrogen liquid fertiliser during these main growth periods.
Plants can suffer from mealy bugs both above and below soil level. Red spider mite can also appear and shows as browning of the leaves. Most available pesticides will control them. A more persistent pest is western flower thrips. They will feed on new leaf growth, leave ugly brown marks and are not at all easy to kill.
These plants in most cases will grow quickly and easily from leaves and cuttings. Leaves can be carefully removed from the stems and will produce roots and new plants from the heel of the leaf. Crassula seeds are rarely available commercially.
Text and photos by Chris Rodgerson, except Crassula arborescens (Marc Mougin).
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