A species with a quirky seed germination process that should appeal to Lowveld smallholders is the Lowveld Chestnut, Sterculia murex.
It is a fascinating species, restricted in nature to the terrain surrounding the granite inselbergs in and between Mbombela and Barberton, with some populations in the Kruger National Park.
In habitat the trees can be very common, but they are a species of restricted range and relatively uncommon in cultivation.
The trees are a bit reminiscent of a cabbage tree (Cussonia sp.) in looks, with large, five lobed leaves. The trees can get large but in their younger years are fairly slender without much spread to the crown.
The roots are large and fleshy, and can be damaging to paving.
Blossom tree
A “blossom tree”, the species bears lovely yellow spotted-with-orange flowers in spring for about two weeks.
If the winter has been cool and sufficiently dry the blossoms will appear on bare branches, but if the tree has had winter water it is inclined to be semi-evergreen, lessening the show.
The tree gets its name from its large, spiked fruit which look a little like those of a “true” chestnut, Castanea sp, as well as its edible, large, sweet and oily seeds, or nuts, which are roasted for consumption in much the same way as the European winter delicacy.
Interestingly enough, the Latin species name murex, derives from the Latin name for a spiked war club, also referring to the fruit.
Heavy bearers
The trees can bear very heavily, and the fruit are shed in February/March over a short period which coincides with the wettest time in the plant’s habitat’s rainy season.
Nuts are very heavily eaten in habitat, as they are delicious both raw and cooked.
Mature pods just starting to open end February. Courtesy Jason Sampson
They have soft, leathery shells that offer little protection against herbivores, and if roasted in a pan or over the coals of a fire, will “pop” slightly, showing the flesh of the seed.
A word of caution: the inner rim of the fruit bears short, irritating hairs which necessitates some care when harvesting the nuts.
The tree is adaptable and can be cultivated, but prefers a warm climate with good summer rain.
It bears best if given a good dry season, and is adapted to long periods of drought in winter.
It does not appreciate temperatures much below 0 deg C but can re-sprout from its succulent rootstock (caudex) if cut completely back by black frost as a seedling.
Adult trees can take colder winters.
Fast growing
Very fast growing, the tree can start bearing pods in its fifth year, possibly earlier if fertilized heavily.
Growing from seed can be quirky, and one needs to understand this tree’s adaptations to its unique habitat to get an appreciation of why the seeds do what they do.
When shed in Pretoria (where Sampson studied and propagated the species), the seed dries out and dies in hours sometimes. That is due to the fact that the seed shell has no water holding ability whatsoever.
In habitat the seed would have been shed in almost monsoonal rain and, if lucky, be flung between rocks by the breaking up of the falling fruit, where it will be protected from predation long enough to germinate, which it does and completes in a handful of days.
Also, Sampson adds, “when trying to propagate this species from hours-old seed in Pretoria, I almost discarded seedling trays full of empty seed shells thinking they had been eaten by rodents (which can happen), but by pure luck figured out that the seed had germinated at lightning speed and made storage organs (an enlarged rootstock or succulent caudex), and thick, fleshy roots as deep as possible in the trays.
These rested a full winter before shooting the above-ground parts of the young trees.
”So in habitat, these seeds are optimized to “get underground” as fast as possible to escape being eaten, and the fires and drought that follow in winter.”
Pods are full of large and soft shelled, oil rich nuts. Courtesy Jason Sampson
Storing seeds and nuts
If you are into seed saving and sharing, says Sampson, always propagate from the freshest seed possible.
If harvesting nuts for propagation, storing them in plastic or a sealed container is recommended, but they will show signs of germination very soon, and need planting in soil that is kept moist for the duration of the process.
Sampson has managed to delay germination by about a month by storing seed at 10 deg C, but they have no dormancy so that was probably about the maximum.
Seed trays can be kept relatively dry over the plants’ first winter, and caudexes can be separated and potted up in Spring.
Sampson has never tried to propagate this species from cuttings.
It is likely to be possible but caudiciform plants will often not generate a caudex from a cutting and since this tree seems to depend heavily on this structure it may affect its performance.
He has noticed some differences in performance both in habitat and cultivation, and recommends that one grow nuts from heavily bearing trees to get offspring with increased potential to bear well.
Food forest
The Lowveld Chestnut is admirably suited to a food forest, and may well have potential for commercialisation too.
The nuts store very well if frozen, and cultivators with an experimental turn of mind may think about the potential for nut flours, nut milks and nut oils, to name three potential areas of experimentation.
Harvest the nuts as soon as possible from the moment the fruit opens.
Depending on where you live in the country they can dry out, be eaten by herbivorous animals or nut eating birds, or all of the above.
For more information on this contact Jason Sampson at jason.sampson@up.ac.za.
Read more posts about other unusual crops here.
Main image: Blossoms of Sterculia murex appear in huge numbers in spring. Courtesy Jason Sampson