#GROW

The quirks of growing Lowveld Chestnut

FEB 16, 2023  | Written by Jason Sampson. Photos by Jason Sampson, Rob Palmer, @qgrobler, @jpot123 (iNaturalist)

Above: Lowveld Chestnut is a fast-growing tree and can already start bearing fruit in its fifth year. Photo by Rob Palmer, iNaturalist

I have a long history with this wild food plant species and undomesticated crop, which has such huge, untapped potential, and know all its moods. In fact, the following information on the quirks of its seed germination, and observations of this in habitat has only ever rarely, if ever, appeared in print.

I’m referring to the Lowveld Chestnut (Sterculia murex).

The Lowveld Chestnut is a fascinating species restricted in nature to the terrain surrounding the granite inselbergs in and between Nelspruit and Barberton with some populations in the Kruger National Park and Eswatini. In habitat they can be very common, but they are a species of restricted range and relatively uncommon in cultivation.

The trees look rather like the cabbage tree (Cussonia sp.), with large, five-lobed leaves. They can certainly become big trees, 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.

A “blossom tree”, the species bears lovely yellow and 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.

Above: Blossoms of Sterculia murex appear in huge numbers in spring. Photo by Jason Sampson

Where does the name come from?

The tree gets its name from its 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. These can be roasted to eat 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.

The trees can bear very heavily, and the fruit are shed in February and March over a short period. This coincides with the wettest part of the rainy season in the Lowveld Chestnut’s natural habitat.

Nuts are very heavily predated on in habitat, as they are delicious both raw and cooked. 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, though: The inner rim of the fruit bears short, irritating hairs and you should be careful when harvesting the nuts.

Above: The plant gets its name from the fruit: ‘murex’ derives from the Latin name for a spiked-war club, as this picture proves. Photo by @qgrobler, iNaturalist

Cultivating Lowveld Chestnut: Get the conditions right

The tree is adaptable 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.

Lowveld Chestnut does not appreciate temperatures much below zero degrees Celsius but can resprout from its succulent rootstock (caudex) if cut completely back by black frost as a seedling. Adult trees can however handle colder winters.

Very fast growing, the tree can start bearing pods in its fifth year, possibly earlier if fertilized heavily.

You’ll come to know all the quirks of this species when you grow it from seed. But it’s helpful to understand this tree’s adaptions to its unique habitat to get an appreciation of why the seeds do what they do.

When shed in Pretoria, the seed dries out and dies within hours. That’s because the seed shell has no water-holding ability whatsoever. In habitat the seed would have been shed in almost monsoonal rain and, if lucky, been flung between rocks by the breaking up of the falling fruit. Here it will be protected from predation long enough to germinate – which it does and completes in a handful of days.

Left: Mature pods just starting to open end February. Right: Pods are full of large and soft-shelled, oil-rich nuts. Photos by Jason Sampson

I’ve also learnt many lessons while working with these seeds.

For example, 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 what was happening.

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 aboveground parts of the young trees.

So in habitat, these seeds are optimised to “get underground” as fast as possible to escape being eaten, and the fires and drought that follow in winter.

Nature is amazing.

Above: The inner rim of the fruit bears short hairs which can be rather irritating when harvesting the nuts. Photo by @jpot123, iNaturalist

How to save and share seeds

Here’s a tip: Always propagate from the freshest seed possible. If harvesting nuts for propagation, it’s ideal to store them in plastic or a sealed container, but they will show signs of germination very soon, and should be planted in soil that is kept moist for the duration of the process. I have managed to delay germination by about a month by storing seed at 10 degrees Celsius, but they have no dormancy so that was probably about the maximum. Seed trays can be kept relatively dry over the plant’s first winter, and caudexes can be separated and potted up in spring.

I’ve never tried to propagate Sterculia murex from cuttings. It’s 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 the plant’s performance.

I have noticed some differences in performance both in habitat and cultivation, and recommend that you grow nuts from heavily bearing trees to get offspring with increased potential to bear well.

Get experimenting with Lowveld Chestnut

Admirably suited to a food forest, this striking tree may well have potential for commercialisation too. The nuts store very well when you freeze them, and cultivators with an experimental turn of mind may think about the potential for nut flours, nut milks and nut oils.

Remember to harvest the nuts as soon as possible from the moment the fruit opens. If you don’t, they could be predated upon by herbivorous animals and/or nut-eating birds – depending on where you live in South Africa!

For more information on this, or other orphan crops, please contact Jason Sampson at jason.sampson@up.ac.za