If you depend on where the chestnuts are going to be, and where the deer are, you have to be attuned to the outside world. - Howard Rheingold, American writer and critic.


This month we’re looking at another sizeable but productive tree, best suited to larger sections or lifestyle blocks. It’s one of the less mainstream, but equally useful nuts, the chestnut. A stalwart of European and Asian street vendors in winter, roasted chestnuts are a popular pavement snack, and they certainly have their devotees, not least amongst those returning from overseas sojourns. The starchy, potato-esque nuts can be a trifle tricky to prepare but are a boon for those on restrictive diets as they make a nutritious, gluten-free flour substitute among other things.

The trees themselves are grow strongly, are long-lived and form large, handsome trees that make for great summer shade. The foliage is quite distinctive, even from a distance: large, shiny dark green leaves with a pronounced saw-tooth margin, echoing the prickly green husks that enclose the fruit. The popularity of chestnut trees in years past is plainly evident even here in the antipodes, where I often see avenues of them planted along the roadside on our State Highways, or clustered around old homesteads.

Chestnuts are fairly easy-care once established and can produce very heavy yields. If you’re looking for something to fill a big gap, provide shelter or shade as well as some spectacular autumn colour and a handy edible crop to boot, a chestnut tree might fit the bill. If roasting a few homegrown chestnuts on your log burner sounds like your idea of a great winter’s night in, take care to heed the age-old advice and cut a cross into the flat side of each nut first. My family learned the hard way with a few explosions as the result!

Roasting chestnuts

Chestnuts: a short family history

Not to be confused with the ornamental, smoother-husked horse chestnut (another great shade species and provider of much schoolyard entertainment in the form of conkers) or the Asian culinary stalwart, aquatic water chestnuts, true chestnuts are members of the Fagaceae or beech family and are related to many other great nut-producers including oaks and beeches.

The genus Castanea is an ancient one; well represented in the fossil records of 75 to 100 million years ago. Evidence exists of chestnuts being cultivated in the Mediterranean region for at least 3,000 years. Similarly, Chinese and Japanese chestnuts have been cultivated across China, Japan and Korea for possibly 2000-6000 years. In North America, indigenous chestnut species were keystone species in temperate original-growth forests until chestnut blight fungus arrived on the continent in the early 20th century and obliterated them. There are four main chestnut species:

The European chestnut, Castanea sativa, otherwise known as the sweet or Spanish chestnut. This is the most commonly found species in New Zealand and arrived here with the early settlers. Native to Turkey and the Black Sea region, it was spread widely across Europe in Roman times and remains commonplace. Nuts can vary considerably in size and quality between cultivars, but favourable types bear well and have large, sweet nuts which are easy to shell. Trees can reach 20-30 metres in height.

The Japanese chestnut, C. crenata has a shorter stature (reaching about 10 m in height) and has a more multi-stemmed, spreading growth habit. Japanese chestnut fruit can be quite large (up to 40 grams) but can be quite difficult to shell. All chestnuts have an outer shell (the brown, shiny, hardened layer) and a thinner, inner layer of skin known as the pellicle, which can cling tight to the nut and make preparation a little arduous. Japanese chestnuts, particularly, have an especially difficult-to-peel pellicle layer. On the upside, this species can cope with humid, wet climates and hot summers and as such may do well in Northland. They were brought into New Zealand in the early 1900s.

Chinese chestnuts, C. mollissima are medium-sized (reaching approximately 15 m in height), usually develop multiple leaders and have a similarly spreading growth habit to the Japanese types. The size of the nuts varies, typically smaller than those of the Japanese species, but generally having a good flavour, an easy-to-remove pellicle and yielding early. Chinese chestnuts are the species most resistant to chestnut blight.

American chestnuts, C. dentata are large, straight-trunked trees originally prized for their high-quality timber prior to the introduction of chestnut blight to the United States. The nuts are small but sweet and are easily shelled. It is the least-common species present in New Zealand.
These four species hybridise readily when grown in proximity and have done so with and without deliberate human intervention.

China is the world’s leading producer of chestnuts commercially, and New Zealand has a small but growing industry. Most Kiwi nuts are exported, with a small quantity sold fresh on the local market and increasing amounts being turned into processed, value-added products.

Chestnuts are not only useful for the production of nutritious nuts and useful timber, but also have a number of medicinal and other uses. The leaves and bark have astringent, anti-inflammatory and expectorant qualities and also have a high tannin content, making them useful for curing leather. When cut to ground level on a 10–12-year rotation, the trunks resprout readily, making them an excellent coppicing species for producing firewood, fence posts and railings. Chestnut leaves and skins have also been used to produce hair shampoo. After some prior preparation, often involving a soak in limewater, chestnuts have been added to animal feed; the foliage is also useful as fodder crop.

 

chestnut tree

Suitable climates and growing conditions

A temperate-climate crop, chestnuts do best in regions with warm summer temperatures for nut ripening (24°C or higher) and some winter chilling (in the region of 450-650 hours) for flower initiation. Late spring frosts can cause damage to young foliage in cooler regions, with -6°C conditions causing irreversible damage.

The main commercial growing regions in New Zealand were initially Waikato and the Bay of Plenty, later extending into Auckland, Hawkes Bay and Canterbury. As previously mentioned, the Japanese species may cope well with the warmer, more humid Northland climate. High summer temperatures aren’t an issue, and during the dormant winter phase, mature trees can survive temperatures down to -20°C.

Chestnut trees need room to grow, and as they have a deep taproot, don’t respond well to being transplanted, so choose your site carefully. Allow around 12-15 metres between trees if planting multiples (a minimum of two trees is advisable for cross-pollination and guaranteed fruit set). Chestnuts are long-lived trees, with many overseas reports of trees aged at hundreds, if not thousands of years – so don’t expect to have to replant at any time soon!

The trees are monoecious, with male and female flowers present on the same tree. Pollination is by wind, with assistance from insects. Chestnuts are partially self-fertile, but best planted in groups for consistent pollination. Without cross-pollination, nuts may form, but have empty or poorly filled shells.

The time it takes for young chestnut trees to come into production varies between species. Chinese chestnuts are the fastest to fruit and can produce a crop two to four years after planting. Hybrids also crop fairly soon, at four to five years of age, although nut quality can be variable and they often have a clingy pellicle, making preparation for culinary purposes onerous. In terms of yield, expect around 50 kg of nuts from trees 10-12 years of age, and up to 100 kg/tree at full maturity.

Chestnuts can be propagated from seed, and seedling production is necessary to provide rootstocks for grafting. Nuts collected in autumn can be stored over winter in cool (0°C), moist conditions and then sown in deep pots to germinate in spring.

Propagation is usually carried out using whip and tongue grafting or T- or chip-budding methods in spring. For good graft compatibility, it is advisable to graft the scions onto seedling rootstocks of the same cultivar. When cut, chestnut stems leak excessive amounts of sap, and this can hinder the formation of a graft union. Save yourself the trouble and purchase plants from a reputable nursery.

Site selection and planting

Chestnuts are best planted in the dormant winter season, May to August. Choose a site with a light, deep, well-drained soil, avoiding heavier clay types as the latter encourage root rots such as Phytophthora. They prefer an acidic soil pH and so can be planted with other acid-lovers such as conifers. A warm, sunny aspect will assist with flower production and although reasonably wind-tolerant, shelter when young is advisable.

Culture and care

Once established, chestnuts are a very easy-care species. Water and fertilise well at planting, and then ensure irrigation supply is adequate over the summer months, particularly in regions with low rainfall. The trees are not particularly hungry and can tolerate nutrient-poor soils but will produce best with a couple of applications of balanced general fertiliser at the start of spring and again midsummer. Allow 250-500 g per year of age for young trees, up to a total of 5 kg/tree at maturity, split into the two applications, applied in spring and summer. Don’t forget to spread this fertiliser before rainfall, or water it in well afterwards. Nitrogen, potassium and magnesium are nutrients of key importance.

Pruning

Being large trees, chestnuts need a good growth framework established in their formative years, so the tree structure is strong and able to withstand future stresses and strains. The central leader form is most commonly adopted. Remove any weak, damaged, or diseased branches and those that cross over each other in the initial stages. After this, little intervention is required.

Pests, diseases and what to do about them

Thankfully, New Zealand remains free of the debilitating chestnut diseases present in the Northern Hemisphere, such as the dreaded chestnut blight (Cryphonectria parasitica).

Phytophthora root rots can be exacerbated by heavy, wet soil types, so choose your planting site carefully and only purchase healthy, disease-free plants from reputable nurseries, as the infection can be brought in on the roots of new plants.

Late spring and early summer flights of the New Zealand native grass grub beetle, Costelytra zealandica can have a devastating defoliating effect on young chestnut foliage as the ravenous hoards feast on fresh new growth.

Rabbits, hares and possums can also wreak havoc, causing their fair share of damage to young trees, snapping branches, eating young bark and leaves, and in the case of possums, also feasting on the nuts at harvest. Try applying a liquid repellent such as Liquid Shotgun or Plantskydd.

Fungal diseases including Botrytis and Phomopsis spp. can infect developing nuts on the tree and cause postharvest rots on stored nuts.

Varieties: My top picks

Apart from un-named seedling varieties, many of the chestnut cultivars in New Zealand are known by numbers, the most popular being the Japanese/European hybrids 1105, 1015 and 1002.

1005 is the most popular. These are vigorous, strongly-branched, medium-sized trees producing heavy yields of large to very large nuts. They are ripe early, in March, before many of the other cultivars including 1015 (mid-season) and 1002 (late-season). The only downside to these hybrid varieties is that the pellicle can be difficult to remove – you may need to purchase a specialised chestnut peeler to make the task bearable.

If you have a particular interest in chestnut growing, you can join the New Zealand Chestnut Council.

 

Chestnuts on tree

What to do with your crop

Chestnuts should be harvested at regular intervals during the autumn ripening period – invest in a good pair of gloves to protect yourself from the spiny burrs, which of course need to be separated from the nuts themselves! Dry them well on wire racks before storing under refrigeration in ventilated (perforated) plastic bags. They will store well this way at 0-2°C and should keep for six months or more if carefully monitored.

The composition of chestnuts is greatly different than that of most other nuts. Fresh chestnuts contain approximately 50% water, contributing to their reasonably perishable nature. They are extremely low fat (1%), contain high levels of complex carbohydrates and around 5% protein. A boon for coeliacs and those following strict dietary regimes, the nuts are gluten and cholesterol free, low fat, low sodium, and are a source of vitamin C and potassium.

New Zealand’s chestnut industry research has, in the past, had a particular focus on value-added products. This has resulted in a veritable focus on the chestnut’s versatility: chestnut flour, bread, beer, juice, liqueur, jam, puree, ice cream, whole shelled nuts, shell-free chestnut crumb have all had their turn in the spotlight.

Chestnuts also play a number of culturally significant roles in the cuisines of many countries, including: being made into doughnut-like fritters in Italy, candied (marrons glacés) or sugared in French and Turkish cuisine, eaten on All Saints day in Spain and Portugal, and used to make iconic sweet desserts, including the Hungarian gesztenyepüré and the French ‘Mont Blanc’. Kuri gohan (chestnut rice) is a traditional Japanese aromatic rice dish served in autumn when chestnuts are in season and combines chestnuts with black sesame seeds and a pinch of salt.

A friend who grew up in country NSW recalls care packages containing dried chestnuts arriving courtesy of her maternal grandmother (Ah Pau) from Hong Kong. Her parents stewed these with pork, or made a clear soup using the chestnuts and pork or chicken broth – perhaps an acquired taste, but she says it was enjoyable.

Vendors selling stone-roasted chestnuts can be found on almost every street corner in Hong Kong in the autumn and my same friend has also spotted them on the streets of Kunming and Beijing. Want to recreate something similar at home? Try this fantastic method for producing tasty pan-roasted chestnuts with a butter-sugar glaze here, and while you’re visiting, check out the nifty ‘chestnut clips’ designed to firmly clamp your chestnuts while applying the all-essential cross-cut to the outer shell in preparation for safe cooking.

I’ll leave you with my most recent chestnut encounter…I prepared a fancy choux pastry dessert for dinner party guests, filled with a fancy chocolate and candied chestnut cream, for which I’d hoarded a tin of imported French crème de marrons (chestnut spread). It turned out pretty well, but unfortunately, I’m known for not labelling jars of ingredients in my pantry and I ended up sprinkling the first few portions of this masterpiece with what I thought was a light dusting of icing sugar. Turns out it was actually potato starch, and the first mouthfuls did not go down well! Better luck next time.

Disclaimer: the information supplied above is of a general nature and provided as reference material only. In regards to pest and disease control, please consult your agrichemical consultant for suitable products, application rates and further region-specific information.

Anna-Marie Barnes is an active member of the New Zealand Tree Crops Association who endeavours to grow and preserve as much of her own fresh produce as possible. When the weather’s no good for gardening, she can usually be found inside working on a batch of homemade cheese or soap.

The New Zealand Tree Crops Association is a voluntary organisation promoting interest in useful trees, such as those producing fruit, nuts, timber, fuel, wood, stock fodder, bee forage and other productive crops. Find out more about the NZTCA here: https://treecrops.org.nz/

Image Credits:

Roasting Chestnuts: Marc Pascuala from pixabay.com

Chestnuts on Tree: Christel from pixabay.com

Chestnuts: Pexels from pixabay.com

Chestnut Tree: Mona El Falakya from pixabay.com