Castanea

Serrated leaves, twisted bark and tasty nuts make the sweet chestnut a highly prized tree, writes Miranda Kimberley.

C. sativa chestnuts - image: Floramedia
C. sativa chestnuts - image: Floramedia

Just like oak and beech, the sweet chestnut is an iconic tree in British woodlands, particularly in the south, where they thrive on the lighter soils, and have been used for coppicing and producing poles and nuts. Though not considered a native tree, they have been part of our landscape for centuries and are said to have been planted in great number by the Romans. Serrated leaves, twisted bark and tasty nuts, so good for roasting, make them highly prized.

Part of the beech family, Fagaceae, there are 12 species of Castanea. They are deciduous trees and shrubs found in northern hemisphere countries with temperate climates. All of them have serrated leaves and they produce yellowy catkins that are not conspicuous but when flowering en masse across the canopy they can be very striking.

Without doubt the European or Spanish sweet chestnut, C. sativa, is our best-loved species of the genus. A grand dame of our woodlands, it is regarded as an honorary native. It was very popular in the 18th and 19th centuries so historic specimens can be found in parklands and on large estates. Large areas of woodland are still dedicated to commercial coppicing in Kent and Sussex. With the decreasing health of horse chestnut trees, C. sativa is recommended as a good alternative for planting grand avenues.

Other species of Castanea are not widely seen in cultivation. The Japanese chestnut, C. crenata, is a smaller tree, or sometimes a large shrub, that produces nuts that are longer and narrower than those of
C. sativa.

French breeders have been doing a lot of work hybridising the Japanese and European chestnut over the past 40 years and the result is many varieties that produce heavy crops of large, fine-tasting nuts. The nuts of these French varieties are apparently easier to peel and the trees are resistant to the chestnut weevil and to chestnut blight.

Specialist grower Martin Crawford recommends C. sativa ‘Bournette’ as one of the best trees to choose should you be planting for nut production.

The Chinese sweet chestnut, C. henryi, is again a much smaller tree and has leaves with a paler green underside. A specimen planted around 45 years ago at Kew Gardens is said to have only reached 5m so far, though in the wild it would become a much larger tree.

Castanea are long-lived, drought resistant trees. They prefer well-drained, neutral-to-acid, light soil. Being moderately lime-tolerant, they can be grown over chalk if the soil is deep enough, but they will become chlorotic on shallow, chalky soils.

Unfortunately, there is a serious disease in mainland Europe that affects sweet chestnut trees, called chestnut blight, though it is not currently known to be present in the UK. Caused by the ascomycete fungus Cryphonectria parasitica, it wiped out vast forests of American sweet chestnut (C. dentata) in North America, killing 3.5 billion trees, in the first half of the 20th century.

It has been present in mainland Europe since the 1930s and has spread steadily since then, affecting C. sativa and leading to significant trees losses, although not to the same extent as in the USA.

In 2011 it was found for the first time in the UK on trees planted in Warwickshire and East Sussex that were imported from the same source. The infected trees were dug up and burned, and the UK is now considered free of chestnut blight.

There are now restrictions on importing trees from areas in Europe known to be infected with Cryphonectria parasitica. As a result there are low stocks of Castanea available in the UK. Specialist nurseries such as Agroforestry Research Trust in Devon sell several varieties and larger nurseries such as Frank P Matthews in Herefordshire are building up their own UK-grown stock, but they will not be available for a few years yet.

What the specialists say

Martin Crawford, director, Agroforestry Research Trust, Devon

"Castanea are generally very healthy nut trees that can be highly productive if the right selections
are planted, and then they have good commercial potential. The species or varieties that stand out
for me include C. sativa ‘Belle Epine’ and ‘Marron de Goujounac’ as well as C. sativa × crenata ‘Bournette’, ‘Marigoule’, ‘Marlhac’, ‘Marsol’ and ‘Maridonne’.

"In France hybrid varieties (of European × Japanese) are mainly planted now for nut production. The varieties listed above are all excellent in our climate.

"Plant Castanea in acid and well-drained soil. In poorly drained soils they are susceptible to Phytophthora root diseases. Ideally plant them on a sheltered site so the pollen stays within the orchard (pollination happens via wind as well as bees and other insects).

"In mainland Europe chestnut blight is a serious and damaging disease. This is not present in the UK and there are strict import regulations about bringing in Castanea planting material."

Peter Chapman, managing director, Perryhill Nurseries, East Sussex

"We only stock a few varieties of Castanea and only in small numbers, due to the retail market being quite small for large-growing trees.

C. sativa ‘Anny’s Summer Red’ and ‘Albomarginata’ sell a few but we are unlikely to sell more than five a year, usually less. Restrictions apply for imports so we would source from UK growers."

In practice

Tony Kirkham, arboretum head, Royal Botanic Gardens, Kew

"Castanea is a great genus that could be used more, especially in the south. There are the potential threats to our tree stock of chestnut blight and the oriental chestnut gall wasp, both of which have recently been discovered in the UK and then eradicated.

"All the cultivars are strong growers but some of the variegated forms are prone to reversion so an eye must be kept on them. Good species include C. henryi, which is a small tree from China with dainty leaves, and C. mollissima from China that produces the best large fruits for roasting. C. crenata is a nice medium-sized tree from Japan. There are lots of good cultivars of C. sativa and the pure species is good.

"It’s a great timber tree and good for biodiversity habitats. They are easy to grow and transplant well. It needs strict formative training in the first years. Coppices well to make a make a multi-stemmed tree."

Species and cultivars

C. crenata, or the Japanese chestnut, is a spreading, medium-sized tree or large shrub. Its nuts are longer and narrower than European chestnuts, and encased in spiny burrs. Hardy to -25°C. Height: 10m.

C. dentata, the American sweet chestnut, sadly no longer forms woodlands across the eastern USA since being devastated by blight and is very rarely seen in cultivation. It is a broad, rounded deciduous tree that differs from European sweet chestnut with its narrower, glabrous leaves. Breeding has introduced resistance genes from Japanese and Chinese chestnuts into moderately resistant dentata strains.

C. henryi is a Chinese species that can become a 20m-tall tree in its native habitat but usually forms a distinct shrub if grown in the UK. Has oblong-lanceolate leaves that are green but rather paler below and quite glabrous. Height: 5m.

C. mollissima, the Chinese chestnut, is a small, rounded, blight-resistant tree that produces easy-peeling sweet nuts.

C. sativa, the European chestnut, is a large tree grown in woodlands, parklands and estates. Produces medium to large nuts. Commercially planted for timber and coppicing of poles for fencing. Susceptible to blight. Height: 30-35m.
C. sativa ‘Albomarginata’ Award of Garden Merit (H6) is a vigorous tree with long serrated leaves that have creamy white margins. Also features pale-yellow catkins in early summer. Height: up to 20m. Spread: 15m.
C. sativa ‘Maravel’ is a rare majestic tree suitable for larger gardens and woodland. Produces creamy white flower spikes in midsummer and large crops of light-brown edible sweet chestnuts. Height: 25m. Spread: 20m.
C. sativa × crenata ‘Bournette’ is one of the best of the French varieties produced by crossing the Japanese and European sweet chestnuts. It produces heavy crops of fine tasting nuts. Height: 8-10m. Spread: 12m after 20 years.

Thank you to Floramedia, which supplied the images for this article from its photo library
www.floramedia-picture-library.com


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