Castanea sativa Seeds | Sweet Chestnut
LATIN NAME: Castanea sativa
COMMON NAME: Sweet Chestnut, European Chestnut
Plant Profile
The husk is a cupule studded with branching spines, green and hard through the summer and splitting open in autumn to drop one to three glossy brown nuts. The leaves are long and oblong with a coarsely toothed margin, each tooth drawn out into a bristle, and the male catkins are upright and heavily scented. Trees carry two sorts of catkin: wholly male ones in the leaf axils and mixed ones near the tip of the shoot, which is where the nuts set. Growers separate a marron, a large nut that fills its husk alone and comes away clean when peeled, from a châtaigne, one of several smaller nuts in a single husk, and the candied marrons and the finest flour are made from the first class.
Two pathogens wrote the modern history of the tree. The first, a soil-borne Phytophthora that causes ink disease, spread through the chestnut groves of southern Europe from the nineteenth century onwards, killing trees from the roots up and leaving a dark stain in the wood that gave the disease its name. The second was chestnut blight, which arrived with nursery stock in North America and all but eliminated the American chestnut over a few decades. Sweet chestnut is attacked by the same fungus but usually survives it, partly because it re-sprouts from the stool after the top is killed, and in Europe the blight is further weakened by a virus that reduces its virulence.
A third arrival changed European groves again. The chestnut gall wasp, native to China, was first recorded in Italy in 2002 and has since spread across the continent, laying its eggs in the buds so that the shoots carry clusters of green galls and set little fruit. The answer has been biological: the parasitoid Torymus sinensis, released alongside the pest, now follows the wasp through most of its new range.
A tree for nuts is grown as a standard on a clear trunk, with a wide crown and plenty of light; a wood for poles is grown as a stool cut every fifteen years or so. Either way the site should be deep, free-draining and lime-free, because sweet chestnut refuses chalk and hates waterlogged ground.
Science & Biotechnology
Chestnut wood and bark are among the richest natural sources of hydrolyzable tannins, in particular the ellagitannins castalagin and vescalagin, which is why chestnut extract became a mainstay of leather tanning in Italy and France and why the wood’s tannins also protect the timber outdoors. The nuts themselves are mostly starch with a good share of sugars, and the starch has an unusual property: chestnut flour holds water well and behaves differently from wheat, thickening a batter without gluten and going stale in a characteristic way.
Chestnut was among the first forest trees to be regenerated in the laboratory, with somatic embryos raised from immature cotyledons and from leaf tissue of selected trees. The technique is used to multiply material that combines marron quality with tolerance of ink disease and blight, and gene banks in Italy, France and Spain keep their old local varieties partly in vitro.
Uses & Benefits
On Corsica and in the Cévennes the chestnut was the flour crop, dried in smoke lofts and ground for polenta and for the flat cake made with olive oil and rosemary. Chestnut flour still goes into pancakes, biscuits and stuffing, and the nuts are candied whole as marrons glacés by the confectioners of Piedmont and Lyon. Chestnut honey, dark and slightly bitter, is harvested from the male catkins and is worth looking for where the trees are grown in quantity. The timber is split for fencing and stakes, and coppice poles are cut on a long rotation.
Growing from Seed
On the lower slopes of Mount Etna stands a sweet chestnut with a name drawn from a legend of a queen and a hundred mounted riders who sheltered beneath it in a storm. Its trunk has split into a ring of huge stems around a hollow centre, and it is regularly described as among the oldest trees in Europe. Age claims for such trees are hard to prove, but the shape is honest evidence of what sweet chestnut does better than almost any other European tree: when the trunk is damaged or falls, it throws up vigorous shoots from the stump and rebuilds itself. That capacity is the foundation of the chestnut economy, and it is also why the species survived the diseases that destroyed its American relative.
Choose heavy nuts that sink in water, and sow them in autumn about four centimetres deep in a deep pot of loam, leafmould and coarse grit. Mice will find them, so cover the pans with netting. The root goes down before the shoot comes up, and the seedlings lift a rosette of broad leaves within the first season; pot them on individually once the third true leaf has unfolded, and plant out with the root collar at soil level and a stout stake.
Keep the ground around a young tree clear of grass for the first few seasons and water only in a real drought, because the species is built for dry summers rather than wet ones. Nuts are attacked by a weevil that works inside the husk, and the infested ones float when the crop is washed, so grade the harvest in water before storing.
Our Take
Sweet chestnut earns its place as both a nut tree and a wood crop, and it is one of the few trees that pays you twice from the same stump. Pair it with a native cousin: the American chestnut for those planting for conservation, or the Chinese chestnut, which carries the best blight tolerance of the group. On the same acid loam the European beech makes a fine companion for a wood.
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