Chestnut

Chestnuts have been grown by humans since about 2000 BCE and were carried by the armies of Alexander the Great as well as the later Roman armies. These armies planted chestnuts in their wake helping the European variety spread from its native Asia Minor to all over Europe.
Also known as Jupiter’s Nut, Sardian Nut, Husked Nut There are many species of chestnut. They grow all over the world including Europe, Asia and the Americas. Native lore about the chestnut generally refers to the chestnut that grows in the region the lore originated from, but they can and are often used interchangeably. See below for more detailed information on a selection of chestnut varieties.
Chestnut Varieties (This list is not exhaustive.)
American Chestnut, Castanea dentata Allegheny chinkapin, dwarf Chestnut, Castanea pumila Chinese Chestnut, Castanea mollissima European Chestnut, Sweet Chestnut, Spanish Chestnut Castanea sativa Japanese Chestnut, Castanea crenata
Similar, but unrelated plants include the Horse Chestnut and the Water Chestnut
History and Folklore Chestnuts have been grown by humans since about 2000 BCE and were carried by the armies of Alexander the Great as well as the later Roman armies. These armies planted chestnuts in their wake helping the European variety spread from its native Asia Minor to all over Europe.
Propagation Chestnut trees are excellent additions to wildlife and butterfly gardens. They provide nutritious food for a number of birds and small mammals as well as a number of different types of butterflies and moths.
Chestnut trees are very slow growing. They take 15 years to bear fruit and it can be 50 years before they bear significant fruit. They also do not bear fruit well alone and several must be grown in close proximity to one another for optimal fruit production. Chestnut trees enjoy well-drained soil and do well on hillsides and mountainsides.
Harvesting & Storage The fruit of the chestnut tree forms inside a prickly burr that turns brown when it is ready for harvesting, usually in late September through October over the course of several weeks. The burrs generally fall to the ground on their own and split open, making it relatively easy to remove the nuts from within, but sometimes they need a bit more coaxing. You can knock them down with a stick and pry the burrs open with a knife. This isn’t pleasant, as they are prickly.
Chestnuts can be smoked in a smokehouse to dry them for grinding into flour.
Magical Attributes Chestnuts carry masculine energy and resonate with the fire element and the planet Jupiter. The chestnut tree is associated with the God Zeus. Chestnuts can be eaten to encourage fertility and desire and may be carried as a charm by women who wish to conceive. Keeping chestnuts around the house (and eating them) encourages abundance.
Staves made from chestnut wood are said to encourage longevity, increase energy, enhance intuition and help with grounding and centering of energy. Chestnut wood can also be used to make talismans for justice, success, to gain the sympathy of your audience and to encourage your mind to take in information.
In Japan the chestnut fruit symbolizes both difficulties and overcoming them. They are eaten on New Year’s day for success and strength the coming year.
Early Christian folklore says that chestnuts symbolize chastity.
Healing Attributes Native Americans may have used a tisane of chestnut leaves to treat severe coughs and heart disease, a poultice of the leaves for sores and a decoction of the bark to treat worms.
Culinary Use Chestnuts were a staple food in Southern Europe, Turkey and parts of Asia where they thrived in areas where the rocky, thin soil made it impractical to grow grains. In these areas, chestnuts remain a popular food and you can buy roasted chestnuts from street vendors. Chestnuts are a remarkably versatile food that can take the place of grains and potatoes in the diet.
Since chestnuts ripen late in the year and store well into the cold months, they are a traditional addition to Midwinter and late winter celebrations.
Chestnuts can be roasted inside their peel, but you must cut the peel first to prevent bursting. The taste is sweet and nutty with a baked potato-like texture. You can roast them in the oven or over hot coals.
Chestnuts can also be peeled and deep-fried.
They are also dried and then ground into flour. This flour is then used to make breads and as a thickener for sauces. In Corsica it is used to make a fried doughnut-like pastry called fritelli. Polenta was once made out of this ingredient before corn was brought back from the new world. Chestnut flour does not rise as wheat flour does but the bread stays fresh for up to two weeks.
Chestnuts have the least fat and highest carbohydrates of the nuts and are rich in vitamin C, B vitamins, and a wide variety of minerals.
The chestnuts are a group of eight or nine species of deciduous trees and shrubs in the genus Castanea, in the beech family Fagaceae. They are native to temperate regions of the Northern Hemisphere. The name also refers to the edible nuts they produce.[1][2][3]
The unrelated horse chestnuts (genus Aesculus) are not true chestnuts but are named for producing nuts of similar appearance that are mildly poisonous to humans. They should not be confused with water chestnuts, which are tubers of an aquatic herbaceous plant in the sedge family Cyperaceae.[7][8] Other species commonly mistaken for chestnut trees are the chestnut oak (Quercus prinus) and the American beech (Fagus grandifolia),[9][10] both of which are also in the Fagaceae. Etymology
Female chestnut flowers
Male chestnut flowers The name "chestnut" is derived from an earlier English term "chesten nut", which descends from the Old French word chastain (Modern French, châtaigne).[11] The French word in turn derives from Latin Castanea (also the scientific name of the tree), which traces to the Ancient Greek word κάστανον (sweet chestnut).[12] A possible source of the Greek word is the ancient town of Kastanea in Thessaly.[5] The town probably took its name, though, from the trees growing around it.[13] In the Mediterranean climate zone, chestnut trees are rarer in Greece because the chalky soil is not conducive to the tree's growth. Kastania is located on one of the relatively few sedimentary or siliceous outcrops. They grow so abundantly there that their presence would have determined the place's name.[14] Still others take the name as coming from the Greek name of Sardis glans (Sardis acorn) – Sardis being the capital of Lydia, Asia Minor, from where the fruit had spread.[15]
The name is cited twice in the King James Version of the Bible. In one instance, Jacob puts peeled twigs in the water troughs to promote healthy offspring of his livestock.[16] Although it may indicate another tree, it indicates the fruit was a local staple food in the early 17th century.[13]
These synonyms are or have been in use: Fagus Castanea (used by Linnaeus in first edition of Species Plantarum, 1753),[17] Sardian nut, Jupiter's nut, husked nut, and Spanish chestnut (U.S.).[18]
Description Chestnut trees are of moderate growth rate (for the Chinese chestnut tree) to fast-growing for American and European species.[18] Their mature heights vary from the smallest species of chinkapins, often shrubby,[19] to the giant of past American forests, C. dentata that could reach 60 m. Between these extremes are found the Japanese chestnut (C. crenata) at 10 m average;[note 1] followed by the Chinese chestnut (C. mollissima) at about 15 m, then the European chestnut (C. sativa) around 30 m.[10]
The Chinese and more so the Japanese chestnuts are both often multileadered and wide-spreading,[10] whereas European and especially American species tend to grow very erect when planted among others, with little tapering of their columnar trunks, which are firmly set and massive. When standing on their own, they spread on the sides and develop broad, rounded, dense crowns at maturity.[18] The latter two's foliage has striking yellow autumn coloring.[21]

Bark - sweet chestnut (C. sativa) Its bark is smooth when young,[22] of a vinous maroon or red-brown color for the American chestnut,[13] grey for the European chestnut. With age, American species' bark becomes grey and darker, thick, and deeply furrowed; the furrows run longitudinally, and tend to twist around the trunk as the tree ages; it sometimes reminds one of a large cable with twisted strands.[18]

C. sativa male catkins (pale buff) and female catkins (green, spiny, partly hidden by leaves) The leaves are simple, ovate or lanceolate, 10–30 cm long and 4–10 cm wide, with sharply pointed, widely spaced teeth, with shallow rounded sinuates between.[7]
The flowers follow the leaves, appearing in late spring or early summer[18] or into July.[19] They are arranged in long catkins of two kinds,[19] with both kinds being borne on every tree.[13] Some catkins are made of only male flowers, which mature first. Each flower has eight stamens, or 10 to 12 for C. mollissima.[23] The ripe pollen carries a heavy, sweet odor[19] that some people find too sweet or unpleasant. Other catkins have these pollen-bearing flowers, but also carry near the twig from which these spring, small clusters of female or fruit-producing flowers. Two or three flowers together form a four-lobed prickly calybium, which ultimately grows completely together to make the brown hull, or husk, covering the fruits.[18]

Chestnuts can be found on the ground around trees Chestnut flowers are not self-compatible, so two trees are required for pollination. All Castanea species readily hybridize with each other.
The fruit is contained in a spiny (very sharp) cupule 5–11 cm in diameter, also called "bur" or "burr".[24] The burrs are often paired or clustered on the branch[19] and contain one to seven nuts according to the different species, varieties, and cultivars.[1][2][25][26] Around the time the fruits reach maturity, the burrs turn yellow-brown and split open in two or four sections. They can remain on the tree longer than they hold the fruit, but more often achieve complete opening and release the fruits only after having fallen on the ground; opening is partly due to soil humidity.[6]
The chestnut fruit has a pointed end with a small tuft at its tip (called "flame" in Italian[6]), and at the other end, a hilum – a pale brown attachment scar. In many varieties, the fruit is flattened on one or two sides. It has two skins. The first one is a hard, shiny, brown outer hull or husk, called the pericarpus;[27] the industry calls this the "peel".[6] Underneath the pericarpus is another, thinner skin, called the pellicle or episperm.[27] The pellicle closely adheres to the seed itself, following the grooves usually present at the surface of the fruit. These grooves are of variable sizes and depths according to the species and variety.
The fruit inside these shows two cotyledons with a creamy-white flesh throughout,[8] except in some varieties which show only one cotyledon, and whose episperm is only slightly or not intruded at all. Usually, these varieties have only one large fruit per burr, well rounded (no flat face) and which is called "marron"[6] (marron de Lyon in France, marron di Mugello in Italy, or paragon).
Chestnut fruit has no epigeal dormancy and germinate right upon falling to the ground in the autumn, with the roots emerging from the seed right away and the leaves and stem the following spring. Because the seeds lack a coating or internal food supply, they lose viability soon after ripening and must be planted immediately.
The superior fruiting varieties among European chestnuts have good size, sweet taste, and easy-to-remove inner skins.[28][29] American chestnuts are usually very small (around 5 g), but sweet-tasting with easy-to-remove pellicles. Some Japanese varieties have very large nuts (around 40 g), with typically difficult-to-remove pellicles. Chinese chestnut pellicles are usually easy to remove, and their sizes vary greatly according to the varieties, although usually smaller than the Japanese chestnut.[10]
It has been a staple food in southern Europe, Turkey, and southwestern and eastern Asia[8][34] for millennia, largely replacing cereals where these would not grow well, if at all, in mountainous Mediterranean areas.[35] Evidence of its cultivation by man is found since around 2000 BC.[36] Alexander the Great and the Romans planted chestnut trees across Europe while on their various campaigns. A Greek army is said to have survived their retreat from Asia Minor in 401–399 BC thanks to their stores of chestnuts.[37] Ancient Greeks, such as Dioscorides and Galen, wrote of chestnuts to comment on their medicinal properties—and of the flatulence induced by eating too much of it.[14] To the early Christians, chestnuts symbolized chastity.[16] Until the introduction of the potato, whole forest-dwelling communities which had scarce access to wheat flour relied on chestnuts as their main source of carbohydrates.[8] In some parts of Italy, a cake made of chestnuts is used as a substitute for potatoes.[5] In 1583, Charles Estienne and Jean Liébault wrote, "an infinity of people live on nothing else but (the chestnut)".[38] In 1802, an Italian agronomist said of Tuscany that "the fruit of the chestnut tree is practically the sole subsistence of our highlanders",[39] while in 1879 it was said that it almost exclusively fed whole populations for half the year, as "a temporary but complete substitution for cereals".[40] Boundary records compiled in the reign of John already showed the famous Tortworth Chestnut in South Gloucestershire, as a landmark; it was also known by the same name of "Great Chestnut of Tortworth" in the days of Stephen. This tree measured over 50 feet (15 m) in circumference at 5 feet (1.5 m) from the ground in 1720. The Hundred Horse Chestnut in the chestnut forests on Mount Etna is the oldest living chestnut tree and is said to be even larger. Chestnut trees particularly flourish in the Mediterranean basin.[18] In 1584, the governor of Genoa, which dominated Corsica, ordered all the farmers and landowners to plant four trees yearly, among which was a chestnut tree – plus olive, fig and mulberry trees. Many communities owe their origin and former richness to the ensuing chestnut woods.[41] In France, the marron glacé, a candied chestnut involving 16 different processes in a typically French cooking style, is always served at Christmas and New Year's time.[16] In Modena, Italy, they are soaked in wine before roasting and serving,[16] and are also traditionally eaten on Saint Simon's Day in Tuscany.[37] In the Romagna region, roasted chestnuts are often served with a traditional wine, the Cagnina di Romagna. It is traditional to eat roasted chestnuts in Portugal on St. Martin's Day.
Their popularity declined during the last few centuries, partly due to their reputation of "food for poor people".[42] Many people did not want to take chestnut bread as "bread" because chestnut flour does not rise. Some slandered chestnut products in such words as the bread which "gives a sallow complexion" written in 1770,[43] or in 1841 "this kind of mortar which is called a soup".[44] The last decades' worldwide renewal may have profited from the huge reforestation efforts started in the 1930s in the United States to establish varieties of C. sativa which may be resistant to chestnut blight, as well as to relieve the strain on cereal supplies.

Chestnut output in 2005 The main region in Italy for chestnut production is the Mugello region; in 1996, the European Community granted the fruit Protected Geographic Indication (equivalent to the French Appellation d'Origine Contrôlée) status to the Mugello sweet chestnut. It is markedly sweet, peels easily, is not excessively floury or astringent, and has notes of vanilla, hazelnut, and, more subtly, fresh bread. There is no unpleasant aroma, such as yeast, fungus, mold or paper, which sometimes occur with other chestnuts.[45] The main regions in France for chestnut production are the départements of Ardèche, with the famous "Châtaigne d'Ardèche" (A.O.C), of the Var (Eastern Provence), of the Cévennes (Gard and Lozère départements) and of the Lyon region. France annually produces over 1,000 metric tons, but still imports about 8,000 metric tons, mainly from Italy.[46]
In Portugal's archipelago of Madeira, chestnut liquor is a traditional beverage, and it is gaining popularity with the tourists and in continental Portugal.[47]
Asia Always served as part of the New Year's menu in Japan, chestnuts represent both success and hard times—mastery and strength.[16] The Japanese chestnut (kuri) was in cultivation before rice[48] and the Chinese chestnut (C. mollissima) possibly for 2,000 to 6,000 years.[10]
During British colonial rule in the mid-1700s to 1947, the sweet chestnut (C. sativa) was widely introduced in the temperate parts of the Indian subcontinent, mainly in the lower- to middle Himalayas. They are widely found in British-founded hill stations in northern India, and to a lesser extent in Bhutan and Nepal. They are mainly used as an ornamental tree and are found in almost all British-founded botanical gardens and official governmental compounds (such as larger official residences) in temperate parts of the Indian subcontinent.
China has about 300 chestnut cultivars. Moreover, the 'Dandong' chestnut (belonging to the Japanese chestnut C. crenata) is a major cultivar in Liaoning Province.[49]
North America American Indians were eating the American chestnut species, mainly C. dentata and some others, long before European immigrants introduced their stock to America, and before the arrival of chestnut blight.[37] In some places, such as the Appalachian Mountains, one-quarter of hardwoods were chestnuts. Mature trees often grew straight and branch-free for 50 feet (15 m), up to 100 feet, averaging up to 5 ft in diameter. For three centuries, most barns and homes east of the Mississippi River were made from it.[50] In 1911, the food book The Grocer's Encyclopedia noted that a cannery in Holland included in its "vegetables-and-meat" ready-cooked combinations, a "chestnuts and sausages" casserole besides the more classic "beef and onions" and "green peas and veal". This celebrated the chestnut culture that would bring whole villages out in the woods for three weeks each autumn (and keep them busy all winter), and deplored the lack of food diversity in the United States's shop shelves.[5]
Soon after that, though, the American chestnuts were nearly wiped out by chestnut blight. The discovery of the blight fungus on some Asian chestnut trees planted on Long Island, New York, was made public in 1904. Within 40 years, the nearly four billion-strong American chestnut population in North America was devastated;[51] only a few clumps of trees remained in Michigan, Wisconsin, California and the Pacific Northwest.[37] Due to disease, American chestnut wood almost disappeared from the market for decades, although quantities can still be obtained as reclaimed lumber.[52] Today, they only survive as single trees separated from any others (very rare), and as living stumps, or "stools", with only a few growing enough shoots to produce seeds shortly before dying. This is just enough to preserve the genetic material used to engineer an American chestnut tree with the minimal necessary genetic input from any of the disease-immune Asiatic species. Efforts started in the 1930s are still ongoing to repopulate the country with these trees, in Massachusetts[53] and many places elsewhere in the United States.[54] In the 1970s, geneticist Charles Burnham began back-breeding Asian chestnut into American chestnut populations to confer blight resistance with the minimum difference in genes.[55] In the 1950s, the Dunstan chestnut was developed in Greensboro, N.C., and constitutes the majority of blight-free chestnuts produced in the United States annually.
Today, the nut's demand outstrips supply. The United States imported 4,056 metric tons of European in-shell chestnuts worth $10 million in 2007.[56] The U.S. chestnut industry is in its infancy, producing less than 1% of total world production. Since the mid-20th century, most of the US imports are from Southern Italy, with the large, meaty, and richly flavored Sicilian chestnuts being considered among the best quality for bulk sale and supermarket retail. Some imports come from Portugal and France. The next two largest sources of imports are China and South Korea.[56] The French varieties of marrons are highly favored and sold at high prices in gourmet shops.[16]
A study of the sector in 2005 found that US producers are mainly part-timers diversifying an existing agricultural business, or hobbyists.[57] Another recent study indicates that investment in a new plantation takes 13 years to break even, at least within the current Australian market.[58] Starting a small-scale operation requires a relatively low initial investment; this is a factor in the small size of the present production operations, with half of them being between 3 and 10 acres (12,000 and 40,000 m2). Another determining factor in the small productivity of the sector is that most orchards have been created less than 10 years ago, so have young trees which are as now barely entering commercial production.[57] Assuming a 10 kg (22 lb) yield for a 10-year-old tree is a reliable conservative estimate, though some exceptional specimens of that age have yielded 100 kg (220 lb).[58] So, most producers earn less than $5,000 per year, with a third of them not having sold anything so far.[57]
Moreover, the plantings have so far been mostly of Chinese species, but the products are not readily available.[57] The American Chestnut Foundation currently recommends waiting a while more before large-scale planting,[citation needed] because the organization and its associates (the American Chestnut Cooperators' Foundation and many others from education, research and industry sectors contributing to the program) are in the last stages of developing a variety that is as close as possible to the American chestnut, while having incorporated the blight-resistant gene of the Asiatic species. Considering the additional advantage that chestnut trees can be easily grown organically,[57] and assuming the development of brands in the market and everything else being equal, home-grown products would reach higher prices than imports,[citation needed] the high volume of which indicates a market with expanding prospects.[57] As of 2008, the price for chestnuts sold fresh in the shell ranges from $1.50/lb ($3.30/kg) wholesale to about $5/lb ($11/kg) retail, depending mainly on the size.[56][57]
Australia, New Zealand The Australian gold rush of the 1850s and 1860s led to the first recorded plantings of European chestnut trees, brought from Europe by settlers.[10] Along the years, most chestnut tree plantations were C. sativa stock, which is still the dominant species. Some of these remain today. Some trees in northern Victoria are around 120 years old and up to 60 m tall. Chestnuts grow well in southwest Western Australia, which has cold winters and warm to hot summers.[8] As of 2008, the country has nearly 350 growers, annually producing around 1,200 metric tons of chestnuts, of which 80% come from northeast Victoria. The produce is mostly sold to the domestic fresh fruit market. Chestnuts are slowly gaining popularity in Australia. A considerable increase in production is expected in the next 10 years, due to the increase in commercial plantings during the last 15[4] to 25 years.[8] By far, the most common species in Australia is the European chestnut, but small numbers of the other species, as well as some hybrids have been planted.[4] The Japanese chestnut (C. crenata) does well in wet and humid weather and in hot summers (about 30 °C and was introduced to New Zealand in the early 1900s, more so in the upper North Island region.[10]
Nutrition Chestnuts (raw, peeled) Nutritional value per 100 g (3.5 oz) Energy 820 kJ (200 kcal) Carbohydrates 44 g Sugars 11 g Fat 1.3 g Protein 1.6 g Vitamins Quantity%DV† Vitamin A equiv. 0%1 μg Thiamine (B1) 13%0.144 mg Riboflavin (B2) 1%0.016 mg Niacin (B3) 7%1.102 mg Vitamin B6 27%0.352 mg Folate (B9) 15%58 μg Vitamin B12 0%0 μg Vitamin C 48%40.2 mg Minerals Quantity%DV† Calcium 2%19 mg Copper 21%0.42 mg Iron 7%0.94 mg Magnesium 8%30 mg Manganese 16%0.34 mg Phosphorus 5%38 mg Potassium 10%484 mg Sodium 0%2 mg Zinc 5%0.49 mg Other constituents Quantity Water 60.21 g Units μg = micrograms • mg = milligrams IU = International units †Percentages are roughly approximated using US recommendations for adults. Source: USDA FoodData Central Chestnuts depart from the norm for culinary nuts, as they have little protein or fat; their calories come chiefly from carbohydrates. Fresh chestnut fruits provide about 800 kJ (190 kcal) of food energy per 100 g of edible parts, which is much lower than walnuts, almonds, other nuts, and dried fruit (about 2,500 kJ or 600 kcal per 100 g).[45] Chestnuts contain very little fat, mostly unsaturated, and no gluten.[10]
Their carbohydrate content compares with that of wheat[42] and rice. Chestnuts have twice as much starch as the potato on an as-is basis.[37] They contain about 8% of various sugars, mainly sucrose, glucose, fructose, and in lesser amounts, stachyose and raffinose, which are fermented in the lower gut, producing gas.[6] In some areas, sweet chestnut trees are called "bread trees".[45][59] When chestnuts are just starting to ripen, the fruit are mostly starch and are very firm under finger pressure from the high water content. As the chestnuts ripen, the starch is slowly converted into sugars, and moisture content decreases. Upon pressing the chestnut, a slight 'give' can be felt; the hull is not so tense, and space occurs between it and the flesh of the fruit.[60] They are the only "nuts" that contain vitamin C, with about 40 mg per 100 g of raw product, about 65% of the US recommended daily intake. The amount of vitamin C decreases by about 40% after heating. Fresh chestnuts contain about 52% water by weight, which evaporates relatively quickly during storage. They can lose as much as 1% of weight in one day at 20 °C (68 °F) and 70% relative humidity.[6]
Tannin is contained in the bark[61][62] as well as in the wood, leaves, and seed husks. The husks contain 10–13% tannin.[62]
The nuts of Castanea alnifolia are primarily eaten by wildlife.[63]
Cultivation, pests, and diseases
Chestnuts Climate, seasonal germination cycle Chestnuts produce a better crop when subjected to chill temperatures during the dormant period. Frosts and snowfalls are beneficial rather than harmful to the trees.[8][58] The dormant plant is very cold-hardy in Britain,[64] to the Royal Horticultural Society's H6 hardiness rating, to -20 °C.[65] Chestnut is hardy to USDA zone 5, which is −29 °C (−20 °F) lower in average minimal temperature than London in zone 9.[66] The young growth in spring, even on mature plants, though, is frost-tender;[64][66] bud-burst is later than most other fruit trees, so late frosts can be damaging to young buds.[58]
Trees can be found at altitudes between 200 and 1000 m above sea level;[58] some mention between 300 and 750 m altitude,[67] while the famous Hundred Horse Chestnut on Mount Etna stands at 1200 metres.[68] They can tolerate maritime exposure, although growth is reduced.[66]
Seeds germinate in late winter or early spring,[64][66] but the life length is short. If kept moist, they can be stored in a cool place for a few months, but must be checked regularly for signs of germination.[66] Low temperature prolongs dormancy.[6] Sowing them as soon as ripe is better, either in cold frames or seedbeds outdoors,[69] where they can be left in situ for 1 to 2 years before being planted in their permanent positions,[66] or in pots, where the plants can be put out into their permanent positions in summer or autumn. They must be protected from the cold in their first winter,[64] and also from mice and squirrels.[66]
Chestnuts are considered self-sterile,[66][70] so at least two trees are needed for pollination.[60]
Soil requirements Castanea grows best in a soil with good drainage and adequate moisture.[58][60] The tree prefers sloping, deep soils; it does not like shallow or heavy soils with impermeable, clay subsoils.[58] The Chinese chestnut prefers a fertile, well-drained soil, but it grows well in fairly dry, rocky, or poor soils.[71]
Although Castanea can grow in very acid soil,[66] and while these soils are reasonably well tolerated, the preferred range is from pH 5.5-6.0.[58] It does not grow well on alkaline soils, such as chalk,[12][66] but thrives on soils such as those derived from granite, sandstone, or schist.[12] On alkaline soils, chestnut trees can be grown by grafting them onto oak rootstocks.[52] Recently cleared land is best avoided to help resist the root rot, Armillaria mellia.[58]
Sun exposure Castanea likes a full sun position.[60] An experiment with C. dentata seedlings in Ohio confirmed the need for sun for optimal growth.[72] The butt of the tree is sometimes painted with white paint to protect the tree from sunburn until it has developed enough canopy.[58] Wide spacing between the trees encourages low, broad crowns with maximum exposure to sunshine to increase fruit production. Where chestnut trees touch, virtually no fruit is produced. Current industrial planting spacings can range from 7 x 7 to 20 x 20 m. The closer plantings, which are more popular, mean quicker increases in short-term production, but heavy pruning or even tree removal is required later.[58]
Watering The optimum rainfall for chestnut trees is 800 mm (31 in) or more, ideally in even distribution throughout the year. Mulching during summer is recommended. Rainfall below 700 mm (28 in) per year needs be complemented with, for example, a drip irrigation system. This should water the soil at the outer half of the circle formed by the drip line[58] to encourage root growth.
Independently from annual rainfall, watering young trees is recommended at least during summer and early autumn.[58] Once established, they resist droughts well.[12][26][73][74]
Preservation In addition to being consumed fresh, chestnuts can also be canned, pureed, or preserved in sugar or syrup (marrons glacés). Shelled and cooked nuts should be covered, refrigerated, and used within 3–4 days. Cooked chestnuts, either whole, chopped, or pureed, may be frozen in an airtight container and held up to 9 months. Because of their high water content, transpiration rates, and consequent loss weight, the nuts react as fresh fruits (not as nuts). They should be kept cool at all times, including in shops when on display for sale.[58] To preserve their freshness for a few months with no artificial refrigeration, the chestnuts can be soaked in cold water for about 20 hours immediately after harvest, after which they are dried in the shade, then layered in dry sand.[42] Chestnuts behave similarly to seeds in that they produce very little ethylene, and their respiration rate is low, varying between 5 and 20 mg/(kg·h) depending on the temperature.[6]