Chestnuts

Plant a chestnut tree today for decades of meaty, delicious nuts.

American chestnut trees are majestic. While young, the bark is a smooth, reddish-brown. As the tree matures, the bark becomes darker and deeply furrowed. Their mature height of over 100 feet equals 1/3rd of a football field. Try picturing that in your yard!

Ripe chestnuts (Couleur) Pixabay

Cousin to beeches and oaks, the roasted chestnuts of holiday fare fame should not be confused with horse chestnuts, which are mildly poisonous, or water chestnuts, which are aquatic tubers. No, chestnuts, or Sardian nuts, as they were called in their native Asia Minor, or Jupiter’s nuts, from the Roman Empire, have been cultivated since 2,000 B.C., and they have a rich, delicious history.

Chestnuts as food

Brought to Europe by Alexander the Great and the Roman Empire, chestnut trees thrive in the Mediterranean climate, providing a high carbohydrate food to the masses. Unlike most other nuts, chestnuts are not particularly high in protein or fat. Nutritionally, they are closer to grain or potatoes than nuts, containing 40% carbohydrates.

Chestnuts were a primary food source for much of southern Europe, until the potato was introduced. From the 1500s through the 1700s, Genoan landowners were required to plant four trees each year: olive, fig, mulberry, and chestnut. As a result, that area has rich, productive forests and farmland. [Imagine how productive your yard could be if you plant 4 food-producing trees each year!]

Being high in calories and carbohydrates, chestnuts were often ground into a flour to make a type of flatbread [chestnut flour does not rise, as it does not contain gluten]. Unfortunately, this earned it a reputation as a poor man’s food, which lead to a decline in interest. This was unfortunate, because chestnuts are a highly nutritious food.

Across the pond, Native Americans enjoyed local chestnut species long before Europeans arrived. Regions of the Appalachian Mountains were fully one-fourth chestnut trees. Since a mature American chestnut tree can produce 50 to 100 pounds of fruit each year, that ends up being a lot of food.

Epic chestnuts

There have been some impressive chestnut trees. The Tortworth Chestnut, also known as the Great Tree of Tortworth, found in South Gloucestershire, has been around since Stephen, King of England (1092-1154). This beast has a circumference of 50 feet! [If any of you have a photo of this tree, please share it in the Comments!] Even larger, the Hundred Horse Chestnut grows on Italy’s Mt. Etna and is believed to be the oldest living chestnut tree, at approximately 4,000 years.

Chestnut species

There are 8 or 9 different deciduous trees and shrubs that are called the chestnuts. These are placed into one of four groups: American, Chinese, European, and Japanese, for obvious reasons. Each species has distinct characteristics.

European and American chestnuts tend to grow more tree-like, with a single erect trunk, while the Asian varieties tend to be multilayered and more spread out. Also, the former varieties offer stunning fall foliage. There are hundreds of chestnut varieties to choose from. UC Davis offers an excellent list of chestnut trees suitable for growing in California.

Chestnut flowers

Like avocados, chestnuts have both male and female flowers. Chestnuts are not self-compatible, which means you will need at least two trees or shrubs to produce fruit. Flowers appear in late spring and early summer. Male (staminate) flowers are shaped like a cat’s tail and are called catkins. Catkins mature before the female flowers, and the pollen has a rich, sweet aroma. The female, fruit-producing (pistillate) flowers grow together in groups of 2 or 3, which end up forming a prickly, 4-lobed structure called a calybium. The calybium is what ultimately develops into the hull that protects the fruit. Pollen is moved predominantly by wind, though beneficial insects also perform some pollination.​​

Male chestnut flowers (Apple2000) CC BY-SA 3.0

Chestnut fruit

The fruit of chestnut trees is held in sharp, pokey burrs, called cupules. These burrs tend to be clustered. The burrs of some varieties each contain one nut, while other varieties can hold up to severn. Burrs turn yellowish-brown and split open as the fruit matures. Each fruit has a pointed end, called a flame, and an attachment scar end, called the hilum. Chestnut fruit has two skins: the hard outer pericarpus, called the heel, and an attached, thinner skin, called the pellicle or episperm. Chestnuts are both culinary and botanical nuts, unlike almonds, peanuts, cashews, and walnuts.

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Chestnut lumber

Chestnut lumber is lovely, but larger pieces tend to split. Most chestnut lumber is now produced through coppicing. Young chestnut lumber is more durable than oak of the same age. Both species contain high levels of tannins. Chestnut wood was a common source of natural tannins for tanning leather.

Chestnut branch (Vassil) Public Domain

How to grow chestnuts

Chestnuts are in high demand and the supply is limited. This keeps prices high, and is a good argument for growing your own (assuming you are not in a hurry). Going from bare root sapling to mature, productive tree takes about 10 years. Chestnuts need specific chilling hours to produce flowers and fruit. If the dormant period does not get cold enough, you will still have a beautiful tree, but no homegrown chestnuts. Also, if two chestnut trees are planted such that their canopies touch, they produce no fruit. We don’t know why.

Allowed to fall to the ground, chestnut seeds germinate right away. You can start them in a cold frame, container, or seedbed outdoors, where they will experience winter temperatures. Seedlings require protection from squirrels and other rodents.

Chestnut trees prefer full sun. They need good drainage and regular irrigation (31 inches per year). Once established, chestnuts are drought resistant. They do not grow well in heavy clay or alkaline soil. Chestnuts prefer a soil pH of 5.5 to 6.0. If you live in the Bay Area, where alkaline clay is pretty much the rule, don’t despair. Chestnut scions can be grafted onto oak rootstock! Chestnut trees are managed much the way walnut trees are grown. Chestnut trees should be trained into a modified central leader scaffold system for the best sun exposure and overall health.

Chestnut pests and diseases

Squirrels, rabbits, deer, wild boar, livestock, and birds can all take a bite out of your chestnut harvest. You may want to consider a tree cage, at least while the tree is small. Chestnut gall wasps (in southeastern states), some moths, the oak roller weevil, oak aphid, filbert worm, oak leaf mining moth, shot hole borers, and the chestnut weevil are common pests of chestnut, depending on where you live.

In 1904, some Asian chestnut trees that had been planted on Long Island, were found to be infected with chestnut blight (Cryphonectria parasitica, formerly Eudothia parasitica). Over the next 40 years, 4 billion chestnut trees died, nearly wiping out the American chestnut. Reforestation efforts, started in the 1930s, using seeds from the few remaining living stumps are giving this majestic tree a new lease on life, but it’s a slow process. There are now blight-resistant cultivars. Chestnut trees are also susceptible to Armillaria rot. On the other hand, chestnuts are believed to be naturally resistant to oak rot fungus. You can protect your chestnut tree against sunburn by whitewashing the trunk, and help it stay healthy by mulching under the canopy (but not touching the trunk).

Roasting chestnuts

Chestnuts have been candied, soaked in wine, and roasted as a holiday tradition throughout Europe for a very long time. To early Christians, chestnuts symbolized chastity, while in modern day Japan, they symbolize both good times (mastery) and bad times (strength).

You can roast your own chestnuts at home in the oven. Start with raw, unpeeled, chestnuts. Cut an X on the rounded bottom of each nut. Some people soak their chestnuts in water for 30 to 60 minutes before baking, others use wine, and still others don’t soak at all. You decide. If you do soak them in water, drain and pat dry before roasting.

Spread the nuts out on a baking sheet. Bake for at least 15 to 20 minutes, or until the skins have pulled away from the cuts and the nutmeats have softened. Take them out of the oven and let the nuts rest for a few minutes. Peel and eat!

Did you know that chestnuts are the only nuts that contain vitamin C?

Now you know.