- Type
- Trees & Vines
- Difficulty
- Hard
- Season
- Fall
- Sowing
- Plant a sapling
Walnut
Juglans regia
Unsaturated fat and omega-3, in a nut that ripens in autumn
A walnut is the seed inside the fruit of the walnut tree. A green husk covers a hard shell, and cracking that shell gives you the wrinkled kernel people eat. The Donguibogam lists it under the fruit section, calling its nature neutral while noting a variant view that it is hot, and adds a caution that one should not eat much of it and should avoid it entirely in summer. The text also explains the name: it came from the lands to the north and west, and the green husk makes it look like a peach, hence hodo, the foreign peach. In a city you will meet it as whole nuts or shelled halves, and never as a tree on your balcony, since a mature walnut clears 20 m.
Year-Round Calendar
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Where It Grows
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Main producer
Accounts for more than half of world production. Yunnan, Shaanxi and Xinjiang are the main areas. Harvest September, October
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Main producer
California's Central Valley supplies effectively the entire crop, and a large share goes for export. Harvest September, October, November
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Major producer
Long-established growing areas run through the mountain villages of the Iranian Plateau. Harvest September, October
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Major producer
Grown along the Black Sea coast and on the inland plateau. Harvest September, October
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Major producer
As a Southern Hemisphere producer, it harvests half a year out of step with the Northern Hemisphere and sells into the off-season market. Harvest March, April, May
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Wild population
The world's largest surviving wild walnut forest stands around Arslanbob, on the south-western slopes of the Tian Shan. Harvest September, October
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Its native range is the mountain country stretching from Central Asia to the Iranian Plateau, which cannot be pinned to any single country, so no origin row has been set; only Kyrgyzstan, where wild populations survive, is listed as native. It spread east and west along the Silk Road, reaching the Korean Peninsula by way of China. With Chile in the Southern Hemisphere now added, new-crop walnuts arrive at points spread across the year.
- Optimum
- 15~25℃
- Range
- 0~35℃
- Hardiness
- Hardy
A temperate tree that needs a spell of cold each winter if its buds are to break evenly the following year. It tolerates winter cold itself, but late spring frosts damage the new shoots and blossom, and the nuts fill out best where summers are hot and dry and autumn brings little rain.
Harvested 5–7 years after planting. Even a grafted sapling takes five to seven years after planting before it begins to bear, and longer still before it yields a proper harvest. The month of planting and the month of harvest do not fall in the same year.
In Korea Central Korea and south
Gwangdeok in Cheonan, South Chungcheong, is the best-known growing area, and there are others in Gimcheon, North Gyeongsang, and Muju, North Jeolla. Valley bottoms, where late spring frost often settles, are avoided.
How to grow
- Light
- Open ground only. It needs at least six hours of direct sun in unenclosed soil, and it will not work in a pot.
- Soil and depth
- Open ground only. It wants deep, free-draining sandy loam at pH 6.0 to 7.0. The taproot drives straight down, so it never settles in container soil.
- Spacing
- Open ground only. Plant trees 8 to 10 m apart. Growing one in a pot is not realistic.
- Watering
- Water through summer droughts for the first two or three years after planting. Once established it mostly gets by on rainfall, but irrigate during a dry spell in July or August while the nuts are filling.
- Feeding
- Spread compost and a slow-release fertiliser in early spring before bud break, out along the drip line rather than against the trunk. Too much nitrogen thickens the shell and leaves the kernel thin.
- Harvest
- Pick in September and October, once the green husk splits. Strip the husk, wash the nuts, dry them in the sun for at least two days, then store somewhere cool with moving air. Wear gloves: husk juice stains hands and clothes brown.
What makes the difference. You cannot grow this in a pot, so learning to buy well is the practical skill. Shake a whole walnut; a rattle means the kernel has dried and shrunk, so leave it. Look for heavy nuts with no mould spotting on the shell. Shelled halves should be pale and come with little broken dust at the bottom of the bag. If the skin's astringency bothers you, blanch for 30 seconds and rub it off, then toast in a dry pan over low heat for three to four minutes to bring the aroma back.
Why this one is harder. A mature tree passes 20 m with a deep root system. Even a grafted tree takes five to seven years from planting before it sets nuts.
Common problems
- Peach pyralid moth You will see Holes in the husk with sawdust-like frass stuck around them, and a hollow nut inside What to do Time control to the June and August flights, and clear fallen damaged nuts the same day.
- Walnut leaf beetle You will see Leaves skeletonised down to the veins What to do Pick off affected leaves early, and if it spreads use a registered product aimed at the leaf undersides.
- Walnut anthracnose (brown leaf spot) You will see Brown blotches spreading over leaves and husks, with leaves dropping early What to do Rake up and remove fallen leaves to cut next year's inoculum, and thin branches so air moves through the canopy.
This page describes how a crop is grown and used. It does not claim health effects for any food, nor is it intended to prevent or treat disease. Component and study notes are references only and do not mean the same result occurs in people. Consult a medical professional about health concerns.
Health Benefits
What the Donguibogam recorded. Walnut appears in the Donguibogam's fruit section as hodo (胡桃). The text calls its nature neutral while carrying a variant note that it is hot, gives its taste as sweet with no toxicity, and cautions against eating much of it and against eating it at all in summer. It also records the preparation: soak the kernel in hot water and strip the thin skin off before use. The green outer husk is listed separately as a dye. This is a record from a seventeenth-century medical text, not a modern medical judgement.
Research on blood lipids. Observational studies and controlled feeding trials have repeatedly looked at nut intake, walnuts included, alongside blood lipid markers. Findings vary between studies, and none of this means walnuts prevent or treat any specific disease.
Old uses for husk and bark. The original text describes using the green outer husk to dye beard and hair black, and washing the hair with sap tapped from the tree. These are records of dyeing practices, not of anything eaten.
Nutrition
- Fat (About 65 g per 100 g) — Mostly unsaturated; high in calories
- Alpha-linolenic acid (ALA) (A plant omega-3) — High among nuts
- Protein (About 15 g per 100 g) — A plant protein source
- Polyphenols and ellagic acid (Concentrated in the papery inner skin) — The cause of the astringency and a common antioxidant marker
About 65% fat, mostly unsaturated Walnuts carry roughly 65 g of fat per 100 g, high even among nuts. Most of it is unsaturated, dominated by linoleic acid and alpha-linolenic acid. That puts the energy above 650 kcal per 100 g. A handful of about 30 g, which is seven or eight whole kernels, is the usual daily figure.
Alpha-linolenic acid (ALA) Walnuts sit near the top of the nut family for alpha-linolenic acid, the plant form of omega-3. It is not the same molecule as the EPA and DHA in oily fish, and the body converts only a fraction of it. That is why walnuts come up so often as an omega-3 source in diets light on fish.
The polyphenols live in the skin The thin brown skin wrapped around the kernel holds most of the polyphenols and ellagic acid. It is also the bitter part, so people peel it off, and a good share of the antioxidant content leaves with it. The Donguibogam says to soak the kernel in hot water and strip that thin skin before use, which shows old prescriptions removed it deliberately.
Magnesium, copper, manganese Walnuts carry a steady spread of trace minerals, notably magnesium, copper and manganese. Copper and manganese in particular cover a useful share of the daily reference intake in a single handful. They fill gaps that grain-heavy diets tend to leave open.
Pairings
○ Spinach, garlic chives, other green leaves — The fat in walnuts helps you take up the fat-soluble vitamins in leafy greens. Coarsely crushed walnut stirred through a seasoned green side dish adds a nutty note and changes the texture. Nuts in namul is a long-standing Korean habit, not a modern one. Korean Chive (Buchu / Garlic Chive) · Spinach
○ Anchovies and small bony fish — Stir-fried anchovies with walnuts is a familiar Korean side dish. Calcium from the fish and magnesium from the nut arrive together, and the nutty richness means you need less salt or soy to finish it.
○ Wholegrain bread and oatmeal — Eating walnuts alongside wholegrains at breakfast slows how fast the carbohydrate goes in. The chew adds to how long you feel full. Toasting the walnuts briefly first brings the aroma forward.
△ Tree nut allergy - a declarable allergen — Walnut is a declarable allergen, named on processed food labels by law. Anyone with a tree nut allergy does not eat it. A trace can trigger a severe reaction and can progress to anaphylaxis. Roasting and baking leave the allergenic proteins intact. Read the allergen line on the label first, and check the ingredients of breads, pastries and salads, where walnut travels easily. Start a child on a very small amount and watch the response, and where nut allergy runs in the family, seek medical advice before the first taste.
Varieties
- Persian walnut line (Sapling) — Most walnuts grown in Korea. The shell is comparatively thin.
- Manchurian walnut (Sapling) — A native Korean relative. Small nuts in a very hard shell.
- Black walnut (Sapling) — Thick shell and a strong aroma. Also used for timber.
- Grafted stock (Sapling) — Fruits two or three years sooner than a seedling. It still needs open ground.
Source: Donguibogam, Fruit Section (胡桃) · Rural Development Administration (nongsaro.go.kr)