Where Do Walnuts Grow? Climate and Growing Zones

Walnuts grow in temperate climates with cold winters and long, warm summers – broadly USDA hardiness zones 5–9 for the English (Persian) walnut. A dormant tree survives about -25°C (-13°F), but open flowers and small nuts are damaged at about -1°C (30°F), so the best walnut sites are places where late spring frost does not settle, air drains freely, soil is at least 2 m (6.5 ft) deep and the water table stays below 2.5–3 m (8–10 ft). Choosing the right site matters more than the region: the wrong spot cannot be fixed later.

Where Walnuts Come From and Where They Are Grown

The English walnut originates from the mountains of Central Asia, the Caucasus and Anatolia, and has been grown across Persia and the Mediterranean for thousands of years – which is why it is also called the Persian walnut. Today the largest producers include China, the United States (California), Iran, Turkey and Chile, with significant production in Ukraine, Moldova, France, Romania and other parts of Europe, as well as Argentina and Australia. The black walnut is native to eastern North America.

Climate Requirements

• Winter hardiness: dormant trees to about -25°C (-13°F); Carpathian strains are hardier.
• Closed buds: tolerate about -3°C (27°F).
• Open flowers and small green nuts: damaged at about -1°C (30°F).
• Autumn shoots that have not hardened off: freeze at -9 to -12°C (16 to 10°F).
• Summer heat: above about 35°C (95°F), sun-exposed husks burn and kernels shrivel and darken.
• Altitude: grown from sea level to around 1,700 m (5,600 ft) in suitable latitudes.

Chilling Requirement

Walnuts need a period of winter cold to wake up properly in spring – measured as hours below 7°C (45°F). Depending on variety this ranges from about 500 to 2,000 hours; many common varieties need 500–1,000. Trees that do not get enough chill leaf out unevenly, flower over a long period and set fewer nuts, which is why walnuts struggle in very mild coastal and subtropical climates.

Late Spring Frost: The Biggest Risk

The largest crop losses come from late spring frost. A single frost night between bud swell and small-nut stage can destroy a year's crop. Frozen catkins release no pollen, and frozen female flowers set no nuts. Two ways to reduce the risk:

• Site: choose ground slightly higher than its surroundings, where cold air drains away.
• Variety: choose late-leafing varieties in frost-prone areas.

Summer Heat and Kernel Quality

Kernels need a long, warm summer to fill fully and stay light-coloured. In cool summers kernels may not fill the shell. Very hot, sunny conditions cause sunburn on the husk, which shrivels and darkens kernels; in severe years sunburn can cut the crop by up to half.

Slope, Aspect and Altitude

A difference of a few hundred metres – or just a slope versus a valley floor – can change frost risk dramatically.

• Cold air flows downhill on still nights, so slopes can be several degrees warmer than valley bottoms.
• Air movement on slopes dries leaves quickly, reducing anthracnose and walnut blight.
• Sun-facing slopes warm earlier in spring – which can mean earlier leafing and more frost exposure – so pair them with late-leafing varieties.

Soil and Water Table

Walnut roots go 2–4 m (6–13 ft) deep, and they drown when they reach the water table. On sites with a high water table, trees often grow well for a few years and then die back at 5–7 years old – one of the most expensive mistakes a grower can make.

• Dig a test pit to about 2 m (6.5 ft) and check for hardpan, rock and water.
• Look at how the ground behaves after heavy rain or snowmelt.
• Test the soil at several depths: ideal pH about 6–7, not heavy clay, not salty or very chalky.

Where Not to Plant Walnuts

• Valley floors and closed hollows where cold air pools.
• Flat, poorly drained land with a high water table.
• Soil less than about 2 m (6.5 ft) deep over rock or hardpan.
• Heavy, airless clay soils.
• Dry sites with no irrigation where summers are long and rainless.
• Very mild climates that cannot meet the chilling requirement.

Related Walnut Guides

• How to grow walnut trees: complete guide
• Best walnut tree varieties
• When to plant walnut trees
• Is a walnut orchard profitable?

Frequently Asked Questions

What climate do walnut trees need?

A temperate climate with cold winters (500–2,000 chill hours depending on variety), long warm summers and no late spring frost during flowering.

What USDA zones do walnut trees grow in?

English walnuts grow broadly in zones 5–9, Carpathian strains down to zone 5 or colder, and black walnut in zones 4–9.

Do walnut trees grow in the UK?

Yes. Late spring frosts and cool summers are the main limits, so late-leafing or UK-selected varieties such as Broadview and Buccaneer are preferred.

Can walnuts grow in hot climates?

Only where winters are cold enough for chilling. In hot summers, irrigation and protection from sunburn are essential.

Which countries grow the most walnuts?

China is the largest producer, followed by countries including the United States, Iran, Turkey and Chile.