Walnuts are edible seeds from trees of the genus Juglans, most commonly the English or Persian walnut (Juglans regia) and the Black walnut (Juglans nigra). Enclosed in a hard, wrinkled shell within a fleshy green husk, walnuts are prized for their rich, earthy flavour and outstanding nutritional profile.

The edible kernel consists of two lobes and is exceptionally high in healthy fats — particularly omega-3 fatty acids — as well as protein, dietary fibre, vitamin E, magnesium, and phosphorus. Regular consumption is associated with benefits for heart health, cognitive function, and the reduction of inflammation.

Walnuts can be eaten raw, toasted, or used in a wide range of culinary applications including salads, baked goods, pestos, and sauces. Walnut oil is also prized for its delicate, nutty flavour in dressings and gourmet cooking.

Walnut trees are large, long-lived, and majestic, with broad canopies and deep green pinnate leaves. They have been cultivated for thousands of years and are among the oldest tree foods known to humanity. One important characteristic is that walnuts produce a chemical called juglone, which can inhibit the growth of many nearby plants — a consideration when siting the tree in a garden.

How To Grow

Growing Walnuts

Walnut trees are long-lived and rewarding but require careful siting and patience. Grafted trees produce nuts much sooner than seed-grown trees and are the recommended choice for most gardeners.

Choosing a Variety

• English/Persian Walnut (Juglans regia): The most widely grown; produces large, thin-shelled nuts with a mild flavour. Suits temperate climates with cold winters and warm summers.
• Black Walnut (Juglans nigra): Produces smaller, harder-shelled nuts with a more intense flavour. More tolerant of varied conditions but takes longer to mature.

Site Selection

• Sunlight: Choose a position receiving full sun for at least 6–8 hours per day.
• Soil: Deep, fertile, well-drained soil with a pH of 6.0–7.5 is ideal. Avoid waterlogged areas — walnuts will not tolerate standing water.
• Space: Walnut trees grow very large. Allow at least 10–12 metres between trees, and site them well away from vegetable beds, as they produce juglone, a chemical toxic to many plants.
• Shelter: A sheltered position away from frost pockets protects spring blossom and young growth.

Planting

From seed:

1. Collect fresh nuts in autumn and remove the husks.
2. Soak seeds in water for 24 hours.
3. Cold-stratify by placing seeds in moist sand or peat in a refrigerator for 3–4 months.
4. Sow in spring at approximately 5 cm depth in deep pots or directly in the ground.

From grafted saplings (recommended):

1. Plant in early spring or autumn into well-prepared ground.
2. Dig a hole twice as wide as the root ball and equal in depth.
3. Ensure the graft union remains above soil level.
4. Backfill, firm, and water deeply.

Ongoing Care

• Watering: Water regularly and deeply during the first 2–3 years. Once established, walnut trees are moderately drought-tolerant.
• Mulching: Apply a thick layer of organic mulch around the base to retain moisture and suppress weeds. Keep mulch away from the trunk.
• Feeding: Apply a balanced fertiliser in early spring. After the first year, soil testing will guide further nutrient applications.
• Pruning: Prune in late winter while dormant to shape the tree and remove dead, damaged, or crossing branches. Avoid heavy pruning, as this can delay nut production.
• Pollination: Most walnuts are partially self-fertile, but yields are significantly improved by planting two or more trees nearby.

Harvesting

Harvesting Walnuts

Walnuts are typically ready to harvest in early to mid-autumn. Timing varies by variety and local conditions, but the signs of maturity are consistent.

Signs of Readiness

• The outer green husk begins to split and turn brown or black.
• Nuts begin to fall from the tree naturally.
• Shaking a branch causes ripe nuts to drop freely.

Gathering the Crop

• Allow natural drop: Most ripe nuts will fall on their own. Check under the tree regularly and collect promptly to prevent rot, mould, or damage by wildlife.
• Knock remaining nuts: Use a long pole to gently knock down nuts that haven't fallen. Take care not to damage branches.
• Wear gloves: Walnut husks contain juglone and tannins that will stain skin and clothing a deep brown. Old gloves and clothes are essential.

Husking

Remove the outer green or blackened husk as soon as possible after collection. Delay encourages mould. Tools such as husking rollers or a firm boot can help. Black walnuts have particularly tough husks requiring more effort.

Washing and Sorting

• Rinse the shelled nuts thoroughly in clean water to remove husk residue.
• Float test: Place nuts in a bucket of water. Sound nuts sink; hollow or poor-quality nuts float — discard the floaters.

Drying and Curing

• Spread clean nuts in a single layer on mesh trays or screens in a shaded, dry, well-ventilated area.
• Turn daily to ensure even drying.
• Curing takes 2–4 weeks depending on conditions. Nuts are ready when the shell is brittle and the kernel snaps cleanly when cracked.

Storage

• Store dried, unshelled walnuts in mesh bags or slatted boxes in a cool, dry location. They will keep for several months.
• Shelled kernels are best stored in airtight containers in a cool, dark place or frozen for up to 12 months.

Common Problems

Common Problems with Walnuts

Walnut Blight (Xanthomonas arboricola pv. juglandis)

A bacterial disease causing dark, sunken lesions on young shoots, leaves, flowers, and developing nuts. Infected nuts turn black and fail to develop. It spreads rapidly in wet spring conditions. Improve air circulation through pruning and avoid overhead watering. Copper-based sprays applied at bud burst can help reduce infection.

Walnut Leaf Blotch (Ophiognomonia leptostyla)

A fungal disease causing brown, irregular blotches on leaves, leading to early defoliation. Severe infections weaken the tree and reduce nut production over time. Rake and dispose of fallen leaves to reduce the spore reservoir. Fungicide applications may be warranted in persistently affected trees.

Walnut Husk Fly (Rhagoletis completa)

The larvae of this fly tunnel into the green husk, causing it to blacken and adhere to the shell, staining and sometimes tainting the kernel. Monitor with yellow sticky traps and apply appropriate insecticides at the adult emergence stage if populations are high.

Codling Moth (Cydia pomonella)

Larvae tunnel into developing nuts, causing premature drop. Pheromone traps are useful for monitoring adult activity. Kaolin clay, neem-based products, or targeted insecticide applications can reduce damage.

Aphids

Several aphid species colonise walnut foliage, causing leaf curling and honeydew deposits that lead to sooty mould. Natural predators (ladybirds, lacewings) usually keep populations in check; high-pressure water sprays or insecticidal soap can help with severe infestations.

Juglone Toxicity to Nearby Plants

Walnut roots, leaves, and husks release juglone, which is toxic to a wide range of plants including tomatoes, potatoes, apples, and many ornamentals. Ensure the tree is sited well away from vegetable gardens and sensitive plants.

Root Rot (Phytophthora spp.)

Waterlogged soils encourage root rot, causing decline and dieback. Ensure excellent drainage at planting time. Avoid irrigating close to the trunk.