How to grow a walnut tree

Identifying walnut trees

Walnut trees are large, with wide-spreading crowns and thick trunks. Young trees have smooth, olive-brown bark which matures to silvery-grey and develops fissures. Walnut trees are monoecious (with male and female flowers on the same tree). Male flowers are on pendulous catkins, 5-15cm long. The wind-pollinated female flowers grow in small, upright clusters. Walnut leaves are pinnate with leaflets arranged in pairs on either side of the stem. There are usually between five and nine oval, smooth-edged leaflets.

English walnut could be confused with black walnut (Juglans nigra) which is also planted in the UK as an ornamental tree. Black walnut can grow larger – up to 40m, and it has darker, more heavily ridged bark. Leaves have more leaflets than English walnut. They are toothed, unlike English walnut leaflets, and taper to a point rather than being rounded.

Size: height and spread

Walnuts are large trees that can grow to 30m, with a spread of up to 15m. They are fairly slow-growing, but grow strongly as young trees and can reach their final height within 20 to 50 years. Walnut trees can live for over 200 years in their natural habitat.

Value to wildlife

Walnuts are eaten by mammals such as grey squirrels and mice. It’s thought that the walnut has become naturalised in hedgerows, woodland and other areas of lowland Britain partly due to squirrels, and birds such as rooks, hoarding the nuts. Walnut leaves are the foodplants of invertebrates such as small emperor moth caterpillars, the large walnut aphid and the European stag beetle.

How to grow a walnut tree

English walnut will grow in moist but well-drained soil in full sun. Once established, walnut trees are easy to grow and fairly low maintenance.

Where to plant a walnut tree

English walnut is suitable for growing as a specimen tree in large gardens and parks. Avoid planting walnut trees in frost pockets or exposed areas. Walnut trees can be grown as ornamentals in the UK, but nut crops are less likely to be successful outside southern England.

How to plant walnut

Plant bare-root walnut trees between November and March when they're dormant. Trees that are sold in pots can be planted year-round, though avoid hot and freezing weather. Late autumn or winter is the best time to plant a walnut tree.

1. Soak bare-root and pot-grown trees before planting
2. Prepare the ground well, adding compost to the soil
3. Dig a square planting hole
4. Plant with the top of the rootball, or soil mark on bare-root trees, at soil level
5. Back-fill the planting hole and gently firm soil around the base of the tree
6. Stake the tree to avoid wind rock. If you are planting a pot-grown tree, do this at a 45 degree angle to avoid damaging the rootball
7. Use a tree tie to secure the stake to the tree
8. Water your tree well

How to care for a walnut tree

During the first full growing season, keep the tree watered during dry spells, watering thoroughly once every few days to encourage deep roots to develop. Keep the ground around the base clear of grass and weeds for at least a one-metre circle to avoid competition for water and nutrients. Add a mulch of well-rotted compost around the base of the tree in spring. Walnut tree care is minimal after the first couple of years once the tree is established.

How to prune walnut

Walnut trees require little pruning. Rather than routine pruning, simply remove dead, damaged or diseased branches, and those that are crossing, between mid-summer and early autumn to avoid bleeding (when the tree loses sap through pruning cuts). Walnut trees can be allowed to develop a central leader, or this can be removed to restrict the size of the tree and encourage the growth of side shoots. Walnuts should never be hard pruned.

How to harvest walnuts

Always plant grafted, named varieties as they will fruit as younger trees and produce better nuts. Most walnut varieties are self-fertile, but two or more trees of different varieties are needed to produce the best crops. English walnuts are ready to harvest for pickling well before the shells have hardened, in June. Use rubber gloves when preparing walnuts to prevent them staining or irritating your hands.

Pick walnuts in autumn, when the hulls begin to crack and show the shell within. Remove the hulls as soon as possible with a wire brush to avoid mould developing. Check a couple of shells before drying the batch to make sure they've got fully developed walnuts inside. If they're fully formed, dry the remaining nuts and store in a cool dry place. Walnuts are thought to have many health benefits, including having anti-inflammatory properties and being good for the brain.

Pests and diseases of walnut trees

Common walnut may have issues with grey squirrels, which can strip the entire tree of nuts, and walnut blister mites can cause galls to form on leaves, although these are not damaging to the overall health of the tree. Walnuts are also susceptible to aphids, codling moth and fungal diseases such as honey fungus, coral spot and walnut leaf blotch, which can cause early leaf fall and damage fruits. Walnut blight can have serious consequences for trees, but there are blight-resistant varieties available.

Walnut trees also secrete biochemicals that inhibit the growth of other plants, although the mechanism is not fully understood. Studies have demonstrated negative effects on tomato and cucumber seedlings, and strawberry plants.

Types of walnut tree

Juglans regia ‘Broadview’ – a more compact self-fertile walnut that fruits earlier than other varieties, producing medium-sized walnuts from its third or fourth year of growth. One of the best varieties to grow in the UK. Height x Spread: 7m x 6m

• Buy Juglans regia ‘Broadview’ from Suttons

Juglans regia ‘Lara’ – this heavy-cropping variety is self-fertile, disease-resistant and produces walnuts with thin shells. H x S: 7m x 6m

• Buy Juglans regia ‘Lara’ from Crocus

Juglans regia ‘Europa’ – this extremely compact variety has been bred for smaller spaces and crops as a young tree at around three years of age. H x S: 3.5m x 3.5m

• Buy Juglans regia ‘Europa’ from Thompson & Morgan

Juglans regia ‘Buccaneer’ – a beautiful self-fertile walnut variety with an upright habit. The rounded nuts are good for pickling. H x S: 12m x 8m

• Buy Juglans regia ‘Buccaneer’ from Dobies