General
Walnut is a long-lived, large nut tree valued for flavorful nuts, shade, and timber. English/Persian walnut (Juglans regia) is the main nut species in gardens; black walnut (J. nigra) and Manchurian walnut (J. mandshurica) are hardier but differ in nut and growth. Choose hardy cultivars for colder zones. Walnuts exude juglone, an allelopathic compound from roots, leaves, and husks that can inhibit sensitive plants—plan siting carefully. Requires space (8–12 m spread) and full sun. Catkins and female flowers are separate on the same tree and can be damaged by late spring frost; a compatible pollinizer improves set. Trees bear after 4–8 years from grafted plants (longer from seed).
Light
Full sun (6–8+ hours of direct light). Sheltered from cold spring winds if possible.
Soil type
Deep, well-drained loam with good calcium and organic matter. Avoid waterlogging and very shallow, compacted soils.
Water requirement
Moderate. Keep evenly moist during establishment (first 3–5 years). Deep, infrequent watering during dry spells; drought-tolerant once mature.
Nutrient requirement
Low to moderate. Light nitrogen in early spring on young trees; mature trees often need only compost/mulch.
Precultivation
Seeds require cold stratification: store fresh nuts (unhusked or cleaned) cool and slightly moist, then stratify 90–120 days at 1–5°C in damp sand/perlite. In late winter, sow one nut per deep pot (20–30 cm) with the seam vertical, 3–5 cm deep. Protect from rodents. Keep at 18–22°C for germination after stratification. For reliable nut quality and faster bearing, plant grafted trees rather than seedlings.
Planting
Best planted in spring once frost risk moderates and air temps are consistently above ~5°C. Choose a sunny, well-drained site with 8–12 m spacing from buildings and other trees. Dig a wide hole, loosen sides, and plant at the same depth as in the nursery pot; keep graft union above soil. Backfill with native soil (no heavy amendments), water deeply, and mulch 5–8 cm thick (keep mulch 10 cm from trunk). Stake only if windy exposure; remove stakes after 1–2 seasons. Protect trunk from deer/hares and sunscald (tree guard or whitewash). Avoid planting vegetable beds under the canopy due to juglone and root competition.
Pruning
Prune only in summer (JAS period) to avoid bleeding: mid-June to end of August. Train a central leader with well-spaced scaffold branches. Remove competing leaders, crossing/rubbing shoots, and dead/diseased wood. Avoid large cuts; make clean cuts just outside the branch collar. Do not winter-prune walnuts.
Maintenance
Water regularly for the first 3–5 years (20–40 L per week in dry periods). Maintain a weed-free, mulched rooting zone. In early spring, apply a light nitrogen feed for young trees or a ring of compost; avoid high nitrogen on bearing trees which can reduce nut quality. Do not till under the canopy. Collect husks and leaves; hot-compost thoroughly if reusing, as juglone breaks down with time and microbial activity. Monitor for walnut blight (black lesions on leaves/husks), anthracnose, cankers, and aphids; promote airflow, avoid overhead irrigation during bloom, and remove infected debris. Net or use wildlife deterrents if squirrels/magpies are an issue.
Harvest
Harvest when green husks split and begin to drop (typically mid-Sept to late Oct). Wear gloves—husks stain. Remove husks promptly, wash nuts, and cure in a single layer with good airflow at ~15–25°C for 1–2 weeks until kernels are crisp. Store in-shell nuts cool and dry; shelled kernels keep best refrigerated or frozen. Flavor improves after a short rest post-curing.
Common issues
• Poor nut set: lack of compatible pollinizer, frost-damaged catkins, or mismatched flowering types. Add a second cultivar with overlapping bloom. • Juglone injury to nearby sensitive plants—use tolerant species or raised beds with root barriers. • Bleeding from pruning cuts—result of off-season pruning; restrict pruning to summer. • Bacterial blight and leaf spots in wet springs; improve airflow and sanitation. • Wildlife theft (squirrels, crows).
Pollination
Wind-pollinated, monoecious. Partially self-fertile, but yields improve with a second, compatible cultivar. Note A/B flowering types (protandrous/protogynous) for overlap.
Companion plants
Understory and groundcovers tolerant of juglone and dry shade: periwinkle (Vinca minor), pachysandra, ivy (Hedera helix), sweet woodruff (Galium odoratum), lungwort (Pulmonaria), hosta, barren strawberry (Waldsteinia), wild strawberry (Fragaria vesca), ferns. Shrubs with some tolerance: blackcurrant (Ribes nigrum), sea buckthorn (Hippophae rhamnoides) at a distance.
Incompatible plants
Avoid juglone-sensitive plants near roots/dripline: tomato, potato, pepper, eggplant, apple, pear, blueberry, rhododendron/azalea, mountain laurel, hydrangea, white birch, asparagus.
