Photo: Thesupermat — CC BY-SA 3.0 · source
Survives zone 4 through 9
Harvest calendar
Best planted in early spring after your last frost, or in fall before the ground freezes, depending on your climate.
Persian (English) walnut is the world's dominant commercial walnut — the species behind virtually every walnut sold in stores — grown on 'Paradox' rootstock across California and other Mediterranean-climate regions for its comparatively thin shell and mild, buttery-flavored kernel.
- Hardiness
- Zone 4–9
- Habit
- Tree
- Edible part
- Nut
- Ripens
- Sept–Oct
- Mature size
- Large tree 15–25 m — NOT containerable
- Light
- Full sun
- Soil pH
- 6.0–7.5 (near-neutral; lime-tolerant)
- Environment
- Montane
- Native range
- Native from the Balkans and Caucasus through Central Asia and the Middle East (Azerbaijan, Iran, Iraq, Turkey, Turkmenistan, Afghanistan, Pakistan) to the Himalaya, growing wild in mountain forests, generally on a northerly aspect in the western part of its range and a southerly or westerly aspect farther east.
- Status
- Cultivated
- Years to fruit
- 5–10 yrs
- Growth speed
- Moderate to fast — seedling trees typically take 6–15 years to begin bearing, while grafted cultivars can start cropping within about 5 years and reach general maturity around 10–15 years.
- Spacing
- 1200 cm (472 in) apart — about 144 m² (1550 sq ft) per plant
- Leaf shape
- Odd-pinnate compound leaves 25–40 cm long with 5–9 leaflets in opposite pairs plus one terminal leaflet (the largest); leaflets are ovate to obovate with entire to finely serrated margins, the largest 10–18 × 6–8 cm and the basal pair much smaller (5–8 cm). New leaflets emerge purple-bronze, maturing to shiny green, and are strongly aromatic when crushed.
- Root system
- Develops a deep taproot and is notably intolerant of root disturbance, so seedlings and young trees should be planted into their permanent positions as soon as possible.
- Fruit description
- Nuts ripen in autumn with a somewhat rubbery texture when fresh, improving markedly on drying; the kernel is about 65% fat and 15% protein with a mild, sweet, buttery flavor — noticeably milder than black walnut. Shell thickness varies by cultivar but is generally much thinner and far easier to crack than in J. nigra. The seed oil has a pleasant flavor for salads or cooking but goes rancid quickly if kept long.
- Propagation
- Seed is best sown as soon as ripe, one per deep pot in a cold frame, protected from rodents and birds; alternatively it can be stored cool and moist over winter and sown in early spring, sometimes needing cold stratification. Named varieties are propagated by budding. Because walnut is difficult to root from cuttings, commercial clonal propagation increasingly relies on tissue culture (micropropagation). Commercially, nearly all orchard trees are grafted onto 'Paradox' rootstock (a J. hindsii × J. regia hybrid) for vigor, tolerance of difficult soils, and resistance to Phytophthora and nematodes. Seedling trees take 6–15 years to fruit, while grafted cultivars typically begin cropping within 5 years.
- Pollination
- Wind-pollinated and self-fertile, though — as with the genus generally — a second cultivar of the opposite flowering type markedly improves nut set and fill; commercial growers deliberately pair protandrous and protogynous cultivars for this reason, and cross-pollination distances of up to 200 ft between compatible trees are commonly recommended.
The edible parts listed above are a starting point, not a field guide. Identify a plant with certainty — ideally against a local authority — before eating any part of it, and read the full disclaimer. Spotted something wrong? Report it.
Growing guide
Fertilizing. Prefers a slightly alkaline, heavy loam but succeeds in most soil textures — light, medium or heavy — and tolerates a wide pH range (4.5–8.2) provided drainage is good; the tree prefers moist soil but cannot tolerate shade. Good drainage and soil structure matter more to this species than heavy feeding, and commercial orchards typically fertilize according to soil and leaf-tissue nutrient testing rather than a fixed schedule.
How it spreads. A single-trunked, non-suckering tree — it spreads only by seed dispersal, not by root suckers or colonizing growth.
Growing tips. By far the most commercially important walnut species in the world — this is the tree behind essentially every walnut sold in grocery stores, with California alone producing about 99% of the U.S. crop, almost entirely on 'Paradox' rootstock. It is comparatively resistant to thousand cankers disease relative to J. nigra, though not immune — it can still be attacked where walnut twig beetle populations are high. Dormant trees are very cold-hardy (down to about -27°C), but flowers and young spring growth are frost-tender and can be killed by even brief exposure to -2°C, making late spring frosts the main climatic risk; the species also prefers a warm, continental climate to properly ripen its nuts and wood, often failing to do so fully in cool, damp climates such as Britain's. It is notably susceptible to honey fungus, and pruning should only be done in late summer/early autumn or full dormancy, since wounds bleed profusely and can seriously weaken the tree otherwise. Juglone is present as in other walnuts — inhibiting tomatoes, potatoes, apples and white pines beneath and around the canopy — but is generally considered less potent than in J. nigra.
Companion planting. Also produces juglone, but in much lower concentration than black walnut — toxicity to nearby plants is rarely observed in practice.
Grow journal
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