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How to Grow Walnuts USA | Care, Pests & Disease Control
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Named directly by RHS as affecting leaves; RHS does not specify a single named pathogen species so this is recorded at unspecified-fungus level rather than inventing one. RHS advises collecting and disposing of…
Walnut anthracnose
low
Named directly by RHS alongside walnut leaf blotch, affecting leaves; again no pathogen species is specified by RHS. Controlled the same way -- collecting and disposing of diseased leaves.
Walnut leaf gall
low
Named directly by RHS: pouch-shaped galls on the leaves, described as insignificant to tree health.
Crown gall
moderate
Agrobacterium tumefaciens
Named directly by UC ANR: bacterial growths (Agrobacterium tumefaciens) that reduce nutrient flow through the affected tissue.
Walnut blight
moderate
Xanthomonas arboricola pv. juglandis
Named directly by UC ANR: black lesions on catkins, nuts, leaves or shoots, worse in wet springs.
Named directly by RHS, which calls squirrels the single biggest threat to a crop and recommends plastic tree guards and raising lower branches to 1.8-2.5m; UC ANR notes trees "can live for centuries" but does not name…
Codling moth
low
Cydia pomonella
Named directly by RHS as damaging the nuts.
Scale insects
low
Diaspididae / Coccidae
Named directly by UC ANR, which recommends a dormant oil spray as treatment.
Deep (at least 5-6ft/1.5-1.8m), well-drained, permeable, fertile, moisture-retentive soil (UC ANR; RHS). RHS separately favours alkaline loam -- a broadly tolerant range from neutral to alkaline rather than a strict conflict with UC ANR's 6-7 figure.
Lifecycle
Deciduous nut tree. Wind-pollinated, monoecious with separate male catkins and female flowers on the same tree, but RHS describes it as only partially self-fertile -- cropping improves with a second, cross-compatible cultivar nearby. UC ANR (Marin Master Gardeners) gives the underlying reason: pollen is often shed by a tree's own catkins when its own female flowers are not yet receptive, so two different varieties planted together set a more reliable crop.
Water: Young trees: 4-12 gallons/day; larger trees: 20-40 gallons/day; water every 3-4 weeks through summer, or drip-irrigate May-October kept away from the trunk (UC ANR). Avoid frost pockets and exposed, windy sites -- both damage foliage and flowers (RHS).
Soil pH range
67
Span reflects genuine variation between the cited authorities, not a single agreed figure.
Plant young trees under 3m (10ft) tall during late autumn to winter, spaced 12-18m apart (RHS); UC ANR gives an overlapping 30-60ft spacing figure. Avoid pot-bound stock -- tap root damage is a real risk in young trees (RHS; UC ANR). Dig a hole twice the container's diameter with the root ball sitting about 2in proud of the soil, untangle roots and remove shoots within 6in of the soil, then mulch 3in clear of the trunk (UC ANR). Stake, water in dry spells (RHS). Caution: walnut roots and fallen leaves/husks release a natural growth inhibitor (juglone) that can suppress nearby plants -- do not plant sensitive species close by (UC ANR).
Establishment care: watering and feeding
3
Young trees need 4-12 gallons of water a day, larger trees 20-40 gallons a day; water every 3-4 weeks through summer, or drip-irrigate May-October kept away from the trunk (UC ANR). Feed with compost in the first two years; from year three, apply 5-7lb urea or 90-150lb manure in early spring (UC ANR).
Pruning and training
3
Train with either a central leader, or by removing the leader to restrict size; pinch side shoots at the 5th or 6th leaf; avoid hard pruning (RHS). Prune only between mid-summer and early autumn -- walnut is prone to heavy "bleeding" from cuts made at other times of year (RHS). UC ANR's seasonal task list separately names winter as a time to thin crowded areas; the two sources are not reconciled here and both are given as stated.
Flowering and pollination
6
Wind-pollinated, with separate male catkins and female flowers on the same tree. RHS describes the tree as partially self-fertile but says cropping is improved by cross-pollination -- cv. Broadview is given as an example. UC ANR explains the underlying reason: a tree's own pollen is often shed when its own female flowers are not yet receptive, so two different varieties planted together set a more reliable crop.
Fruiting and harvest
8
Nuts ripen in autumn -- UC ANR gives mid-September to early November -- splitting from their fibrous husk. Harvest daily: very vulnerable to birds and squirrels once ripe (RHS). Remove the fibrous casing with a wire brush before storage and dry in a cool oven at maximum 40C (RHS); UC ANR dries hulled nuts for 3-4 days and stores them airtight, with frozen shelled walnuts keeping up to a year.
When to pick: Nuts ripen and split from their fibrous husk in autumn -- UC ANR gives mid-September to early November. Harvest daily: RHS warns nuts are very vulnerable to birds and squirrels once ripe.
Storage
Remove all traces of the fibrous casing with a wire brush before storage, then dry in a cool oven at maximum 40C (RHS). UC ANR: dry hulled nuts for 3-4 days and store in airtight containers; frozen shelled walnuts keep up to a year.
Site: well-drained, fertile, moisture-retentive, alkaline loam preferred, tolerates most soils; avoid frost pockets/exposed sites (wind and spring frost damage foliage/flowers); full sun, light shade tolerated when young. Planting: young trees under 3m during late autumn to winter; space 12-18m apart; avoid pot-bound stock (tap root damage); stake, water in dry spells, mulch with well-rotted compost. Pollination: partially self-fertile, cropping improved by cross-pollination -- cv. Broadview example. Pruning: central leader or leader-removal to restrict size; pinch side shoots at 5th/6th leaf; avoid hard pruning; prune only between mid-summer and early autumn -- prone to bleeding at other times. Harvest: nuts ripen in autumn; harvest daily, very vulnerable to birds and squirrels; remove fibrous casing with a wire brush before storage; dry in a cool oven at maximum 40C. Pests/diseases: grey squirrels (use plastic tree guards, raise lower branches to 1.8-2.5m), codling moth damages nuts, walnut leaf blotch and anthracnose affect leaves (control by collecting/disposing of diseased leaves), walnut leaf gall causes insignificant pouch-shaped galls. Regional limit: nut crops generally unreliable north of the Midlands. Propagation: cuttings difficult (poor rooting); whip grafting or T-budding onto one-year seedlings; sow fresh seed 3cm deep, seedlings ready for T-budding the following August.
Site: sunniest spot, sheltered from wind, 30-60ft spacing. Soil: deep, well-drained, permeable soil at least 5-6ft deep, pH 6-7. Planting: hole twice container diameter, root ball 2in proud of soil surface, untangle roots and remove shoots within 6in of soil, mulch 3in clear of trunk. Caution: walnut produces a growth inhibitor (juglone) that can negatively affect nearby plants -- do not plant sensitive species close by. Water: young trees 4-12 gallons/day, larger trees 20-40 gallons/day; water every 3-4 weeks through summer or drip-irrigate May-October away from the trunk. Fertilizing: compost in years 1-2; from year 3, 5-7lb urea or 90-150lb manure in early spring. Pollination: wind-pollinated but needs two different varieties planted together, since a tree's own pollen often sheds when its own female flowers are not receptive. Seasonal pruning notes: winter -- thin crowded areas. Harvest: nuts mature mid-September to early November; dry hulled nuts 3-4 days; store in airtight containers, frozen shelled walnuts keep up to a year. Pests/diseases: crown gall (bacterial growths reducing nutrient flow), walnut blight (black lesions on catkins, nuts, leaves or shoots, worse in wet springs), scale insects (treatable with dormant oil spray). Climate: a good choice for Marin's hottest microclimates; trees can live for centuries.
2 independent sources are cited for this crop. Where they disagree - soil pH is the clearest case - every figure is preserved rather than averaged into false precision.
Frequently Asked Questions
What soil pH do walnuts need?
A pH of about 6–7. That span reflects genuine variation between the authorities we cite rather than a single agreed figure — the References section lists each source's exact range.
What problems affect walnuts?
Our data links 5 diseases and 3 pests to this crop. See the sections above for each one and how to manage it.
Plan next season before the problems start
Almost everything on this page resolves to your own frost dates rather than the calendar — the last spring frost moves by roughly two months between zone 3 and zone 10. The USA Garden Planner works from your zone so the timing is already decided before the season starts.
US vegetable growing guides · Adapted for USDA hardiness zones and US frost dates
Every SoilCommander guide is written and maintained by our editorial team for real US growing conditions, adapted to USDA hardiness zones and US frost-date data, with Cooperative Extension growing advice cited directly where a crop-specific source exists.
Sketch your exact plot shape, pick your crops, and get a spacing-accurate bed layout with companion pairings and a rotation plan. Spacing, companion pairings and rotation work the same in any climate — pair the layout it gives you with the USA planting calendar for your own frost-date timing.
