Walnut

Butternut (White Walnut)

Direct-seed nuts in fall, or stratify 120 days for spring

The easiest route is to plant nuts in fall, one to two inches deep, under a straw or sawdust mulch up to an inch thick, then pull that mulch in spring if it has crusted or compacted enough to block emergence. To sow in spring instead, soak the seed 3 to 12 hours, air dry it a few hours, then layer it in a barely moist medium such as peat, sphagnum, or sand and hold it between 32 and 40 degrees F for 120 days. Gather seed from as many mother trees as you can rather than a large pile from one tree. Butternut seed will not germinate until it has had about 120 days of moist chilling, and spreading collection across many mothers preserves the considerable genetic diversity that canker-hit butternut populations still carry.

⚠ Squirrels take fall-sown nuts heavily, so protect the bed. Inspect seedlings carefully as they grow, because butternut seed can itself carry the canker fungus and infect the resulting seedling.

Butternut (White Walnut)

Full sun, a well-drained site, and never just one tree

Plant butternut on deep, well-drained ground with good moisture — the rich woods, coves, stream benches, terraces and slopes it occupies naturally — and give it full overhead sunlight. Young trees will take some competition, but a mature butternut has to reach the overstory to survive. Put at least two butternuts near each other. Butternut produces juglone, which selectively inhibits the growth of associated plants: keep juglone-sensitive species — tomatoes and several conifers are the ones documented for butternut — out of the tree's future root zone and dripline, and do not mulch them with butternut leaves, bark, or husks. Butternut carries male catkins and female flowers on the same tree, but they usually do not open at the same time on any one individual, so a solitary tree pollinates itself poorly, and a lack of butternut trees in the immediate vicinity limits pollination and fruit formation. The tree also produces juglone, concentrated in root tissue and fruit husks with lesser amounts in the leaves, catkins, buds, and inner bark, which selectively inhibits susceptible plants.

⚠ Nursery stock sold as butternut is frequently a Japanese walnut hybrid, or buartnut (Juglans x bixbyi), which looks similar and is often mislabeled — in some places hybrids or their offspring are virtually the only 'butternuts' to be found. If keeping the native species matters to you, confirm the seed source; Purdue FNR-420-W covers field identification of butternuts versus hybrids.

Butternut (White Walnut)

About an inch of water a week, delivered at the ground

When rain falls short, give the tree roughly one inch of water per week through the growing season using drip irrigation or a soaker hose at the root zone rather than an overhead sprinkler. Fertilize only to correct a deficiency that a soil nutrient test actually shows. Vigor is essentially the only lever a grower holds against butternut canker, since trees in good health delay mortality longer, and watering at the ground keeps water off the bark rather than splashing it, which is how the fungus moves its spores.

Black Walnut

Nitrogen before growth resumes, the bigger of two feedings

On bearing trees, broadcast urea 46-0-0 over the whole orchard floor at a rate supplying about 60 pounds of actual nitrogen per acre while the tree is still dormant and before budbreak. Follow with a second, smaller application of about 40 pounds of actual nitrogen per acre in fall, around harvest. Sample leaflets from late June to early August for a leaf analysis to decide whether phosphorus, potassium or micronutrients are also needed. Added nitrogen stimulates leaf growth and increases annual pistillate flower production, so the nitrogen you apply now is helping decide next year's crop, not just this year's leaves. Maintaining healthy foliage is the only way the tree banks enough carbohydrate to fill this season's nuts and still sustain next season's flowering.

English (Persian) Walnut

Fertilize in spring only if the tree asks for it

Apply fertilizer only in spring as active growth begins, and only if the tree is growing poorly or bearing lightly. A healthy walnut carrying a decent crop usually needs nothing. Judge by shoot growth and leaf color rather than fertilizing on schedule. Walnut is a large, deep-rooted tree that forages a lot of soil on its own, and feeding a tree that is already growing well pushes soft late growth instead of nuts.

Butternut (White Walnut)

Crown release: cut the neighbors, not the butternut

Remove the trees whose crowns are directly competing with the butternut, especially where its crown is being overtopped or pinched between neighbors. Do this in the dormant season and keep felling away from the butternut's trunk and root flare so you do not wound it. Butternut is shade-intolerant and has to hold a place in the main canopy to survive, and a tree of good vigor in a competitive crown position is better able to delay mortality from canker infection.

⚠ Do not strand a seed-bearing butternut alone in a fresh opening. Field experiments that left butternuts standing as seed trees in harvest openings saw those trees die rapidly, so arrange openings near the tree rather than around it.

Black Walnut

Dormant structural pruning of bearing trees

Prune while the tree is fully dormant and leafless. Take out low-hanging, broken, weak, dead or diseased branches, remove water sprouts, and eliminate crossing or rubbing limbs. Remove any branch that meets the trunk at a narrow crotch entirely. Aim for two or three well-spaced laterals staggered around the trunk. Never cut a branch larger than one-third the diameter of the main trunk, and do not paint the wounds. Dormant pruning promotes new growth while summer cuts inhibit it, and the narrow-crotch branches you remove now are the ones that split out under a heavy nut crop later. Painting wounds traps moisture and encourages decay rather than preventing it.

English (Persian) Walnut

Prune late summer through fall, not in spring

Train young trees to a central leader or modified central leader, letting four to five scaffold branches space out along the trunk before heading the leader. Prune from late summer into late fall, taking out crossing, broken, and low limbs. Walnut often throws multiple competing leaders after frost or insect damage kills a terminal bud, so cut back to a single leader each year. Walnut pruned in late winter or spring bleeds sap heavily from the cuts, and the tree's structure is set by these early cuts because a walnut carries its crop on limbs that must hold decades of weight.

Butternut (White Walnut)

Cut out branch cankers in dry dormant weather, and cut low

If you catch a canker early on a smaller branch, cut six to eight inches below the visible canker margin and destroy the removed wood. Disinfect the blades between every single cut for at least 30 seconds in a 10 percent bleach solution or, preferably, 70 percent alcohol; if you used bleach, rinse and oil the tool afterward so it does not rust. Leave cankers on the trunk and root flare alone, because they cannot be pruned out. The fungus enters through wounds and through leaf and branch scars, and its spores travel mainly in rain splash, which then washes new infections down the trunk from infected branches above.

⚠ Pruning itself raises the risk of canker infection on butternut, so make only the cuts you genuinely need. A tree already carrying trunk or root-flare cankers will not be saved by pruning.

Black Walnut

Trap for walnut husk fly before the husks soften

Hang yellow sticky traps baited with an ammonium carbonate lure in the shadiest, dampest parts of the planting, which is where the flies concentrate. Check them two or three times a week. Crush the trapped females and look for eggs: the first female carrying eggs is your spray trigger. You can also inspect husks for small stinglike punctures that darken to black spots near the stem end, though by then the damage is already done. Husk fly has one generation a year and adults emerge over a long window from early summer into early fall, so there is no fixed date to spray by. Trap catch is the only way to know when your own flies are laying.

Black Walnut

Thousand cankers disease: check the crown, and never move the wood

Look up in midsummer for yellowing and thinning in the upper crown, then for flagging - wilted leaves hanging on dead branches. Peel bark from a dying limb and look for tiny beetle exit holes and the galleries beneath. Suspect it more strongly if several walnuts at one site are declining together. If a tree is confirmed or has to come down, keep every piece of the wood local: chip it, bury it, or hold it in isolation. The walnut twig beetle carries the Geosmithia morbida fungus, and each of its thousands of small cankers kills a patch of cambium until the branch girdles. Bark-on logs stay infectious for well over a year, so a single piece of firewood moved down the highway can start an outbreak hundreds of miles from the source. Human wood movement, not beetle flight, is what spreads it.

⚠ There is no reliable chemical control. Trunk sprays of permethrin or bifenthrin show only limited effect at best, and soil neonicotinoids are negligible once symptoms appear. Because black walnut is an edible nut crop, pesticide options are severely restricted - do not improvise a treatment.

English (Persian) Walnut

Hang yellow sticky traps for walnut husk fly by early summer

Hang yellow sticky traps baited with ammonium carbonate in dense foliage on the north side of the tree by about June 1, and check them at least twice a week, preferably three times. Watch for a sharp jump in the catch, for the first female carrying eggs, or for the first sting on a husk - any of the three means it is time to treat. Husk fly has one generation a year and the adults emerge over a long stretch from early June into September, so only trapping tells you which weeks matter at your site. Once eggs are laid under the husk the larvae are out of reach of any spray.

Butternut (White Walnut)

Butternut canker: survey the trunk and crown while the leaves are out

With the canopy fully leafed out, look for sunken elliptical cankers with inky black centers and whitish margins, starting where they start: at leaf scars and buds. Then check the main stem, the base of the tree, and exposed roots, where cankers concentrate and coalesce. Apply the Forest Service retention rule: keep any tree with more than 70 percent live crown and cankers on less than 20 percent of the combined circumference of the bole and root flares, and keep any tree with at least 50 percent live crown and no cankers on the bole or root flares at all. Judge live crown from the upper and outer limbs only, because interior and lower branches die from ordinary shading. Butternut canker is fatal and has cut living butternuts by as much as 80 percent in some states, and there is no practical way to prevent infection, so the decision that actually matters is which trees you keep and breed from rather than which product you spray.

⚠ Do not read a healthy-looking butternut as a resistant one: no butternut is currently proven canker resistant. Even an isolated tree is exposed, because associated hickory, cherry, and oak can act as reservoirs of the fungus.

Black Walnut

Anthracnose: one well-timed fungicide once the stigmas turn dark

Watch the female flowers rather than the calendar. As soon as the pistillate flowers are pollinated, when the ovule starts to swell and the stigmas turn brown or black, spray azoxystrobin (Abound) or trifloxystrobin (Flint). A single application at this exact moment often carries the tree all season. On your earliest-flowering cultivars, or in a wet spring, follow with a second spray 10 to 14 days later. The fungus overwinters on last year's decaying leaves and twigs and infects the new leaves just as they reach full expansion, so the spray has to land in that narrow window. Miss it and the tree defoliates by August, losing the photosynthesis that fills this year's kernels and sets next year's flowers.

⚠ This spray goes on after pollen shed is finished, never during catkin bloom. Follow the label rate and interval; rotate actives between the strobilurin products to avoid resistance.

Black Walnut

Walnut curculio: insecticide in the same post-pollination window

Once the nutlets are pollinated, adult curculios climb or fly into the canopy to lay eggs in the young fruit. Spray carbaryl (Sevin 80W) or phosmet (Imidan 70WSB) in this same window; the timing overlaps the anthracnose fungicide, and if the labels allow it the two can go in one tank. Hang trunk-mounted cone traps afterward and make a second application only if they show continued curculio activity. The female carves a crescent-shaped gouge in each small nutlet and lays eggs inside; as the larvae feed the tree aborts those nuts, so curculio can strip a large share of the crop before midsummer. Hitting the adults before egg-laying is the only point where the damage is preventable.

⚠ Carbaryl is highly toxic to bees - mow or remove flowering groundcover under the tree before you spray. Several of the alternatives on this list (Warrior, Asana XL, Lorsban 4E, Nufos 4E) are restricted-use pesticides requiring an applicator license. Follow the label for rate and pre-harvest interval.

Black Walnut

Walnut husk fly: bait spray as the nuts begin to ripen

Once traps show the first female carrying eggs, and shortly before the nuts start to ripen, spray spinosad and add a feeding attractant such as a protein bait or molasses to the mix. Repeat on a 7 to 14 day interval while flies are active, but stop once you are within one month of harvest - eggs laid later than that will not have time to develop and cause damage. If you can harvest, hull and wash each cultivar promptly as it ripens, you can skip the insecticide entirely and simply beat the maggots to the husk. The insecticide is aimed at the adult flies, which must feed on the bait droplets to be killed - once eggs are under the husk surface, nothing you spray reaches the maggots. Their feeding turns the husk black and the leaking juice stains the kernel dark and strong-tasting.

⚠ Spinosad is the only home-use option for husk fly and is only partially effective. Observe the pre-harvest interval on your product: registered walnut materials range from 0 to 28 days - the GF-120 spinosad bait is 0 days, while phosmet (Imidan) requires 28 days before harvest. Spinosad is toxic to bees while the spray is wet, so apply in the evening and keep it off flowering groundcover. Several alternative husk fly materials (Lorsban 4E, Nufos 4E, Warrior) are restricted-use pesticides requiring an applicator license.

English (Persian) Walnut

Walnut husk fly: spray on a 7-14 day interval, and stop a month out

Spinosad is effectively the only home-use insecticide for husk fly, and it must be mixed with a bait to work. Spray every 7-14 days until about a month before harvest, then stop. Husk fly maggots stain and rot the husk, which then stains the shell. Eggs laid within about a month of harvest cannot develop in time to damage the nut, so spraying past that point achieves nothing.

⚠ The label PHI is 1 day, but the PRACTICAL cutoff is roughly 30 days before harvest - stop then, not at the legal minimum. UC IPM notes spinosad 'might be only partially effective' even so. Malathion is 7 days. Neither carbaryl nor pyrethrins appear in UC IPM's husk fly treatment table at all, so they have no supported use here.

English (Persian) Walnut

Dormant oil in late winter for scale, aphids, and mites

Before buds swell, or in late winter just as buds begin to show their first green, spray a superior-type petroleum horticultural oil to cover the bark and twigs thoroughly. Spray only when daytime temperatures are between 40 and 45 degrees F with no frost forecast overnight, and finish by noon so the tree dries. Scale, aphid eggs, and mites overwinter exposed on the bark with no leaves to shield them, and the oil kills by smothering, so this is the one window where full coverage is possible.

⚠ Oil applied below 40 degrees F or ahead of an overnight frost can injure the tree - check the forecast before spraying, and follow the label.

English (Persian) Walnut

Walnut blight: copper as buds break and catkins expand

Spray a fixed copper fungicide when about 30 to 40 percent of the buds reach the prayer stage, when the first leaflets stand upright and pressed together before unfolding, and repeat 7 to 10 days later. Keep repeating through a prolonged wet spring, since each rain brings a new infection period. Few new infections occur after about May. Commercial growers facing copper resistance tank-mix mancozeb with the copper; mancozeb is a commercial-use material and is not part of a home program - home growers should use fixed copper or Bordeaux mixture alone, which is what UC IPM recommends for home and landscape walnuts. The blight bacterium Xanthomonas arboricola pv. juglandis overwinters inside dormant buds and washes out with rain onto the emerging shoots and young nuts, so the copper has to be on the tissue before the rain moves the bacteria, not after symptoms show.

⚠ Mancozeb is a commercial product from UC IPM's agricultural guidelines, not a home-orchard material - do not buy or apply it as a homeowner; use fixed copper or Bordeaux mixture. Copper resistance is common in Sacramento Valley orchards, so copper alone may underperform there. Thorough coverage of all green tissue is needed. Homeowners should not attempt to spray trees over 10 feet tall - hire a commercial applicator. The label is the law.

English (Persian) Walnut

Walnut husk fly: spray on the trap trigger, before eggs are laid

When traps show a sharp increase, an egg-carrying female, or the first sting, spray spinosad promptly and repeat according to the label while trap catches continue. Aim at the husks, where the flies lay. WSU's home-garden walnut schedule also lists kaolin clay (Surround At Home) as an alternative that deters egg-laying by coating the husk. Females lay eggs in groups of about 15 beneath the husk surface and the larvae feed inside for three to five weeks, staining the shell and ruining kernel quality, so the spray only works if it kills adults before egg-laying.

⚠ Never spray insecticide while flowers are open - WSU's schedule states plainly: don't apply insecticides around blooming flowers. Pre-harvest intervals vary by product - spinosad bait (GF-120) is 0 days, but phosmet (Imidan 70W) requires 28 days before harvest. Follow the label PHI for the product you use. The label is the law.

English (Persian) Walnut

Clean up every last nut to break the husk fly cycle

After harvest, pick up all remaining nuts from the ground, including the wormy and blackened ones. Seal infested nuts in large black trash bags and leave the bags in the sun for two weeks to kill the larvae before disposing of them. Do not compost infested husks. Husk fly larvae finish feeding inside fallen husks and then drop into the soil to overwinter as pupae under the tree, so every nut left on the ground is next summer's flies - and some pupae stay dormant more than two years.

Butternut (White Walnut)

Guard the trunk before the rut

Put a rigid trunk guard or a fenced cage around young butternuts ahead of the autumn rut, and keep browse protection in place until the leader is clear of deer reach. White-tailed deer favor butternut foliage and rub their antlers on the stems, and every rub is a torn bark wound — precisely the kind of opening the canker fungus infects through.

Black Walnut

Harvest black walnuts promptlySep – Oct

Gather fallen yellow-green husked nuts, remove hulls promptly, wash, and dry in shallow layers for two to three weeks. Prompt hulling and drying protect kernel flavor and storage quality.

⚠ Wear gloves; hulls stain and contain juglone.

Black Walnut

Hull within days of gathering, then wash and air-dry

Nuts are ripe when you can press your thumb into the hull and leave an indentation. Gather fallen nuts regularly and hull them promptly while the husks are still spongy. Wash the hulled nuts in a chlorine bath of one teaspoon of regular household bleach per gallon of water to remove remaining hull and disinfect them, discarding any that float. Spread them on screen racks in a cool, well-ventilated place to air dry for two to three weeks. Never use heated air. Store the cured kernels in the freezer. The longer a fully ripened husk stays on the nut, the darker the kernel becomes and the greater the risk of post-harvest spoilage, and a lingering husk is also what husk fly maggots are living in. Nuts that float are poorly filled and not worth cracking.

⚠ Wear rubber gloves - the hull juice permanently stains skin, clothing and concrete. Do not compost the hulls; they carry juglone, which suppresses tomatoes, potatoes and other sensitive plants.

English (Persian) Walnut

Gather at hull split and dry the nuts down promptly

Harvest once the hulls have split and the nuts begin to drop, and pick up everything on the ground right away rather than letting it lie. Hull the nuts, then dry them with warm moving air at 95 to 105 degrees F until the kernels snap rather than bend. Nuts left on damp ground pull moisture back through the shell, which stains the shell and lets mold take hold in the kernel, and the loss happens in days, not weeks.

⚠ Do not dry above about 105 degrees F - excess heat makes the oil in the kernel go rancid and darkens the nut.

Butternut (White Walnut)

Pick once half the husks give to a thumb

Begin harvesting when about half the fruits yield to finger pressure, which is roughly when the first 10 percent of them have fallen. Knock the clusters down with a long pole or by tossing a throw bag and line over the limbs rather than waiting for a ground fall. Discard the earliest nuts on the ground: they are typically wormy or have shriveled kernels. Hull promptly — a pressure wash removes hulls that have already softened, and firm hulls can be cracked by rolling them under a vehicle wheel on a hard surface, then rinsed clean. The nut is mature once its husk softens and yields to a finger, and squirrels begin taking the crop from that same moment, so waiting for the nuts to drop on their own usually means losing them.

⚠ Wear gloves. The husks are rich in juglone and were historically used to make orange and yellow dye, so they stain skin, clothing, and concrete. Pole gently: wounds invite canker infection, and canker-weakened limbs can break without warning overhead.