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A Forager’s Year

No. 85

Black walnut

Juglans nigra

Fruit half-grown green fruits, husk and all, before the shell forms (pickled or steeped in liquor)

Drawing: Britton & Brown, Illustrated Flora (1913)

Find
Common in the right habitat
Effort
Quick kitchen prep
ID risk
Beginner
Origin
native
Uses
  • Wine & spirits
  • Pickles

Season

  1. Jan
  2. Feb
  3. Mar
  4. Apr
  5. May
  6. Jun
  7. Jul
  8. Aug
  9. Sep
  10. Oct
  11. Nov
  12. Dec

in season peak

Picking: The rules are unclear. Ask the park. See Where you may pick.

What these mean

Find

1 Everywhere · 2 Common in the right habitat · 3 Patchy · 4 Elusive. This is about how much there is, not whether you may pick it. It is based on iNaturalist sightings within 25 km (about 15 miles) of downtown DC, counted on October 3, 2026. The four rules that each plant’s “Find” reason refers to: (A) the estimate is the confirmed sightings, plus the unconfirmed ones (scaled down where the plant has lookalikes in its genus), plus the sightings marked as planted; (B) the tier by estimate: 1,500 or more is tier 1, 250–1,499 tier 2, 50–249 tier 3, under 50 tier 4; (C) tier 1, Everywhere, also needs a source saying the plant is common in lawns, sidewalks, yards or gardens, vacant lots or towns, or at least one DC street tree of it per km of sidewalk, otherwise it is tier 2; (D) if a reliable source says the plant is rare in this region, or that wild plants rarely bear the harvest, only planted sightings count. iNaturalist is a website and phone app where people post photos of the plants and animals they see. A sighting is “research grade” when other users have confirmed what it is; “needs ID” sightings are not confirmed yet, and “cultivated” ones are marked as planted.

Effort

1 Grab & eat · 2 Quick kitchen prep (under about 30 minutes) · 3 Real work (hours, or cooking needed for safety) · 4 Project (days or equipment). Scored on the simplest worthwhile use; each plant’s page says why.

ID risk

How hard it is to harvest safely. Beginner: no dangerous lookalike, and the edible part is not easily confused with a toxic part. Careful: a toxic lookalike, or toxic parts that end up in the harvest unless removed (for example elderberry stems, unripe ground cherries), or other parts of the plant rated medium-or-higher toxicity, with reliable features to separate them. Expert only: a potentially deadly lookalike that is hard to separate, or (for not-recommended harvests like pokeweed) a plant whose safe preparation can’t be guaranteed. Toxic parts that are obviously separate and thrown away anyway (pits, seeds, skins) don’t raise it; the Toxic parts mark carries that warning.

Native or not, and the invader stars

Origin is where the plant comes from: native, non-native, or mixed (the harvest covers both). The stars rate plants on invasive plant lists: ★★★ Virginia DCR “High” or Maryland prohibited invasive · ★★ Virginia “Medium” · ★ Virginia “Low” · ☆ listed only by the Maryland Invasive Species Council or the Mid-Atlantic Plant Invaders guide (advisory) · no stars: native or not listed.

Seasons

Start, peak and end are given in thirds of a month: early, mid or late. A plant counts as in season for a month if it is in season at any point in that month. Some greens and roots have a second window, in spring or fall; their page shows each window. A season that runs across New Year is shown as one window.

What it looks like

The young fruit of black walnut, a large native tree with long compound leaves of 15 to 23 finely toothed leaflets (NC State). The fruits hang singly or in pairs; each is a round ball with a pointed tip inside a yellow-green husk that does not split (NC State). After the flowers are pollinated, the husk develops first, then the shell, and the seed last (USDA Forest Service). Green walnuts are picked in that early stage, while a knife or needle still passes easily through the whole fruit, and the whole fruit is used, husk and all (Hank Shaw; Backyard Forager). Pickled walnuts are an old English food; Hank Shaw describes them as fairly soft, puckery and strangely floral, a bit like solid steak sauce with a faint bitterness. Steeped in strong alcohol, the green fruits make nocino, a dark walnut liqueur (Backyard Forager).

Safety

The green husk is eaten along with the rest of the young fruit, and it contains juglone, which the USDA Forest Service calls a toxic substance found in walnut leaves, bark, nut husks and roots; black walnut and butternut produce the most juglone of the walnut family (Government of Ontario). The University of Washington Botanic Gardens' library says pickled walnuts, eaten as an occasional snack rather than in large quantities, are no cause for concern, and that anyone sensitive to walnuts should avoid them. Allergy: black walnut is a major tree-nut allergen (FDA). Wear rubber gloves: the juice stains hands for a week or more (Backyard Forager; Hank Shaw), and handling walnut husks has caused blistering skin irritation from juglone that needed a doctor’s care (Cutis, a dermatology journal). Use only sound, fresh fruit: the Government of Ontario warns that walnuts with rotting husks can carry a mold toxin and are not fit to eat. Black walnut’s fruit is a round ball with a pointed tip (NC State). Harmless lookalikes: butternut, whose fruit is oblong, ridged and covered with short sticky hairs; English walnut, a planted tree with only 5 to 11 leaflets; and pecan, which has fewer and longer leaflets than black walnut (NC State). All have edible nuts (NC State), and any walnut can be pickled the same way (Hank Shaw). Kentucky coffeetree, which NC State also lists among trees often confused with black walnut, bears flat reddish-brown or purplish-brown pods up to 10 inches long, nothing like a green walnut; its leaves, seeds and pulp are poisonous (NC State).

Lookalikes

  • Kentucky coffeetree Gymnocladus dioicus toxic

    Not like the green walnut: NC State lists Kentucky coffeetree among trees often confused with black walnut, but its fruits are flat reddish-brown or purplish-brown pods up to 10 inches long, not round green fruits. NC State says its leaves, seeds and pulp are poisonous to livestock, humans and pets.

  • Butternut (white walnut) Juglans cinerea harmless (may be edible)

    NC State lists butternut among trees often confused with black walnut. Butternut’s fruit is oblong to ovoid, with 2 to 4 lengthwise ridges on a green husk covered with short, sticky hairs, and its branch pith is chocolate brown; black walnut’s fruit is globular with a pointed tip, and its pith has buff-colored partitions (NC State). Butternut nuts are edible (NC State). Butternut is on Maryland’s rare-plant list (S2S3), and Virginia keeps it on its watchlist (S3?) (Maryland DNR; Virginia DCR).

  • English walnut (Persian walnut) Juglans regia harmless (may be edible)

    NC State lists English walnut among trees often confused with black walnut. English walnut leaves have 5 to 11 oblong leaflets with mostly smooth edges, against black walnut’s 15 to 23 finely toothed leaflets, and it is a planted tree (NC State). Its nuts are edible (NC State), and pickled English walnuts are a traditional British delicacy (University of Washington Botanic Gardens).

  • Pecan Carya illinoinensis harmless (may be edible)

    NC State lists pecan among trees often confused with black walnut. Black walnut leaves have more leaflets, more ovate and less sharply toothed than pecan’s; pecan has fewer and longer leaflets, and its husk splits into four sections when ripe, while black walnut’s does not split (NC State). Pecan nuts are edible (NC State).

Safety flags

Safety marks and flags: what this means

Deadly lookalike / Toxic lookalike: a cited source names a lookalike of that danger, recorded near DC (an iNaturalist sighting within 25 km, a DC street tree, or a Smithsonian listing for DC) and looking like the part you eat. Other lookalikes are still listed, marked “not recorded near DC” or as not looking like the part you eat. Deadly means a source says eating it may be fatal or calls it deadly, or NC State rates it high severity with life-threatening symptoms (sources sometimes disagree; for example Virginia creeper). Each plant’s Lookalikes list says how to tell them apart; “harmless (may be edible)” lookalikes are listed so you know a mix-up isn’t dangerous. Cook first: cooking is needed for safety (for daylilies it is a precaution, not a sourced requirement). Eat in moderation: a source says to limit quantity or frequency (for example oxalates in sorrels and dock, ginkgotoxin, safrole). Spray risk: a source says the plant is commonly treated with herbicide in parks or lawns (invasive control, lawn weeds) or, for ginkgo, sprayed to stop fruiting. Contamination: a source says the plant concentrates pollutants. Each plant’s Safety flags list gives the details and sources.

ID risk
Beginner
Why
No toxic lookalike is named for the fruit. NC State names butternut, English walnut and pecan among trees often confused with black walnut; all have edible nuts. Black walnut’s fruit is a round ball with a pointed tip, butternut’s is oblong, ridged and sticky-haired, English walnut has only 5 to 11 leaflets, and pecan has fewer, longer leaflets. NC State also lists Kentucky coffeetree, which is poisonous, but that is a whole-tree confusion: its fruits are flat pods, nothing like a round green walnut, so it does not raise the rating.
Handling hazards
Staining hulls (serious)
Soil risk
low
ID risk: what this means

How hard it is to harvest safely. Beginner: no dangerous lookalike, and the edible part is not easily confused with a toxic part. Careful: a toxic lookalike, or toxic parts that end up in the harvest unless removed (for example elderberry stems, unripe ground cherries), or other parts of the plant rated medium-or-higher toxicity, with reliable features to separate them. Expert only: a potentially deadly lookalike that is hard to separate, or (for not-recommended harvests like pokeweed) a plant whose safe preparation can’t be guaranteed. Toxic parts that are obviously separate and thrown away anyway (pits, seeds, skins) don’t raise it; the Toxic parts mark carries that warning.

Handling hazards: what this means

Stings, thorns, irritating or phototoxic sap, staining hulls and spiny husks, with a severity: minor = brief discomfort; moderate = rash or blisters lasting days; serious = burns, scarring or medical care possible.

Soil risk: what this means

Based on the part you eat, following the urban-soil lead guidance on the Field safety page: higher for greens, shoots and roots; moderate for flowers; low for fruit, nuts and sap.

Field safety for every outing (poison ivy, ticks, soil, and more)

When to pick

Starts
early Jun
Peak
mid Jun–late Jun
Ends
early Jul

Pick while a needle or metal skewer passes all the way through the fruit with little or no resistance; once the shell forms inside the husk it is too late (Backyard Forager; Hank Shaw). Black walnut flowers in April and May (NC State), and the husk forms before the shell (USDA Forest Service). In a Missouri study, black walnut shells hardened in early July (University of Missouri and USDA Forest Service). Backyard Forager harvests in northeastern Pennsylvania at the end of June or the start of July and says that, depending on where you live, the walnuts reach the right stage in May or June; the traditional date in England is late June (Hank Shaw). In the DC area green fruits are logged on the trees from mid-May (iNaturalist). No source gives DC dates, so the dates here are estimates: test each tree, because timing shifts from year to year.

How the dates were worked out

Every start, peak and end was re-checked in October 2026. “Sourced” means a source opened during the check states that timing for the DC or Mid-Atlantic area. “Estimated” means no source states it exactly; the reason, the evidence and the source links are under “How the dates were worked out” on each plant’s page. Peaks are often estimated, because few sources name a peak. iNaturalist evidence means research-grade sightings near DC, by month, of the plant at that stage (for example, in fruit). iNaturalist is a website and phone app where people post photos of the plants and animals they see. A sighting is “research grade” when other users have confirmed what it is; “needs ID” sightings are not confirmed yet, and “cultivated” ones are marked as planted.

Season basis: estimated: start, peak, end

Start

estimated: No source dates the start for the DC area. Green fruits are logged on DC trees from mid-May, but they are still small then; early June is placed about three weeks before the late-June dates given for England (Hank Shaw) and northeastern Pennsylvania (Backyard Forager), since DC’s season runs earlier than both.

Peak

estimated: No source gives a DC peak. Mid to late June is the late-June traditional and northeastern Pennsylvania timing moved slightly earlier for DC; it ends before the early-July shell hardening reported in Missouri.

End

estimated: The Missouri study site (Windsor, Missouri) is the only dated source on shell hardening; DC is assumed to be similar, so early July is the end, with the needle test deciding for each tree.

Evidence

start: NC State: 'Flowers from April to May and are wind pollinated.' University of Missouri and USDA Forest Service (Missouri): pistillate bloom in late April to early May, and fertilization is 'followed by a period of rapid expansion of the fruit'. Backyard Forager: 'Depending on where you live, the walnuts will be at the right stage in May or June.' iNaturalist (25 km of DC, research grade, fruiting annotation): 1 in week 20, 2 in week 21, 3 in week 22, 3 in week 23, 4 in week 24. | peak: Hank Shaw: 'the traditional harvest date in England is late June'. Backyard Forager (author’s reply): 'I usually harvest in NE PA at the end of June, beginning of July.' iNaturalist DC fruiting records: weeks 22-24 (3, 3, 4) and 26-27 (3, 8). | end: University of Missouri and USDA Forest Service: 'In early July, shell hardening occurs and the embryo and cotyledons enlarge.' Backyard Forager: 'If you can push it through the entire nut with little or no resistance, you’re good to go.' Hank Shaw: 'Once that shell forms inside the walnut’s hull, you’re too late'.

Where to look

The same trees as the fall nut harvest, along stream valleys, floodplain edges and trailsides; logged most in Rock Creek Park, on the C&O Canal towpath and along Four Mile Run. Green walnuts are ambiguous on the C&O Canal, at the listed National Capital Parks-East sites, in Prince William Forest Park and in Virginia state parks (ask the park first); Rock Creek Park, the Four Mile Run parks and the other places logged most are look-only. Otherwise pick from private trees with the owner’s permission.

Habitats
street & yard trees (planted), woods edges, trailsides & thickets, floodplain & stream-valley forest
Habitats: what this means

Listed where the plant’s own sources place it in that habitat. “Disturbed ground & waste places” means a cited source places it on disturbed areas, sites, soil or ground, on waste places or waste ground, on construction or abandoned building sites (old home sites count), on rubble or in strip mines. When the source gives examples of the disturbed places, at least one example must be of that kind. Examples that do not count: natural or forestry disturbance (treefall gaps, fire, windthrow, flood scour, old riverbanks and creeks, clear-cuts); roadsides, railroads and rights-of-way; and abandoned fields, pastures and farmland, which are “Old fields & meadows”. “Vacant lots” only where a source says vacant or empty lots.

Most-logged places

None of the most-logged places allows picking.

Ask first: rules unclear or not checked

  • C&O Canal NHP (towpath, Georgetown to Great Falls MD and beyond)

    40 sightings · Legal to pick: ambiguous · see them on iNaturalist

    Ambiguous: the C&O compendium allows walnuts (1 bushel per person per day) but does not say whether unripe green walnuts picked from the tree count; ask the park first. Of these, 3 are at Carderock.

No picking here (4 places)
  • Rock Creek Park

    44 sightings · Legal to pick: no · see them on iNaturalist

    Look but don’t pick: Rock Creek Park’s compendium bans gathering any fruit, nut, berry, seed or greenery.

  • Four Mile Run stream valley (Arlington/Alexandria)

    39 sightings · Legal to pick: no · see them on iNaturalist

    Look but don’t pick: Arlington County park rules (flora shall not be removed or disturbed) and Alexandria’s permit rule both apply.

  • Rock Creek Regional Park (MD)

    20 sightings · Legal to pick: no · see them on iNaturalist

    Look but don’t pick: Montgomery/Prince George’s parks (M-NCPPC) ban harvesting vegetation without a permit.

  • Mount Vernon Trail

    19 sightings · Legal to pick: no · see them on iNaturalist

    Look but don’t pick: GW Memorial Parkway sites (incl. Great Falls VA, Theodore Roosevelt Island, Dyke Marsh) designate nothing for gathering.

Most-logged places: what this means

The places with the most research-grade iNaturalist sightings within 25 km of downtown DC (re-counted in October 2026 over every named place, campuses, condominiums and private grounds included), each marked legal to pick or not. A sighting inside several named places counts once, for the smallest of them, but a sighting inside a National Park Service park never counts for a private, campus or unchecked place. iNaturalist shows where people walk and log plants, not true abundance. Private campuses, condominiums, museums, estates and utility land (Pepco’s power-line land near Sligo Creek) are marked “no” (pick only with the owner’s permission); public university campuses, city parks and other places whose picking rules were not checked (county stormwater land, the U.S. Capitol Grounds, Greenbelt’s North Woods, federal facilities such as the National Zoo) are “unknown”. A place needs at least 2 sightings, so plants with very few sightings have no places. At-risk plants (butternut, nannyberry, American chestnut, ramps, riverbank goldenrod) get places like every other plant; each page says why the plant is at risk and gives any advice its sources give. For some places, mostly Rock Creek Park, the iNaturalist map shows more sightings than the count here, because a map link cannot leave out exactly the sightings credited to another place. iNaturalist is a website and phone app where people post photos of the plants and animals they see. A sighting is “research grade” when other users have confirmed what it is; “needs ID” sightings are not confirmed yet, and “cultivated” ones are marked as planted.

Ways to use it

  • pickled walnuts: prick the whole green fruits, brine them for 8 days, leave them a day in the sun until they turn black, then pack them in jars under a hot pickling liquid and wait at least a month (Hank Shaw)
  • serve pickled walnuts with cheese and cold meats, as in an English ploughman’s lunch, or add them to beef or lamb stews (Hank Shaw)
  • nocino, a dark walnut liqueur: steep the quartered green fruits in high-proof alcohol for 40 days, strain, sweeten and let it age for months (Backyard Forager)
  • harvest only while a needle or metal skewer passes all the way through the fruit with little or no resistance; once the shell has formed inside, it is too late (Backyard Forager; Hank Shaw)
  • harvest and cut the fruits wearing rubber gloves: the juice stains hands for a week or more (Backyard Forager; Hank Shaw)

Keeping

Start the brine or the infusion soon after picking, using only fresh, firm fruit; keep the finished pickles in the refrigerator.

Use within
within a few days
Keeps fresh
Fresh green walnuts are not kept: start the brine or the infusion soon after picking, and use only fresh, firm fruit free of spoilage (general guidance for pickles, NCHFP). Hank Shaw’s pickled walnuts, kept cool, last a year.
Canning
no tested recipe: refrigerate or freeze, don’t can
Keeping basis
general guidance for its type

Ways to keep it

  • Infuse as researched: infuse/vinegar; canning: n/a (not shelf-canned)

    Nocino: steep the quartered fruits in high-proof alcohol for 40 days in a cool, dark place, strain, mix with an equal amount of sugar syrup, let it sit three months and bottle it; the flavor improves over the next six months (Backyard Forager).

  • Pickle as researched: pickle; canning: no tested recipe — refrigerator pickle only

    Hank Shaw brines the pricked fruits for 8 days, sun-dries them a day until black, packs them under a hot pickling liquid and keeps the jars below 70°F, in the fridge or a basement, for at least a month before eating. No tested home-canning recipe for pickled walnuts was found, and NCHFP says to use only recipes with tested proportions of ingredients, so keep the jars in the refrigerator.

Canning: what this means

Shelf-stable canning, three levels. Lab-tested: a lab-tested recipe from the National Center for Home Food Preservation (NCHFP) or Oregon State covers this fruit and product, or a generic recipe for its kind (the line says so, for example chokeberry). Extension recipe: a published Extension recipe (University of Alaska Fairbanks, written for Alaska species; University of Maine’s dandelion jelly), or a process that is safe only with a pH meter; follow it exactly, never improvise. No tested recipe: refrigerate or freeze, don’t can. “Hot-bottled syrup” = maple and walnut syrup, which keep when bottled hot at full syrup density. The Canning line names the exact product each source covers, for example “whole berries” or “juice”; a product not named there (such as juice from a berry with only a whole-berry recipe) has no tested recipe.

Keeping basis: what this means

“Specific to this plant” or “general guidance for its type” (for example NCHFP guidance for leafy greens applied to a wild green).

Nutrition

Not researched: in October 2026, only the calendar’s plants of the month and chicory leaves were researched.

Native or not

Origin
native
Native range
eastern & central United States
Virginia invasive rank
not listed
Maryland invasive status
not listed
Native or not, and the invader stars: what this means

Origin is where the plant comes from: native, non-native, or mixed (the harvest covers both). The stars rate plants on invasive plant lists: ★★★ Virginia DCR “High” or Maryland prohibited invasive · ★★ Virginia “Medium” · ★ Virginia “Low” · ☆ listed only by the Maryland Invasive Species Council or the Mid-Atlantic Plant Invaders guide (advisory) · no stars: native or not listed.

Virginia DCR, Virginia Invasive Plant Species List (effective September 2024), verbatim: "Under the DCR Invasive Species Assessment Protocol, approved by the Virginia Invasive Species Working Group, January 2024, species were ranked as exhibiting high, medium or low levels of invasiveness based on their threat to natural communities and native species. Invasiveness rank is higher for species that: • Alter ecosystem processes, such as succession, hydrology or fire regime. • Are capable of invading undisturbed natural communities. • Cause substantial impacts on rare or vulnerable species or natural communities or high-quality examples of more common communities. • Are found widely distributed and generally abundant where present. • Disperse readily to new areas. • Are difficult to control." The list also states: "The list is for educational purposes only and has no regulatory authority."

Maryland Department of Agriculture, Maryland Prohibited Invasive Plant Law and Regulations page, verbatim: "Plants on the Maryland Prohibited Invasive Plant List may not be added to stock after the effective date and should not be sold after their phase-out period ends."

No official DC invasive plant list was found.

How the ratings were set

Find
Common in the right habitat Estimate 2,516 = 1,184 research-grade iNaturalist sightings within 25 km + 1,282 needs-ID sightings counted at 98% (1,184 of the 1,206 research-grade Juglans sightings here are black walnut) + 73 'cultivated' (planted) sightings (rule A); that is tier 1 by count (rule B). Rule C: none of its sources says it is common in, or a weed of, an everyday place (lawns, sidewalks, yards or gardens, vacant lots, towns), and DC’s street-tree inventory lists 248 living black walnuts, under the line of one per km of DC sidewalk (2,406), so it cannot be tier 1 (Everywhere). Final tier 2.
Effort
Quick kitchen prep Test each fruit with a needle, then glove up and prick the fruits for brine (about 30 minutes of work) or quarter them into alcohol; the rest is waiting: 8 days in brine and a month in the jar for pickles (Hank Shaw), or 40 days of steeping for nocino (Backyard Forager).
Find: what this means

1 Everywhere · 2 Common in the right habitat · 3 Patchy · 4 Elusive. This is about how much there is, not whether you may pick it. It is based on iNaturalist sightings within 25 km (about 15 miles) of downtown DC, counted on October 3, 2026. The four rules that each plant’s “Find” reason refers to: (A) the estimate is the confirmed sightings, plus the unconfirmed ones (scaled down where the plant has lookalikes in its genus), plus the sightings marked as planted; (B) the tier by estimate: 1,500 or more is tier 1, 250–1,499 tier 2, 50–249 tier 3, under 50 tier 4; (C) tier 1, Everywhere, also needs a source saying the plant is common in lawns, sidewalks, yards or gardens, vacant lots or towns, or at least one DC street tree of it per km of sidewalk, otherwise it is tier 2; (D) if a reliable source says the plant is rare in this region, or that wild plants rarely bear the harvest, only planted sightings count. iNaturalist is a website and phone app where people post photos of the plants and animals they see. A sighting is “research grade” when other users have confirmed what it is; “needs ID” sightings are not confirmed yet, and “cultivated” ones are marked as planted.

Effort: what this means

1 Grab & eat · 2 Quick kitchen prep (under about 30 minutes) · 3 Real work (hours, or cooking needed for safety) · 4 Project (days or equipment). Scored on the simplest worthwhile use; each plant’s page says why.

Sources

34 sources, each linked to the original.

  1. Rock Creek Park Superintendent’s Compendium (2026) National Park ServiceBacks up: picking rules
  2. C&O Canal NHP Superintendent’s Compendium, effective September 11, 2026 National Park Service, Chesapeake and Ohio Canal NHPBacks up: picking rules
  3. National Capital Parks-East 2026 Superintendent’s Compendium National Park ServiceBacks up: picking rules
  4. Prince William Forest Park Superintendent’s Compendium National Park Service, Prince William Forest ParkBacks up: picking rules
  5. 4VAC5-30-50. Flowers, plants, minerals, etc. Virginia Law Library (law.lis.virginia.gov)Backs up: picking rules
  6. 36 CFR 2.1 - Preservation of natural, cultural and archeological resources Legal Information Institute, Cornell Law School (text of federal regulation)Backs up: picking rules
  7. Maryland man fined $50 for picking berries ReasonBacks up: picking rules
  8. List of Rare, Threatened, and Endangered Plants of Maryland (March 2026) Maryland Department of Natural Resources, Wildlife and Heritage ServiceBacks up: picking rules, safety details
  9. Natural Heritage Resources of Virginia: Rare Plants (September 2026) Virginia Department of Conservation and Recreation, Division of Natural HeritageBacks up: picking rules, safety details
  10. Juglans nigra (Black Walnut) NC State Extension Gardener Plant ToolboxBacks up: description, habitat, season, safety
  11. Black walnut (Silvics of North America) USDA Forest ServiceBacks up: description, habitat, season, safety, safety details
  12. Pickled Walnuts (Hank Shaw, 2014, updated 2022) Hunter Angler Gardener Cook (Hank Shaw)Backs up: description, uses, season, safety, storage, keeping
  13. Foraged Nocino: a Delicious Liqueur Made from Unripe Nuts (Ellen Zachos, 2018) Backyard ForagerBacks up: description, uses, season, safety, storage, keeping
  14. iNaturalist research-grade observations of Juglans nigra within 25 km of downtown DC iNaturalistBacks up: findability
  15. Annotated Checklist of the Vascular Plants of the Washington-Baltimore Area, Part I (Shetler & Orli, 2000) Smithsonian Institution, National Museum of Natural History, Department of BotanyBacks up: habitat
  16. Maryland Forest Service Seeks Black Walnuts Maryland Department of Natural ResourcesBacks up: habitat
  17. DC street-tree inventory (DDOT Urban Forestry, UFA Street Trees layer): living trees by species, queried 2026-10-05 (248 living black walnuts) District of Columbia (DDOT Urban Forestry Division, via DC GIS)Backs up: habitat, findability
  18. USDA PLANTS Database: Juglans nigra (JUNI), native status USDA NRCSBacks up: native or invasive status
  19. Virginia Invasive Plant Species List (effective date: September 2024) Virginia Department of Conservation and Recreation, Division of Natural HeritageBacks up: native or invasive status
  20. Maryland Prohibited Invasive Plant Law and Regulations (Maryland Prohibited Invasive Plant List, updated January 2026; additions effective July 15, 2026; 'Next Plants To Be Assessed' 2026-2027) Maryland Department of Agriculture, Plant Protection & Weed ManagementBacks up: native or invasive status
  21. Non-Native Invasive Terrestrial Plant Species in the State of Maryland (updates approved through the April 18, 2024 MISC meeting) Maryland Invasive Species CouncilBacks up: native or invasive status
  22. Plant Invaders of Mid-Atlantic Natural Areas, Field Guide (Swearingen & Fulton, 2022; successor to the NPS/USFWS 5th ed., 2017) Mid-Atlantic Invasive Plant Council / Passiflora Press (hosted by Bugwood/Mid-Atlantic Invaders Tool)Backs up: native or invasive status
  23. Invasive Plants in the District DC Department of Energy & EnvironmentBacks up: native or invasive status
  24. Questions and Answers Regarding Food Allergen Labeling (Edition 5): Guidance for Industry, January 2025 U.S. Food and Drug AdministrationBacks up: safety
  25. Juglans cinerea (Butternut) NC State Extension Gardener Plant ToolboxBacks up: safety, picking rules, safety details
  26. On the safety of pickled walnuts (Plant Answer Line) University of Washington Botanic Gardens, Elisabeth C. Miller LibraryBacks up: safety, safety details
  27. Walnut toxicity Government of Ontario (Ministry of Agriculture, Food and Rural Affairs content)Backs up: safety, safety details
  28. Discoloration and Bullous Lesions on the Hands (Photo Challenge; Cutis 104(4), October 2019) Cutis (peer-reviewed dermatology journal)Backs up: safety, safety details
  29. Juglans regia (English Walnut) NC State Extension Gardener Plant ToolboxBacks up: safety, safety details
  30. Carya illinoinensis (Hardy Pecan, Pecan) NC State Extension Gardener Plant ToolboxBacks up: safety, safety details
  31. Gymnocladus dioicus (Kentucky Coffeetree) NC State Extension Gardener Plant ToolboxBacks up: safety, safety details
  32. Ambered Kernels in Stenospermocarpic Fruit of Eastern Black Walnut (Warmund and Van Sambeek, HortScience 49(9), 2014) University of Missouri and USDA Forest Service, Northern Research StationBacks up: season
  33. iNaturalist week-of-year histogram of research-grade black walnut observations annotated 'fruiting' within 25 km of downtown DC iNaturalistBacks up: season
  34. General Information on Pickling National Center for Home Food Preservation (University of Georgia)Backs up: storage, keeping