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A Forager’s Year

No. 62

Black walnut

Juglans nigra

Nut & seed nuts

Drawing: Britton & Brown, Illustrated Flora (1913)

Find
Common in the right habitat
Effort
Real work
ID risk
Beginner
Origin
native
Uses
  • Baking & desserts
  • Roasted nuts

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

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

A large native tree with long compound leaves. It drops large, round, green-husked nuts, often after the leaves have fallen. Inside the thick husk is a very hard, furrowed shell. The kernel has a strong, rich, distinctive flavor, quite unlike store-bought English walnuts.

Safety

The husk juice stains skin, clothing and concrete almost permanently and can irritate sensitive skin, so wear gloves. Discard moldy or floating nuts. Oregon State lists mold, rancidity and pantry moths as the main storage losses. Juglone in the husks, roots and leaves is toxic to many nearby plants, so don’t compost husks onto garden beds. Allergy: black walnut is still a major tree-nut allergen under FDA’s 2025 guidance.

Safety flags

Safety marks and flags: what this means

Deadly lookalike / Toxic lookalike: a cited source names a lookalike of that danger. 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 nut is named in the sources.
Handling hazards
Staining hulls (minor)
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
mid Sep
Peak
late Sep–early Oct
Ends
mid Nov

Black walnuts ripen from mid to late September (Virginia DWR; Iowa State Extension) and are ready when the husk dents under thumb pressure (Iowa State). Along the Route 1 corridor the main harvest runs from late September to early October, with good nuts still falling into early November (Hyattsville Wire). Many drop after the leaves fall (Silvics Manual; Maryland DNR). The mid-November end is an estimate. Good crops come irregularly, about twice in five years (Silvics Manual).

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, end

Start

estimated: The month is sourced; 'mid' comes from Iowa and southwest Virginia, not the DC area.

Peak

sourced

End

estimated: No source gives a closing date; mid November reflects the early-November local report and the iNat tail.

Evidence

start: Virginia DOF: matures September to October. Iowa State: mid to late September (Iowa). Virginia DWR (southwest Virginia mountains) lists black walnuts as ripening about the same time as pawpaws, in mid to late September. | peak: Hyattsville Wire (Route 1 corridor, Prince George’s Co., MD): 'harvesting season is typically late September to early October'. Maryland DNR’s 2019 walnut collection ran from late September to Oct 26. | end: Hyattsville Wire, 4 Nov 2021: a forager was collecting recently fallen walnuts on the Paint Branch Trail the week before, and good fallen nuts were still there. Penn State Extension (Lehigh Co., PA): collect wild walnuts in October and November. Silvics: nuts drop shortly after the leaves fall. DC iNat fruiting records continue to week 46 (mid-Nov), with one in week 48.

Where to look

Stream valleys, floodplain edges and trailsides; legal on the C&O Canal (1 bushel/day) and at NACE sites such as Piscataway and Fort Washington parks, while the trees along Four Mile Run and in Rock Creek Park are look-only.

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

You may pick here

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

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

    Legal to pick under the C&O Canal compendium (by hand, personal use, daily limit; trail-side only at Great Falls MD). 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 (rugosa rose) have no places. No most-logged places are named for at-risk plants (ramps, chinquapin, American chestnut); chinquapin’s page names Mason Neck State Park, where picking is legal, and asks you to leave most nuts. 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

  • Hull soon after gathering, wearing rubber gloves, because the husk juice darkens the kernel and makes it strong-tasting if left on (Iowa State Extension)
  • Wash the hulled nuts and discard floaters, which are unfilled (Iowa State Extension)
  • Cure 2-3 weeks on screens in a shed or garage (Iowa State); dry until the divider between the halves snaps (Oregon State Extension)
  • Soak 1-2 hours before cracking with a hammer on the pointed end to reduce shattering, then freeze the kernels, which keep almost indefinitely (Iowa State Extension)
  • Use in brownies, ice cream and other desserts (Hyattsville Wire); roasting is optional but improves flavor (Oregon State Extension)

Keeping

Hull within a day of gathering, cure 2-3 weeks on screens, then store in the shell cool and dry, or crack and freeze the kernels (they keep almost indefinitely).

Use within
months+
Keeps fresh
Hull right after harvest; husk juice left on darkens the kernel and makes it strong-tasting. Wash, discard floaters, then cure on screens in a cool, dry, ventilated shed or garage for 2-3 weeks (Iowa State) until the divider between the halves snaps (OSU). Cured in-shell nuts keep up to about a year refrigerated, 2 years frozen at 0°F, or for less time at 55°F or cooler in a closed container (general guidance for walnuts, OSU).
Keeping basis
specific to this plant

Ways to keep it

  • Dry as researched: roast & store; canning: n/a (not shelf-canned)

    Roasting is optional; roasted nuts keep only a few months (OSU).

  • Freeze as researched: freeze; canning: n/a (not shelf-canned)

    Freeze the picked-out kernels in plastic bags; they keep 'almost indefinitely' frozen, and only for short periods in the fridge (Iowa State).

  • Store whole as researched: store in shell; canning: n/a (not shelf-canned)

    After curing, store in closed containers, cool and dry, or refrigerate; this keeps meal moths out (OSU).

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
Real work Hull right away wearing rubber gloves, wash, cure 2-3 weeks, soak 1-2 hours, then crack with a hammer and pick out the kernels.
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

23 sources, each linked to the original.

  1. Rock Creek Park Superintendent’s Compendium (2026) National Park ServiceBacks up: picking rules
  2. 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
  3. Maryland man fined $50 for picking berries ReasonBacks up: picking rules
  4. Black Walnuts: Nutritious Native Nut Worth Cracking Edible JerseyBacks up: description, uses
  5. Explaining Black Walnuts America’s Test Kitchen (Cook’s Illustrated)Backs up: description, uses
  6. 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: findability
  7. iNaturalist research-grade observations of Juglans nigra within 25 km of downtown DC iNaturalistBacks up: findability
  8. Maryland Forest Service Seeks Black Walnuts Maryland Department of Natural ResourcesBacks up: habitat, season, description
  9. The Sweet Side of Harvesting Black Walnuts on Route 1 (Nov 4, 2021) Hyattsville WireBacks up: habitat, season, uses, description
  10. USDA PLANTS Database: Juglans nigra (JUNI), native status USDA NRCSBacks up: native or invasive status
  11. Virginia Invasive Plant Species List (effective date: September 2024) Virginia Department of Conservation and Recreation, Division of Natural HeritageBacks up: native or invasive status
  12. 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
  13. 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
  14. 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
  15. Invasive Plants in the District DC Department of Energy & EnvironmentBacks up: native or invasive status
  16. FDA finalizes two guidance documents related to food allergens (Jan 2025) Covington & Burling LLP (summary of FDA guidance)Backs up: safety
  17. Free Fall Food for the Asking: Locavore Living (Bruce Ingram, Sept 2018) Virginia Department of Wildlife ResourcesBacks up: season
  18. Growing Green: native nut tree species to be enjoyed (Sept 2024) Penn State Extension, Lehigh County (column in Lehigh Valley Press)Backs up: season
  19. Juglans, walnut (Woody Plant Seed Manual, Agriculture Handbook 727) USDA Forest ServiceBacks up: season
  20. Acorn and Nut Identification Guide (Forestry Topic 60, Sept 2026) Virginia Department of ForestryBacks up: season, description
  21. Black walnut (Silvics of North America) USDA Forest ServiceBacks up: season, habitat, safety, description
  22. How to Harvest, Crack, and Store Black Walnuts Iowa State University Extension and OutreachBacks up: uses, safety, season, storage, keeping
  23. Harvesting, Handling, and Storing Nuts from the Home Orchard (FS 146, rev. 2013) Oregon State University Extension Service (PDF hosted by UC ANR)Backs up: uses, safety, storage, keeping