Black Walnuts

Black walnut in shell, found in Frick Park, 19 Nov 2023 (photo by Kate St. John)

22 November 2023

The Nutty Series: Black walnut

Black walnut trees (Julgans nigra) are common in the Pittsburgh area. Their nuts are always ready to eat in time for the holidays.

In September the fruit was still on the trees while we searched for fall warblers among the leaves.

Black walnut leaves and fruit (photo from Wikimedia Commons)

By the end of October the fruit had fallen and started to look bruised. Eventually the husks turned black.

Black walnut in husk, 23 Oct 2023 (photo by Kate St. John)

But most black walnuts aren’t abandoned that long. Squirrels gather them for winter food and eat a few along the way.

Fox squirrel opening a black walnut (photo by Donna Foyle)
Fox squirrel opening a black walnut (photo by Donna Foyle)

Squirrels know that they have to open the shell on both sides to get all of the nut meat.

Black walnut shell opened by a squirrel (photos by Kate St. John)

The meat does not come out easily! It usually breaks into small pieces on the way out and is never the perfect shape of grocery store walnuts.

Black walnut shell and meat (photo from Wikimedia Commons)

The ones we buy in the grocery store that are grown in California are English walnuts (Juglans regia) which would not be possible without the life-giving participation of black walnut trees (Julgans nigra).

(English) Walnut pie (photo from Wikimedia Commons)

Non-native English walnuts are susceptible to root diseases in California so walnut farmers plant native black walnut trees to start the orchard. When the black walnuts are a year old with strong roots and vigorous base they are chopped off and an English walnut shoot is grafted to the stump.

All the trees in the orchard below show the wider stump base (highlighted in yellow) that ends at the graft point. Above the graft English walnuts produce their own delicious nuts which are harvested after they fall by sweeping and vacuuming from the ground. FLORY harvesting equipment is pictured below.

Walnut orchard in California with FLORY sweeper machine (photo from Wikimedia Commons) The trunk and treetops are Juglans regia, the stump and roots are Juglans nigra
vacuuming up walnuts in the orchard, video from Midland Tractor on YouTube

Black walnut trees can be identified in winter as a bare tree standing alone with twigs that have alternate (not opposite) small buds above large leaf scars.

Black walnut trees tend to stand alone (photo from Wikimedia Commons)
Black walnut buds and leaf scar, Schenley Park, 27 Feb 2023 (photo by Kate St. John)

Black walnut trees stand alone because …

Like other walnuts, the roots, inner bark, nut husks, and leaves [of Julgans nigra] contain a nontoxic chemical called hydrojuglone; when exposed to air or soil compounds it is oxidized into juglone that is biologically active and acts as a respiratory inhibitor to some plants. Juglone is poorly soluble in water and does not move far in the soil and will stay most concentrated in the soil directly beneath the tree.

Symptoms of juglone poisoning include foliar yellowing and wilting. A number of plants are particularly sensitive. Apples, tomatoes, pines, and birch are poisoned by juglone, and as a precaution, should not be planted in proximity to a black walnut.

quote from Wikipedia

(credits are in the captions)

12 thoughts on “Black Walnuts

  1. Years ago we had a farm on Rt 910. There were several younger Black Walnut trees and one huge one. This large tree was about 75 ft tall and just as wide. No trees or shrubs grew within its drip line and a wider perimeter.

    1. Not easily, i use a screw type nut crusher, but i think I’ll donate the rest to the squirrels

  2. Is black walnut root highly toxic to touch give you hard breathing if you sand it and breathe the dust? I heard they made gun stocks out of it?

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