Black walnut (Juglans nigra) is one of our most valuable native trees.  Its wood has long been used for cabinetry, wall paneling, gunstocks, furniture and specialty items.  The heartwood has a beautiful dark brown to purplish color and is straight-grained and hard.  Walnuts are also sought after for food by both humans and some animals. Connecticut is on the edge of the native range of black walnut but it does well planted as a landscape tree on suitable sites. 

Several distinctive features can be used to identify black walnut.  At maturity, it is a large tree with an open crown, attaining a height of 70-90’ and a diameter of 2-4’.  The  12-24” long leaves are compound with 9-21 leaflets that are 2 ½ -5” long and finely toothed on the edges.  The leaflets are stalkless and are finely haired on the upper surface, soft hairs on the lower.  Fall color is yellow.  The bark is dark brown and deeply furrowed in scaly ridges that often form a diamond like pattern.  More info on the characteristics of black walnut and its best site characteristics is available at the UConn Plant Database website.

In addition to its lumber and nuts, the bark of the black walnut tree has been used for tanning and a yellowish brown dye can be made from the husks of the nuts.  Bruised nut husks were once used to kill fish for food but this is now illegal.  Walnut leaves, bark, nut husks and roots contain a toxic substance called juglone.  Bark, nut husks and roots contain the highest amounts, and it is secreted into the soil from both living and dead roots.  Plants sensitive to juglone will show symptoms ranging from poor growth to death if grown under the canopy or in the root zone of a black walnut.  Highly sensitive plants, such as tomatoes, will show sensitivity to the very small quantity of juglone when grown near a black walnut.  One solution if a garden will be located near a black walnut is to plant in raised beds.  This will significantly reduce the likelihood of toxicity.  More information, including lists of sensitive and tolerant plants, is available here.

If you have a black walnut tree that is large enough to bear nuts, you might be interested in information on harvesting, cracking and storing them.  You can harvest walnuts either before or after they fall to the ground, but you’re more likely to beat the squirrels to them if you harvest them from the tree!  Nuts are ripe in the fall, September to October.  Check for ripeness by pressing on the hull with your thumb.  When you can dent it with pressure, it is ready to pick.  The juice in the hulls stains easily so gloves should be worn when removing them.  Work on a surface that can be stained or that is protected.  Hulls can be removed with a hammer or other tools.  Remaining hull debris can be removed by washing in water.  At this stage, nuts that float can be discarded; they are not full.  Save the ones that sink.  After washing, dry nuts in a cool, well-ventilated area for 2-3 weeks.  For more information on harvesting, cracking and storing your walnuts, click here.

Shells are usually cracked using a nutcracker or a hammer.  If using a hammer, place the nut pointed end up and strike it until it splits.  To reduce shattering of the nutmeats, soak the nuts in their shells for 1-2 hours before cracking.  Even the shells of the black walnut have many uses, primarily as an abrasive in cleaning products or processes.  During World War II, ground shells in a “nut shell” blaster were used to clean airplane pistons.  This practice was then adopted by the auto industry and used to deburr gear components.  Ground nut shells are also used in drilling mud for oil drilling, filler in dynamite, paint stripping propellant and as a flour-like carrying agent in some insecticides. 

J Allen

For more information, contact the UConn Home & Garden Education Center toll free in CT at (877)486-6271 or by email at ladybug@uconn.edu.