From this time of summer and on into fall, you might just start seeing black walnuts. Yes, this is why we have black walnut ice cream — our US and Canadian forefathers ate more black walnuts than we do. The trees are native to North America, grow down south and way up north as well as out west. They are both pretty and hardy and were often used to make fencelines; they used to be popular as yard trees but now are disfavored because of the nut mess. They are edible and yummy, but a bit difficult to deal with, if you start from scratch. This is why squirrels now usually get them instead.
First, they have a giant green hull that will stain your hands black. (If the green hull has turned black, it’s easier to open, but the squirrels usually will grab it from you.) So you have to get through that, and apparently everyone has their own methods.
Then, inside the hull, you have a nutshell, which is more like what you see with walnuts in the store. (Store walnuts are usually English walnuts, which are brown/tan and not black.) However, black walnuts are spikier and tougher than English walnuts. This usually has to be put up for several weeks in order to “cure” and get nice and dry. Then you can crack it, which usually involves things like hammers, vises, or driving over a bag of them with a car.
Once you get to the kernel, this is the part you get to eat.
Here’s the commercial side of black walnuts, which apparently is mostly pursued in the Ozarks and the South.