It has been in cultivation for several thousands of years. Throughout that time, it escaped cultivation to naturalize in many regions between the Balkans and the Himalayas. It most likely originated from a much smaller natural range within Persia. An interesting certainty of its dubious original range is that English walnut, Juglans regia, is not actually English.
English walnut likely arrived at Spanish Missions of California prior to 1800. It became a major agricultural commodity of both the Sacramento Valley and the San Joaquin Valley. A few old trees survive within urban areas that were formerly orchards of the Santa Clara Valley. Newer trees are unfortunately rare within home gardens because they get messy.
English walnut trees rarely grow more than forty feet high and wide here. Their abundant foliar, floral and fruit debris is toxic to young plants though, and stains hardscapes. Each type of debris sheds during a different season. Squirrels might claim most or all nuts, but drop shredded hulls. The deciduous and pinnately compound leaves can be a foot long.
Tony Tomeo 
Our black walnuts here drive the squirrels wild when they are formed. There is big activity to collect all of them. And they hide them in some really ridiculous places, like on a windowsill.
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Do you know the species of the black walnut? They can be so . . . vague. I mean, there are a few species that are known as black walnut. I only recently learned that the Southern California black walnut is a separate species from the black walnut that grows south of here. I thought that it was just sucker growth from stumps of the common sort that got cut down or fell down. It actually grows like that naturally, and does not get big.
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No, all black walnut trees here are called black walnut. They are all over this area, so they are also………..vague.
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It’s so sad when a lovely tree gets a bad reputation. I do like black and English walnuts. And picking them on a winter evening is as good as knitting is supposed to be…
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Bad reputation? I know that they can be messy and unhealthy for plants below them, but they work nicely in some unlandscaped areas. California black walnuts flank some of the old roads near here, and bother no one with their toxic mess. In fact, their suppression of weeds might be an asset. I intend to grow English walnut again, because it is so familiar.
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