Walnuts are hell on other plant life. I have a couple black walnut trees on the edge of my lawn, and I have had to experiment a bunch to see what vegetables I can actually get to grow in my garden...
Given what the parent commenter has said about having to experiment with different plants, it stands to reason that they have a healthy black walnut tree in their garden rather than a regia.
Very mediocre results with my tomatoes and cucumbers this year, but it was very, very dry.
Oh, and zucchini. But you can almost plant zucchini on asphalt and it would find a way to produce bushels of the stuff...