I’m in the San Fran bay Area (Marin County). We have a lot of Walnut Trees planted here. Many up and down neighborhood streets. Walnut trees tend to grow only so high, then no higher. They have beautiful purple blossoms in the spring. The blossoms look a lot like Wisteria for a few weeks.
The Walnuts will also do a lot of color shifting in late autumn as in right now. I see several Walnut Trees ablaze in scarlet, yellow ochre and tangerine. For a deeper red, there is always one version of the Japanese Maple to rely on. The Maple foliage becomes the color of Merlot wine and stays that way for months.
What type of walnut trees do you have? We have black walnuts and butternut trees. They are native and were here when we bought the lots.
We tried to plant various others in the front yard, but none of them were ever able to survive - the front yard’s soil is particularly bad.