I've had two emails this week asking about Ceanothus and yellow leaves.
They will often turn yellow and drop leaves in spring as they push new growth. If you over water, fertilize or get too much rain they'll show more yellow leaves.
We've only had tons of dry, yellow leaves on very wet years. 50 inches of rainfall makes Ceanothus kind of melt.
We've also commonly seen tons of yellow leaves on plants that are on drip irrigation, amended soil, or fertilized. Sometimes just before they die.
I had a hard time finding yellow leaves on our Ceanothus in the ground as we do not water and it was a dry year.