Ceanothus divergens, commonly known as Calistoga ceanothus, is an evergreen shrub native to the chaparral and woodlands of the Northern California Coast Ranges, especially in Napa County around Calistoga. It thrives at altitudes below 1,640 feet (500 meters) on rocky, volcanic slopes. This species typically reaches 3 to 6 feet (1 to 2 meters) in height and width, with a dense, rounded form. The foliage is small and dark green, providing a lush backdrop for the profuse clusters of tiny, fragrant blue or purple flowers that bloom in spring, from April to May. The flowers are highly attractive to pollinators, and the plant produces small, sub-globose fruits that are less conspicuous.

Calistoga ceanothus is valued for its drought tolerance and ability to stabilize slopes, making it an excellent choice for erosion control in dry, challenging sites. It is also used in native plant gardens, as a low-maintenance ground cover, or for natural landscaping. This shrub prefers full sun to partial shade and is adapted to well-drained soils; it does not tolerate waterlogged conditions. While it is generally disease-resistant, it can be susceptible to root rot if overwatered. Calistoga ceanothus is also a fire-adapted species, regenerating after wildfires, which are a natural part of its ecosystem.CC BY-SA 4.0