Shade is an important commodity in many parts of California. You can make a beautiful drought tolerant, fire resistant, garden. With very little water you can greatly improve the health of your mature oak trees by planting native understory plants. You can have a lush green garden in summer with a few minutes of water sprinkled on the foliage once a week or two.! Water the foliage, not the ground. Your oak trees and the wild life will thank you.
In our demonstration garden these plants occur under
mature oaks which
can not handle garden water. Do not most water under California native
during the summer after first summer.. If more than the mulch gets
watered you put the tree
at risk (unless it normally grows in creeks).
Get rid of the weeds! Invasive grasses, yellow star thistle and other nasties are enemies to your oaks. Don't till! This will only damage the oak roots and stimulate weed growth.
Mulch lots! Mulch helps hold in moisture, adds nutrients to the soil, aerates the soil, and gives a place for all those good garden organisms to live. You will only have to do this once, after that, your oaks should provide mulch for you.
Don't forget that shade is different on the coast from in the interior. Many coastal plants that like full sun or part shade would prefer full shade in the interior. Interior plants that like full shade are often happier on the coast in sun.
Many species that like full sun will grow in shade but may not flower much.