Answer: Oak trees are beautiful to look at but are a challenge to plant under. Oaks don't like to have their roots disturbed and they don't like competition from other plants; oaks prefer dry conditions and many other plants won't grow under the dry and shady conditions of oaks. But there are a few plants you can plant, providing you keep them 6-10' away from the trunk of your oak:
Autumn sage (Salvia greggii) Bushy 3- to 4-foot shrub bears red, salmon, or purple flowers from late spring to summer.
California iris (I. douglasiana). Knee-high plant with purple, blue, white, or cream flowers in spring. Related Pacific Coast hybrids also work well; they need a smattering of summer water.
Catmint (Nepeta faassenii). Lavender-blue flowers make 2-foot mounds in late spring, early summer.
Ceanothus (California lilac). These native shrubs are most effective around oaks. Low-growing types such as C. griseus horizontalis and C. rigidus 'Snowball' reach 2 to 6 feet tall. Clusters of lavender-blue or white flowers appear in spring.
Coral bells (Heuchera). Compact perennials with roundish leaves in shades of dark green to purplish red; dusters of coral pink, red, or white flowers in spring or summer.
Daffodil (Narcissus). Flowers from February through April, then dies back and doesn't need water in summer.
Red valerian (Centranthus ruber). Perennial 3 feet tall that blooms from spring into summer.
Rosemary (Rosmarinus officinalis). Upright (to 6 feet tall) or prostrate (to 2 feet tall), plants have aromatic dark green leaves, plus lavender-blue flowers in late winter or early spring.
Santa Barbara daisy (Erigeron karvinskianus). This 20-inch perennial is covered with pink or white daisies spring into fall. Blooms best with extra light.
Hope these suggestions are helpful!
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