Finding plants that will thrive with oak trees can be a challenge. Mature oaks have wide, dense canopies, resulting in heavy shade. Oaks also require dry soil during the summer, and watering other plants beneath them may cause the trees to develop crown or root rot, says Master Gardener Barbara J. Euser. Some blooming plants, however, are highly compatible with oaks. They'll provide long seasons of color in the shade.
Hummingbird sage (Salvia spathacea) is a 1-to-3-foot perennial. From March to May, its spikes of vivid magenta tube-shaped blooms draw eager hummingbirds in search of nectar. Hummingbird sage, says Cal Poly San Luis Obispo, grows wild on the slopes of coastal California's live oak habitats. In some areas, it can form patches up to 100 feet cross. It tolerates full sun as well as shade.
Island Alum Root
Island alum root (Heuchera maxima) is a 3-foot tall perennial that grows wild on California's Channel Islands. Also known as coral bells, it has base clumps of deep green leaves. During the spring, the plants have showy spikes of delicate white to pale pink flowers attractive to hummingbirds. Island alum root is completely at home in dry shade, says the Southern California Metropolitan Water District.
Each of the many varieties of wild lilac (Ceanothus) is a perennial shrub. One of the low-growing ceanothus forms, Carmel Creeper (Ceanothus griseus horizontalis), is a popular ground cover for shady dry areas beneath oak trees. Like oaks, Carmel Creeper requires no summer water. Excessive moisture can give it root rot. In April and May, delicate spikes of sweetly fragrant blue spring flowers to its attractive, glossy green leaves. A variegated variety, Diamond Heights, has lime-green leaves with dark green center blotches that brighten the shade all year long.
Creeping mahonia (Mahonia repens) is another blooming ground cover suitable for planting beneath oak trees, says the Sonoma County Master Gardeners website. Standing from 1 to 3 feet high, this spreading evergreen has soft green leaves that may assume shades of peach or pink in the winter. From April until July, it has drooping clusters of fragrant yellow flowers. Bright purple berries follow them, making this shrub colorful through the year. Creeping mahonia, says the Lady Bird Johnson Wildflower Center, loves the shade and acidic soil found around oak trees, but isn't happy in windy spots or places with very hot summers.