A:     The coast live oaks that grow wild on the hills along the Central Coast also make beautiful landscape trees in our yards. Because common shade-loving bedding plants need summer water to survive, planting them beneath oaks can be detrimental to the tree’s health. Warm moist soil caused by summer watering encourages oak root fungus (Armillaria melea). It enters the roots of oaks and can kill the tree slowly over many years. To reduce the spread of oak root fungus, planting under oaks should be limited to species that do not require summer water.

Flowering shrubs that will add greenery and color under oaks are easy to find in local nurseries. The evergreen Ceanothus does well in the partial shade of oaks. There are many low-growing varieties such as C. griseus horizontalis and C. rigidus that can be planted with other colorful shrubs for a variety of texture and color. For a “fast fill” while Ceanothus expand, plant California iris (I. douglasiana) with their elegant purple, blue, white or cream flowers. or catmint (Nepeta faasenii) with its lavender-blue flowers. Coral bells (Heuchera spp.) with dark green to purplish red flowers cover ground under oaks and provide tiny colorful flowers above foliage. Red valerian (Centranthus ruber) is another drought-tolerant plant that thrives under the canopy of oaks.

Blue fescue (Festuca ovina “Glauca”) form small clumps of grass, and the larger fountain grass with graceful three to four foot pinkish plumes are interesting choices for oak underplantings.

Plant groundcover before winter and water lightly the first year to encourage root expansion. After that, let the oak and its underplantings “go native” enjoying our California climate.