Having a majestic old oak in your garden can add beauty and interest to your home. So keeping it healthy and happy is important. Watering under the drip line (area of ground covered by the canopy of branches) can cause stress and increase the oak's susceptibility to diseases, especially if this watering occurs in the summer when the oak is accustomed to a dry period. Removing the leaf litter can lead to soil compaction, reduced moisture levels and increased abundance of antagonistic microorganisms. Tilling or changing the natural grade of the landscape can damage shallow roots as well as symbiotic microorganisms and encourage diseases. So keeping all these things in mind, planting a traditional landscape is nearly impossible. However, this doesn't mean that having an oak tree means having no landscape. In fact, there are hundreds of plants that will grow and thrive under oaks and they generally require very little care or irrigation. These are California native plants that grow under oaks in the wild. Here are just a few ideas.
Fuchsia-flowered gooseberry (Ribes speciosum) is a deciduous shrub that has deep-red fuchsia flowers that are hummingbird favorites. The glossy green foliage turns red in late summer prior to the plant going dormant for a small stretch before the rains return it to its former glory. This dormancy period has helped this plant survive thousands of hot dry summers in California with no rain. Thorns help protect the plant from being eaten by deer and rabbits. They also provide an excellent place for birds to take cover from predators. Fuchsia-flowered gooseberry is great for a shady bird garden.
Hummingbird sage (Salvia spathacea) is unique among California native sages, because of its preferred growing environment. Most California sages need full sun. However hummingbird sage is quite happy under oaks especially in the drier interior climates of California. It can be found thriving under ancient oaks in the wild with more than a foot of leaf litter. And second for its deep red color which is quite different from the blues, whites and purples of most other California sages. It spreads to make a nice ground cover. Hummingbird sage has large, fragrant mint-green leaves, and in spring, a multitude of giant burgundy flower stalks that attract hummingbirds. Along with its many other endearing characteristics, it is also deer-resistant.
See our article on deer-resistant landscaping
Snowberry (Symphorocarpus albus laevigatus) is a tough ground cover with a lacy habit and soft green foliage. It produces snow white berries in the fall that are left dangling on bare branches in the winter. Snowberry is deer resistant and, in most areas of California, needs no irrigation after it is established. Plant as a very low maintenance large scale goundcover. Because of its spreading nature, Snowberry is also great for slope stabilization.
These California native plants can be planted in winter to minimize irrigation under the oak and make use of rainfall. If the oak is still fairly healthy, the plants should establish within the first winter and be able to survive with little or no water the first summer. However, if the oak is unhealthy and starting to die, the plants may be harder to get established. An application of at least 4-6 inches of mulch, such as Scotts® Nature Scapes® can help immensely in this transition and will usually push things in the right direction. Never use plastic or newspaper as a weed barrier under oaks as this can cause anaerobic conditions in the soil, decreased absorption of water into the soil, and interfere with the decomposition of the mulch layer. Mulch should be placed on the soil surface and not incorporated into the soil. With a few native plants and some mulch you should be on your way to a stunning oak woodland garden.