What to plant under oaks and pines?
Although we field all sorts of garden questions at Sunset, the query we get most frequently from readers is what they can plant under native oaks and pines. Both trees create tough environments that demand plants capable of tolerating dry shade, slightly acidic soil, and falling leaf litter. Native oaks must have dry soil in summer or they risk developing oak root fungus. And the water-hogging roots of pines create dry conditions.
In Sunset's gardens, we've been planting under oaks and pines for about 40 years, so we've come to know which plants work. To round out our suggestions (see "Good Companions," page 79), we consulted with gardeners, landscape designers, and the California Oak Foundation, a nonprofit group dedicated to protecting and perpetuating California's native oaks.
Under oaks, plant companions that like it dry
Western native oaks love the Mediterranean climate along the coast, with its wet winters and dry summers. Most shade-loving bedding plants, however, need summer water to survive, and if you give it to them, you'll also supply the warm, moist soil that's congenial to oak root fungus (Armillaria mellea). This fungus enters the oak's roots and usually kills the tree slowly over many years. Even after you remove the tree, the disease remains in the soil, attacking other susceptible plants, including elms, grapes, pines, and rhododendrons.
The most at-risk species include coast live oak (Quercus agrifolia), canyon oak (Q. chrysolepis), mesa oak (Q. engelmannii), Oregon white oak (Q. garryana), California black oak (Q. kelloggii), valley oak (Q. 1obata), and interior live oak (Q. wislizenii).
To reduce the spread of oak root fungus, underplant the tree with droughttolerant flowering plants and ground covers. Experts recommend that you keep all plantings 4 to 6 feet away from the oak's trunk. You'll need to give the plants a little extra water their first summer, but after that, they should do well on what nature supplies. When you do irrigate, don't water within 4 feet of the oak's trunk or allow standing water to collect there.
In addition to the plants we describe, you'll find a wide selection of oakfriendly shrubs, ground covers, perennials, grasses, ferns, bulbs, and annuals identified in the booklet Compatible Plants Under and Around Oaks (California Oak Foundation, Oakland, CA, 1991; $14.25; 510/763-0282).
Beneath pines, choose plants that "swallow" needles
Pines drive many gardeners to despair. Their roots suck the moisture out of the soil, making life under them difficult for many plants. Their falling needles (pines drop about a fifth of them each year) can smother lawns. Some gardeners just give up and let the needles accumulate, but that can create a fire hazard.
There are alternatives. It's hard to go wrong if you plant a skirt of shrubs just inside a tree's drip line; you'll never see the needles that fall behind them. If you choose open shrubs with large leaves, like rhododendrons, most of the needles will drop through their branches and disappear Avoid planting shrubs with dense, small leaves, which tend to trap the needles.