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Landscaping Around Our Oaks

The defining plants of our foothills are the oaks, in their spreading majesty and importance as a major wildlife food source. Right now they´re getting my attention closer to home, dropping acorns on our metal roof, and I want to consider their treatment in the landscape.

An oak tree is indisputably the most valuable plant in your landscape, adding an estimated $2,500 per tree to the value of your property. However, many home owners cannot settle for an oak grown naturally, without the embellishment of more showy landscape plantings. Accompanying grade changes, underplanting and irrigation often jeopardize the health of a native oak.

Appropriate landscaping respects the need of the oak for an undisturbed area, at least 10 feet out from the trunk, which will not be irrigated. Native plants can be established from this protected area out to the dripline. With their cycle of seasonal dormancy, requiring little summer irrigation and fertilization, many native plants are compatible with oaks.

What is not compatible is a lawn or heavily irrigated garden within the dripline, or even up slope from the tree. Down slope, away from the root zone, plants with higher water requirements can be considered. The area up slope from the tree should be planted with native or drought tolerant shrubs and perennials.

Before I move into a discussion of appropriate plants, I should mention “hardscape.” Impermeable paving in the root zone is not good. The soil cannot breathe nor can water percolate down into the root zone. River rock, gravel, pavers interspersed with soil or sand are all suitable ground coverings. Parking and driving in the root zone compact the soil and should be avoided.

One of my favorite landscape treatments in the root zone of an oak is to attractively site some large decorative rocks, then plant close to the rocks. Any hike in the high country will reveal one of Mother Nature´s favorite planting schemes—the use of a “nurse” rock. A plant will tuck itself up against a boulder, taking advantage of the cool soil at its base and the shade it offers. This arrangement, surrounded by a cleared area or mulch, is a very thrifty planting, conservative in its water demands and compatible with the requirements of the oak.

In considering what to plant near your oak, determine where the sun strikes during the day. If the area gets morning sun, a different spectrum of plants will be successful than those receiving an afternoon blast of light and heat.

The plants favoring morning sun or lightly filtered shade (from a high-limbed or tall oak) include mahonia (Oregon grape), carpenteria, mimulus or perennial monkeyflowers, western azalea, philadelphus, and salal. Favored perennials are the heuchera or native coral bells, Douglas or Pacific coast hybrid iris and blue-eyed grass.

Native bunch grasses and bulbs are excellent for any area underneath an oak, because of their ability to naturalize and their summer dormancy. Purple needlegrass is a lovely choice. It´s very showy in the spring, then quiet and undemanding in hot summer weather. These grasses are beautiful interplanted with native brodiaea and other bulbs.

I´ve got to put in a plug here for my hands-down favorite plant for this situation, the Pacific coast hybrid iris. Although they are showier at the CNPS spring plant sale, the plants available in the fall tend to be larger, and settle in more successfully. Read the labels for indications of color. They thrive in the dry acidic soil characteristic of oak shade, are heart stoppingly stunning when blooming in the spring, neat and sedate through their summer quiet time, and totally deer proof.

For the hotter afternoon sunny side of the oak tree, I´ve had success with the arctostaphylos or manzanitas, coffeeberry, the native fragrant sage or Salvia clevelandii, dwarf sandhill sage, California fuchsia (epilobium or formerly Zauschneria), the buckwheats or eriogonum, and the blue foothill penstemon.

You will find a great selection of these plants, plus planting advice, at the California Native Plant Society´s fall plant sale on Saturday, October 14, from 9 a.m. to 2 p.m. in the WestAmerica Bank parking lot up Highway 108.

Master Gardener Book: And speaking of gardening advice, the Master Gardeners of Tuolumne County are publishing a book “Sharing the Knowledge, Gardening in the Mother Lode.” A “must- have” book for every gardener in the Sierra foothills, it´s written by local Master Gardeners and beautifully illustrated by local artist Kristie Wilde. Proceeds from this book support the Master Gardener demonstration garden focusing on “best practices” for gardening and landscaping in the foothills.

This book may be purchased at the pre-publication price of only $15.00 by contacting the Master Gardener office at 533-5696. See you at the native plant sale and see you in the garden.

Mary Anderson, a Calaveras County Master Gardener and owner of Lost Hills Nursery, has spent the last 25 years getting to know California native plants on her 10-acre property. She propagates many native plants from the seeds of her ‘mother plants.´ As one of the original members of the Sierra Foothills Chapter of the California Native Plant Society she shares her wonderful knowledge of native plants at the twice-yearly Native Plant Sale.