CARE OF ESTABLISHED OAKS ON HOME GROUNDS

Oaks on home grounds require certain conditions to survive and prosper. Activities of concern to the homeowner are planting near oaks, irrigation and feeding, pruning, installation of home improvements, and disease and insect infestations.

Most native oaks in California evolved and prospered in an environment typified by a cool, moist winter and a hot, dry summer. Under natural conditions, surface soils are wet during the cooler months and become dry by summer. Natural vegetation growing beneath oaks flourishes during the winter and spring and dies by early summer, creating the well-known golden-brown landscape of California’s valleys and foothills.

Native oaks, however, remain green because their thick, leathery leaves and other adaptive features reduce their water use. The homeowner should attempt to approximate the natural environment in which these magnificent trees are originally found.

Planting Near Oaks

Only drought-tolerant plants that require no summer water should be planted around old established oaks, and they should be planted no closer than six feet from the base of the tree. Do not plant exotic grasses, ivy, azaleas, rhododendrons, or any other vegetation that needs summer irrigation.

Such plants develop thick mats of roots and thus inhibit the exchange of air and water the

established oak has grown used to.

There are a number of plants, some of which are native to California that can be grown beneath oaks. For an extensive listing of compatible plants useful for landscaping around oaks, contact the California Oak Foundation.

In place of plants, other types of ground cover can be used to landscape beneath oaks. When

installed properly, cobbles, gravel, and wood chips are good examples of ground covers that do not interfere with the roots’ ability to obtain oxygen and appropriate moisture.

Irrigating and Fertilizing

Native oaks usually do not require irrigation as they are well adapted to dry summer conditions.

Healthy oaks are even able to survive the excessively dry summers sometimes brought on by California’s variable climate. But if an oak has been compromised, as when impervious surfaces have been placed in the RPZ (root protection zone), occasional water may be helpful if done properly.

Mature oaks usually need little or no supplemental fertilization. Light fertilization may be appropriate in landscaped situations to replace nutrients supplied by leaves and other litter that normally accumulates under an oak in its native environment. If leaves are allowed to remain under trees, they eventually break down and supply nutrients.

Pruning

Excessive pruning or thinning of limbs may expose interior branches to sun damage, may stimulate the tree to produce succulent new growth that is subject to mildew, and, in some cases, may cause a decline in vigor or may kill a tree. Only dead, weakened, diseased, or dangerous branches should be removed.

Necessary pruning should be done during the winter dormant period for deciduous species and during July and August for evergreen species. Recent research has shown that tree paint, wound dressings, and sealing compounds do more harm than good.

Pruning should be performed by a certified arborist according to the pruning standards of the Western Chapter of the International Society of Arboriculture.

Excerpt from “Care of California’s Native Oaks”, Bulletin of the California Oak Foundation. Published by: California Oak Foundation, 1212 Broadway, Suite 842, Oakland , CA  94612,

For more information: visit: www.californiaoaks.org – or call: Phone: 510/763-0282.