Ancient Oak Trees

Saturday, September 20th, 2008 by Jenny Watts
    • Replace tired petunias with bright pansies, snapdragons, calendulas and stock for garden color this fall and winter.
    • It’s time to divide overgrown perennials that bloomed in the spring or early summer. It’s also a good time to choose and plant some new varieties.
    • Bearded iris are now available for fall planting. Their large flowers come in a dazzling array of colors.
    • When blackberry vines are done fruiting, prune back the canes which bore fruit this summer. Twine young canes around the fence or trellis.
    • Fall vegetable starts are still available for your late fall garden.

Living with Oak Trees

Native oak trees are a valuable asset to any piece of property. Their beauty is irreplaceable, and the shade and wildlife habitat that they afford are invaluable.

Oak woodlands and forests also sequester large quantities of atmospheric carbon, thereby contributing greatly to our health and well-being. In Mendocino County, we have large numbers of Oregon oaks, black oaks and canyon oaks. But the largest acreage by far is in tan oaks which sequester over 25 million metric tons of carbon in this county alone.

Oak trees can prosper in close proximity to our homes if care is taken to preserve the basic elements of the natural oak environment. But sometimes living under oak trees presents some conflicts.

Mature native oaks will not tolerate summer watering. They have been living for hundreds of years with the natural cycle of winter rains and summer drought. They are subject to root problems if moisture levels change significantly, since warm-moist conditions can favor harmful diseases. It is particularly critical that the trunks of oak trees remain dry.

However, if the winter season is unusually dry, then a supplemental irrigation in the early spring can complement natural rainfall. Water deeply, to one to two feet, in the outer two-thirds of the root zone.

Lawns or other ground covers are inappropriate under oaks, not only because of their water requirements, but also because their thick root mats inhibit the fine root development of the oak trees. Do not irrigate, plant or disturb the soil within 10 feet of the trunk. Organic mulches, however, are very beneficial in this area.

Beyond 10 feet from the trunk, drought tolerant shrubs can be planted. There are many attractive native plants that are well suited to this environment which will provide beautiful, low-maintenance landscaping. Rhododendrons and camellias require too much water to be compatible with oaks. Flowering currants, Daphne, Carpenteria, Nandina, and Oregon grape can be grown in this zone.

Disturbing the soil around old established oak trees can be a real threat to them. Changes in grade caused by mounding up soil or excavating it will destroy surface roots, and often result in the death of mature trees.

Minimize grading, digging, trenching, covering the ground with asphalt or concrete, landscape planting, excessive foot traffic, or vehicle parking well beyond the drip line of the tree. The area extending 6 feet from the trunk is the most vulnerable and should always be left undisturbed and uncovered.

Changes in drainage around an oak can keep the root area moist in the summer when it should be dry. Soil compaction can suffocate the roots and so can paving. Trenching in the root zone can kill a major portion of a tree’s roots and cause death of the tree. Disturbances beyond the dripline of the tree are usually tolerable to oak tree.

Take care of your oaks and they will give you shade, beauty and clean air for many long years.