Planting Under Oaks

June 30, 2016

While you design and construct your landscape under an oak tree, keep in mind that California is experiencing a massive decline in the health of our oak woodlands. Two contributing factors to this are status quo management procedures and a disease called Sudden Oak Death, caused by the Phytophthora fungus. Educational institutions across the state are currently conducting research on how to treat and prevent S.O.D. In the meanwhile, we landscapers can help to preserve the heritage of our oaks by being aware of the best known management practices.

Here are the three most common landscaping mistakes that can sicken or kill an oak tree – disturbing their extensive root systems, over-watering during the summer season, and choosing inappropriate companion plants. With that in mind, we’ve gathered some tips to help keep your oaks in good standing.

  • Envision the root systems. Oak trees form both a single, deep taproot as well as a system of many shallow roots that spread horizontally to the edge of the leaf canopy.
  • Do not plant or place anything within 10 feet of the trunk.
  • Use hand tools whenever possible. Refrain from using machinery that causes compaction to the soil, or that rips through roots while digging. Do not lay pavement under the tree. Do not dig large trenches.
  • Do not overwater. Established oak trees typically do not need supplemental irrigation. In years of extensive drought, irrigate once a month or less via a drip line that directs water to the outer edge of the canopy. Keep in mind that moisture around the roots in warm weather creates an ideal breeding ground for Phytophthora and other disease-causing fungi.
  • Mulch for water conservation, fertilizer, and to minimize weeds. The best mulch is composed of fallen oak leaf litter and an application of wood chips. This will decompose slowly and act as the only time-release fertilizer that oaks need, typically.
  • Do not over-prune. Only prune off dead branches or branches that touch the ground. To minimize the spread of disease, only prune in summer when disease-causing fungi are the least active, and do not remove pruned green waste from the property.
  • Plant in fall when the soil is warm and moist. This gives new plantings the most time to establish themselves before the next drought season.
  • Select appropriate companion plants. Go with California and Mediterranean natives since these will likely have drought adaptations similar to oaks. Find plants that will not compete for water or nutrients. Choose perennials over annuals. Use understory plants that can thrive in filtered sunlight. Consider the mature height of the plants. Research the aggressiveness of their root systems.

Refer to our Planting Under Oaks collection page to view a list of suggested plants that are known to do well under oaks. And look for the Oak leaf icon at the bottom of our plant profile pages to know if that is appropriate choice for under oaks. Contact our sales department to place an order today – 925-829-6006 or