Caring for Oaks

In nature, oak trees can live 350 to 500 years, well over the human lifespan. They grow through several stages – seedling, juvenile (2-5 years), adolescence (15 – 50 years), maturity (50 – 200 years), and senescence (200 plus years) – as they form their particular shape and character. Oak trees require space and have particular soil, watering, and nutrition requirements. Caring for oaks in the garden requires basic understanding of these needs, and a vision that extends beyond the gardener’s own lifespan:

A Quercus agrifolia seedling. This acorn was most likely
"planted" by a squirrel in preparation for winter.

• Seedlings require lots of water to become established. This may mean deep, weekly watering (15 gallons) for the first two years.
• Once established, oaks require much less watering. Many California native oak species are adapted to the summer-dry climate. After three years, they should not be watered in summer, except during extreme or prolonged drought.
• Oaks establish a deep tap root, as well as many shallow feeder roots at the surface within the drip line. These feeder roots should not receive any direct water, to avoid root rot. This means clearing away lawn or plants under the oak.
• If you do plant under an oak, select species with compatible water needs, preferably within its natural plant community.
• Protect oak roots during construction projects. Problems may manifest in an oak tree long after the project is completed if roots are damaged during construction.
• Mulch with the oak’s own organic matter (fallen leaves, acorns, and catkins), up to, but not touching, the trunk. Do not use other fertilizers.
• Prune toward the end of summer, when the weather is still dry, since oaks seem to be susceptible to water borne pathogens. Work with an arborist to develop a strong limb structure through pruning, while the tree is young.

Urban oaks face continual menace from damage, overwatering, space constraints, improper pruning, and disease. With some care, they can live into maturity, giving pleasure to people, and providing habitat for birds, insects, and wild life.