Do oaks need much sunlight? Yes—and no.

Chestnut oak saplings (Quercus prinus) bide their time in the understory until a tuliptree in the canopy falls, admitting more sunshine so they can mature.
Photographer: Sam Sheline, courtesy of NatureServeMany oaks in the eastern United States can successfully germinate from acorns in partial shade or even fairly heavy shade. But their growth will be slow, and they will not reach maturity without eventually getting plenty of direct sunlight.

Imagine an acorn on a shady forest floor. It takes root and becomes an oak seedling, then a taller, slender sapling. It may persist in the understory for many decades, receiving only filtered sunlight.

In time, perhaps during a summer storm, a large limb of a tall tree nearby breaks off, or a whole tree falls, and sunlight penetrates the forest canopy. The sunlight triggers growth in the small oak. When such a forest-grown oak is several decades old, it can begin to produce acorns if it continues receiving direct sunlight.