Oregon white oak, or Garry oak (Quercus garryana), is a difficult tree to garden under because it can't stand the summer irrigation that many other plants require. Too much summer water makes the Northwest native vulnerable to disease and early death.
C. Ivan Vistica, who lives near Woodburn, Oregon, found the perfect solution: He underplants his white oaks with drifts of daffodils. They bloom two months before the deciduous oaks leaf out and start casting shade. Neither the oaks nor the daffodils need any extra summer water. In fact, daffodils have the best chance of naturalizing if you allow the foliage to wither and let the bulbs dry off in summer.
Vistica started this planting about 1990 with double-flowered daffodils that had naturalized around his farm. He transplanted them under the oaks, spacing the bulbs about 7 inches apart in rows 9 inches apart. He mulched them with oak leaves and has never fertilized.
Planting time for daffodils is in fall, but now is the time to look at flowering daffodils to see what kinds you like.