Our favorite companion trees for rhododendrons are oaks and pines. They have deep, non-invasive roots, produce a non-matting mulch that lets in oxygen, and they give open shade. As a general rule, trees that are native to drier areas have deeper, less invasive roots. For that reason, most of the trees native to west of the Cascades have surface roots--they don't have to go deep for water (firs, cedars, spruces, maples, etc.) Madrona and shore pine are two exceptions, but they grow naturally in unique environments. We still encourage the use of native trees--just give them appropriate space.

Of course, the other general rule is that the larger the tree, the more demands it will place on its immediate environment. Large maples are invasive, but we love vine maples and Japanese maples, dogwoods, and numerous other small trees.