Chestnut Hill, schist under old canopy.

Chestnut Hill, zip 19118, is the northwest corner of Philadelphia, with Germantown Avenue running through it as the commercial spine and the Wissahickon Valley along its western edge. Much of the neighborhood is large stone houses on generous lots, built from Wissahickon schist, the gray, mica-flecked local stone. Garden walls, piers and steps are often the same stone. The tree canopy is old and heavy. To the north and east, Chestnut Hill meets Springfield Township in Montgomery County.

Stone walls built long ago move as roots grow and frost works the joints, and many were laid in softer lime mortar that should not be repointed with a hard modern mix that is stiffer than the stone around it. Walks and steps have settled out of level. Mature oaks and maples throw deep shade, compete with every bed and lawn for water, and leave a heavy leaf load in the fall. Established gardens have plantings that outgrew their space decades ago, and grading near old trees has to respect the root zone.

Walls, steps and walks get reset or rebuilt, with the existing stone reused wherever it is sound. Established beds get thinned, overgrown shrubs come out, the soil is reworked, and the replanting is chosen for the shade the bed has now. Thin lawns under the canopy are overseeded in September with a shade-tolerant cool-season grass. Then there is November, when a mature canopy comes down and the fall cleanup has to be sized to it.