Sweetgum and oak litter
The inner suburbs traded shade for a maintenance calendar. A mature canopy — the oaks and sweetgums that make Kirkwood and Webster Groves look the way they do — drops something on the roof in almost every month: tassels and seed in spring, twigs through summer, leaves in November. Gravity collects all of it in the same two places: the valleys and the gutters.
Litter is a sponge
A valley works by moving water fast. A mat of leaves and sweetgum balls does the opposite: it slows the flow, spreads it sideways under the shingle edges, and then holds moisture against the covering for days after the sky has cleared. Shingles that stay damp lose their protective granules sooner, and a valley that spends every autumn under a wet mat ages years ahead of the open slopes beside it.
Sweetgum balls deserve their reputation. They are sized almost perfectly to lodge in a gutter without washing through, they do not break down over a season the way leaves do, and they interlock into a plug that holds firm. A plugged gutter in a thaw-and-refreeze winter backs meltwater up over its rear edge — against the fascia and the first courses of the roof, exactly where the covering was never meant to hold standing water.
Shade finishes the job
The same canopy that drops the litter also shades the slopes beneath it. A shaded north slope in this humidity dries slowly after every rain and holds its winter moisture longest, so the two problems compound: debris holds water, and shade keeps it from leaving. On a treed lot the two sides of one roof can age at visibly different speeds — worth remembering when one slope looks fine from the driveway.
None of this argues against the trees; it argues for a rhythm. Valleys and gutters cleared after the November drop, a look in spring once the seed has come down, and — on a replacement — valley construction chosen for debris: an open metal valley sheds litter that a woven shingle valley traps against its centreline.