Why fall is the appointment that matters
Most of our rain falls between roughly November and March. Everything that dropped out of the trees through September and October is sitting in the gutters when the first serious storm arrives.
That's the failure point. A gutter that looked fine in September overflows in December, sending water down the siding and into the foundation area at exactly the time of year when the ground is already saturated. Cleaning gutters in January means you're cleaning up after the problem instead of preventing it.
If you only do it once a year, do it in the fall.
The spring appointment
Spring cleaning clears what accumulated over winter — plus the seed pods, blossoms and early leaf drop that a lot of Peninsula trees produce heavily. It also lets you catch anything the winter storms damaged while there's dry weather to fix it.
When you need a third
Homes under mature oaks, redwoods, pines or eucalyptus generate enough debris to need a mid-season check. Pine needles are particularly troublesome because they mat together and pack downspouts in a way leaves don't.
If your property is heavily wooded, a check in mid-winter between storms is cheap insurance compared to fascia repair.
What clogged gutters actually cost you
Overflow runs down siding, which stains stucco and rots wood trim. Water pooling at the foundation is the expensive version. Packed wet debris is also heavy — heavy enough to pull fasteners loose and pull the gutter line away from the fascia.
There's a secondary problem people miss: standing water in a blocked gutter is mosquito habitat, and it sits right against your roof edge, keeping the fascia and roof edge permanently damp.
What about gutter guards
They reduce how often you need cleaning, not whether. Fine debris still gets through and accumulates underneath, and guards themselves collect material on top that needs clearing. Guards are useful; they aren't a permanent solution.