Twice a year for most homes: late spring after seeds and blossoms have dropped, and late fall after the leaves are down. Properties under heavy tree cover — pines especially — usually need three or four times. The fall cleaning is the one that matters most in a cold climate, and the window is narrow: after leaf drop finishes but before the first hard freeze. Clogged gutters hold standing water, that water freezes, and that's how ice dams form and push meltwater back under your shingles and into the house. The other failure mode is quieter. Gutters that overflow dump water straight down at the foundation, which is a common cause of a wet basement.