Originally Posted by Malticulous
It's always best to pitch enough healthy yeast at or just below fermentation temp.
+1, and this applies to ales too. You don't pitch ales at 85°F, wait for fermentation, then drop them to 65.
At lager ferment temps, I get the impression that yeast are more active than spoilage organisms, so if you underpitch, you're better off waiting it out than raising the temp.