The Dordogne has warm, sunny summers and mild springs and autumns. La Roque-Gageac's microclimate — created by the south-facing cliff trapping heat — means the village is noticeably warmer than the surrounding countryside, and the exotic plants in the clifftop garden thrive because of it.
July and August are the busiest months by far. The single road through the village becomes genuinely congested, gabare queues stretch back from the landing stage, and parking is difficult. The village is still magical, but you share the magic with a great many people. May, June, and September are considerably calmer and the light is excellent — the golden limestone glows particularly well in the lower sun of early morning and late afternoon. October brings autumn colour to the walnut groves along the river and is arguably the most beautiful month of all, though some boat services may have reduced hours.
December to February is quiet to the point of dormancy: most restaurants and tourist facilities close. A midwinter visit gives an extraordinary sense of the village returned to itself, the cliffs dramatic in rain or frost, but you'll need to plan carefully to eat or find accommodation.