The obvious time to visit is May, when the roses are in bloom and the festival takes place. The valley is genuinely spectacular in mid-May when the flowering peaks, and the festival itself, usually over a long weekend, adds to the atmosphere.
For trekking in the M'Goun massif, June through September is best — the high passes are snow-free and the alpine meadows are green. Avoid July and August in the valley itself, where temperatures can exceed 40°C. March and April see some lingering snow at altitude but are pleasant in the valley.
Winter (December to February) is cold at this elevation (around 1,450 m) and snow can close the higher passes. The town remains open and guesthouses operate year-round, but trekking options are limited.