The best time to visit Kakheti is late September and October, when the harvest (rtveli) is underway. Every family winery is pressing grapes, the smell of fermenting wine hangs over the valley, and the landscape is at its most colourful. The major monasteries are busy with pilgrims around Alaverdoba in October — worth timing a visit around if you can handle the crowds, or worth avoiding if you cannot.
Spring (April and May) is also good: the valley is green, the Caucasus still snow-capped, and the roads quieter than in summer. July and August bring heat to the valley floor — manageable, but not ideal for walking. The monastery roads are paved and accessible year-round, though the David Gareja track south of Tbilisi can be rough after rain.
Winter visits are possible. Telavi is quiet, some guesthouses close, but the ones that stay open often offer good prices and genuine hospitality. Snow on the Caucasus adds to the views.