Spring (April to early June) is the finest time to visit Ashtarak. The Kasagh gorge sides come alive with wildflowers, and the apricot orchards that cover the surrounding hills are in full blossom in late April — the scent drifting through the town is remarkable. Temperatures are mild and the light is good for photography.
Summer (June to August) is warm and dry. The gorge and the monasteries are easy to visit, and the road to Mount Aragats is open. Midday heat can be intense, so start early and save the afternoon for shade. This is the busiest tourist season, and the churches see more day-trippers from Yerevan at weekends.
Autumn (September to October) is another excellent window — cooler, quieter, and with beautiful light. The apricot harvest is long over by then, but the landscape turns golden and the surrounding peaks often have an early dusting of snow on the higher ridges.
Winter is cold and can bring snow, but the churches are never closed. The gorge looks dramatic in frost or snow, and you will almost certainly have the place to yourself.