The ideal time to visit Isan is during the cooler winter months between late October and February, when the rains stop, the temperatures are more agreeable, and the flora more abundant. But this major rice bowl of Thailand looks its best when the vast plains are filled with the calming sight of rice fields in full production, which happens August through December.
The region is not affected by the traditional high season, either in terms of costs or volume of visitors, but you should be prepared for crowds and steep accommodation price rises during major public festivals. Discounts are prevalent during the off-season, particularly the rainy season, June through October.