what he said. just enough to keep them from drying out. they, the rhizomes, have no way of USING a lot of water until they've established roots and are producing green foliage. the first year is probably the most critical as to watering as they are beginning to establish a solid root system. once established, that extensive root system is very active and more capable than many folks think when it comes to finding water when need be. long slow, soaking waterings are more preferable than a quick 'drench' as the roots will follow the water so if they find it close to the surface, they'll probably prefer to stay in that area and we'd like them to develop a nice deep root so as not to have to water as much.