Plants native to eastern Washington do best planted in the fall.  In our area, and all of eastern Washington, most of the precipitation comes in the winter so local species are adapted to do as much as they can even when the weather is cool. When you plant natives in the fall, put water in the hole before you put the plant in, let that water drain into the soil, and put more water in the hole as you back fill to wet the soil going back into the hole.  Doing these steps gives the plant roots moisture to start slowly moving it’s roots out over the winter and early spring and any rain or snow we get gives it an extra boost.  If it’s a normal winter and not a really dry one, you may not have to water your new plant at all next year.