Sorrel/Sourwood Trees: Are They Drought Tolerant?

Here in the Pacific Northwest,  some gaps have begun emerging in our bloom calendar in the late summer and early fall. This is due to drought making it harder for native wildflowers to bloom and fill with nectar. One tree we are using to provide pollinator forage for that time is Sourwood, which is native to the eastern US.

However,  the literature around this tree conflicts as to its drought tolerance. Does anyone know or have experience with this? We are irrigating for the first years but hope for the trees to reach self sufficiency around year three.