I've come across two different words for "to dry" in my readings: 干す【ほす】 and 乾く【かわく】. I've seen both used to refer to things drying out (e.g. 「白妙の衣干すちょう」 from the 2nd poem in the 百人一首 or 「涙は乾いた」 in the case of the latter). I've also seen the related 渇く【かわく】, but that seems to be limited to topics related to thirst (e.g. 渇いた喉).
Can anyone provide some insight into when each is appropriate?