Measurement - by cup or weight?

I am looking at the recipe for the kidney cleanse and it say "1/4 cup of Hyndrangea root" (and etc.) And then, the instruction says "soak" the roots...
I thought I have to buy the fresh root, which is sold by weight. but how can you measure 1/4 cup of it? Should I mince it into tiny pieces first before measuring it? And then the "1/4 cup Uva Ursi leaves"...Is there a recipe that gives ingredients by weight to make the preparation exact? (Probably, it doesn't have to be, but I don't know this.)
I went to one website that sells "powdered" root, but then you don't soak powder, or don't you?
Also, would buying the powder form be ok instead of buying the fresh roots (easy storage, and longer life?). I haven't bought anything like this over the internet and I'm not really sure if I would be getting fresh roots and not dried ones.
Any comments?
Please dispense if this had been asked before. Thanks.
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