Im using my amulet of nature for herb patches. However i wonder do i need to use it with herb patch EACH time i plant herbs,or only once in case it is binded to same herb patch forever unless i bind it to another patch?

The AoN binds to only one patch at a time. So you bind it once and just wear/rub it for updates.

It is binded to the same patch forever, you can easily test this yourself on the next farming run you do...

 

 

 

At first it will say "It is growing nicely"

 

 

 

Then it will say "It is ready to be havested"

 

 

 

Then havest and replant and it will say

 

 

 

"It is growing nicely"...