Hello from Licking County!  Thank you for letting me help you with your mulch question.  

The frequency on mulch replacement depends on a few things.  What type mulch you use, how fast it decomposed, and how deep you put it in.

Mulch should never be spread deeper than 2-4 inches.  You should never volcano your trees (see fact sheet).

I always opt for organic mulch at least double ground but preferably triple ground.  This type of mulch helps the soil and decomposes into it more quickly than the other types of mulch.  This in turn helps the quality of your soil.

If you have 2-4 inches of mulch left in your beds, do not mulch.  It is not good to have too much mulch on your beds.

Here are some fact sheets for you:

https://extension.psu.edu/mulch-a-survey-of-available-options

https://extension.psu.edu/mulching-landscape-trees

Let me know if you have anymore questions.  Hope this helps
Shelley

You’re welcome