Gravel vac how often

My plants are slowly but surely spreading throughout the tank. My question is how often do u have to do a gravel vac with a planted tank I know it depends on the tank but is there some rule of thumb thanks.

 

I do it once a week with my water change. Just good practice to pick up any loose muck on the bottom of the floor with the vacuum.

 

Perfect as Zoom has it once a week.

 

Ok thanks