Try scaling the mulch geometry down, in the Geometry section OR if you're feeling adventurous, recreate smaller clumps of mulch, using the original geometry of the presets.
In my opinion however, this specific usage of mulch, in a small plant pot, using Forest Pack, is kind of over kill. Maybe a decent soil texture and a displacement map, would be better suited to that task. I rarely use the mulch presets and if I have a small area of what is required to have planting and need s to look like soil/compost, I prefer to use a simple texture or maybe a bland of two or three and displace the surface with a noise texture or displacement map. RD-Texture.com produce some incredibly useful soil and ground textures but with a bit of patience, you can produce perfectly usable soil textures, for no cost at all.
Hey you could even render a large area of mulch, from directly above and save that as a map and if you know your way around the render engines render elements, maybe even a very usable displacement map too.
By the way, I am not saying don't use Forest Pack, the latest v7 is insane, I'm loving the new functinality and the hedges presets are definitely one of the most useful additions in my workflow. The number of gardens I have had to create, plus surrounding, landscapes, fields, woodland etc., has certainly given this amazing plugin a work out. I just think the use of the mulch preset, for adding soil to a small plant pot, is maybe not the best solution.