There is a limit to how much re-bloom you can get on nemerosa types from old stems. You can cut back the worn down old stems and let the new rosettes do their thing, whether it is further bloom or rebuilding food stores and other biomass for next year.

I noticed that with my 'Caradonna', it didn't bloom much the first year, even with consistent dead-heading. This 2nd year, it's like it woke up, doubling in size and putting out a lot of blooms. It's still blooming, and producing new blooming stems, and doesn't show signs of slowing down. I don't cut into the leafy area of this one at all, however, just trim the old bloom stems down to the nearest joint.

Brenda

I'm not sure if this will work with "Marcus", but....... When I dead head Salvias I try to only remove the stem-part with the blossoms, not the leafy part below. It seems there might be new flowers-in-the-making in those below-leaves.