It depends on how thick the mulch is. Generally, you scrape away mulch and plant at soil level and the vinca will root through the surrounding mulch as long as it is not too thick....one or two inches or less.

You should also be aware that vinca can have an invasive habit in some areas of the country and so should avoid planting it adjacent to native or forested areas. It also does best in at least partial shade.......vinca in full sun will struggle and the foliage will bleach out.

Thanks for the info

Vinca will take over. It will grow in your mulch, over your mulch, in your lawn, in your garden beds. You will be cursing the fact that you ever planted it. As far as I can tell, you don't have to be careful about planting it at all if you want it to grow. If you don't want it to grow all over everything, then don't plant it.

I think it depends on the situation :-) I don't find vinca overly rampant or hard to manage at all. But it does function best as a single groundcover in a larger area (like surrounding trees or larger shrubs) as it can rather easily overwhelm smaller plants.