Can you plant flower seeds on top of mulch? Will they grow?
Mulch (assuming here that you're talking about organic mulch) does not have the kind of texture that is good for nurturing roots. It's too open and coarse in structure, and not chemically active, and does not retain moisture in the manner that soil does. Of course, there are some very strong plants that grow when their seeds are just sprinkled on top of the mulch -- usually we call them weed. But for most flowers, you need to scrape the mulch aside and plant in the soil. This article has general info and references for mulch: https://www.gardeningknowhow.com/garden-how-to/mulch/benefits-of-using-mulch.htm