Neither one is right or wrong. Do whatever is most convenient to you. You can mulch the whole bed, and then push it aside to make your planting holes or mulch after planting.

I grow mostly perennials, so the mulch goes down around existing plants. But if I buy a plant after the mulch is down, well, then, I push it aside.

In a large new bed, it is much faster to prepare the bed and add mulch before planting. Then you just push mulch aside and plant the annual. But, in 50 years of gardening, I have never had a big empty bed to start with. So, mulch is usually the last thing in the process each spring.

I found it easier to plant first, then cover the plants with a pot, or container, and then you can just dump the mulch right on. Once you spread it around just remove the containers and there you go.

I like the idea of covering the planted plants with a pot. If I plant after I mulch, there's always dirt on top of the mulch, not that it makes much difference in the long run.

Now, if I could just find the time to do the planting and mulching. I am starting a new bed on the side of the house and so far all I've done is dig out old rhodos, lots of roots and ivy runners. I'm also finding old balls and toys that my kids threw in theri 20 years ago, along with remnants of a do-it-yourself roofing project.

I also prefer to mulch after planting. When I mulch before planting I find that the mulch gets too mixed up with the dirt from my plantings and I don't have that clean and clear cover look that I prefer.

I also live in an old house. Digging out each new plant bed, or just cleaning up exisiting beds, is always an adventure. I have dug up enough flagstone to create a walkway, several old medicine bottles, an old lysol bottle, chips of broken china, and two pieces of stone substantial enough that I moved them to a more prominent plant bed with a severe slope for "decorative" effect. I've also found other things that are just plain trash, old toys, cleaning sponges, brooms, and most recently deteriorating plastic cups from casinos in AC. Yuck, yuck, yuck!