Perennials flower garden, how many inches topsoil is needed?

I found the dirt for my flower bed is full of rocks and was thinking of digging it out then having good topsoil delivered and filled in.





I have a bunch of different perennial seedlings almost ready to transplant. Any advice on how deep would be helpful, the flowers range from 1 ft to 4 ft tall.





Thank you in advance for your answers

Perennials flower garden, how many inches topsoil is needed?
why do the whole area?? dig out the spots you want to plant in and make a good deep hole of fairly good size and put your plants in that/gives you time to do the rest of the area and has a lot less expense; start your own compost bin and work from that for the rest of the bed. I have several flower beds that are soil that falls iunto the oh crap area but grow beautfor plants as where the plants meet the soil it is good compost.