Question
I'm interested in sprucing up my backyard.  I currently have areas on each side of the yard for flowers and plants.  Two different people have told me I need to raise my beds 4".  Can I order the topsoil and spread it around the existing flowers and plants(like you would mulch) in order to raise my beds?  Or, do I need to remove the existing flowers and plants, lay down the topsoil, and then replant?

Answer
Generally, yes.  

Depending on the plant types in your beds, the best time to do this "bed-raising" is in the fall.  If the plants are perennials or biannuals, so you don't miss out on their seasonal display, and because if you have evergreens/deciduous trees and shrubs, they are going dormant for the long winter.  

Raising grade is especially hard on established trees and shrubs.  Their feeder roots are usually only in the first 18-inches of soil, so adding material on top of their roots smothers their ability to exchange needed items like water, air (yes, they "breath" through the soil), and needed nutrients.  The number one reason trees don't survive is that people plant them too deep to begin with.  The number two reason is that they get buried with other stuff, later in life.

The good news is that transplanting is not that hard for most plants, with a couple of exceptions like Bougainvillea.  Here is how to go about it:  http://hgic.clemson.edu/factsheets/HGIC1055.htm

Also, good news for you back: you don't have to transport the plants too far.  If the plants are clumping like Iris, its a good time to divide them, anyway.  

If there are any dormant spring bulbs in the planters (like dafodils, or crocus), you'll probably lose them in the "bed-raising" process, unless you can find them all.  I usually "forget" they are there until next Spring Every year its, "Ah, thats where I planted them!!"

Hope it helps.  ~M