Rake the old mulch off before top dressing -- you can reuse it along with some new mulch. I've top dressed perennial beds with 2-3" of compost without any problem, but adding 4-6" of topsoil without lifting and resetting the plants is, IMO, too much. Especially with your shrubs. You aren't supposed to bury the root flare on shrubs anymore than you are on trees. I suppose you could keep the new dirt pulled back from the root flare, but be sure to do that. This is also funny time of year for this project. Top dressings is typically done in the late winter/early spring when most plants are still dormant. And, again, top dressing usually involves purely organic matter, not topsoil. Cancel the order or put the pile out back and do the work in the early fall -- when it is also a better time of year to be lifting and moving perennials than right now when everything has already put on significant growth and we're moving into the hot and often dry summer.

Well, sometimes you can only do the task at the wrong time; you just have to know what the risks are so you can mitigate them. If you decide to do it now, which I agree is less than ideal, and to lift the plants, which I agree would be ideal, then it is like planting a new bed, and the plants will not be established for summer so you will have to water a lot to get them through.

If you don't lift the plants, you will lose some of them if not all; it depends on which ones they are. Some will not be bothered at all, but their growth may be altered. Let's take hydrangeas, which root quite well from the stem and so likely won't rot. So even if you kill off their original roots by piling on the soil, chances are at least some of the stems can form new roots and your bush, or what appears to be your bush but is really cuttings from it, will survive. But the story may be different for any grafted shrubs, say Japanese maples or a contorted filbert, and may be different still for shrubs prone to suckering.

In perennials, some will succeed in growing through the additional soil, others not. Or peonies, for example, will grow but not flower if they are planted too deep.

If you do keep the new dirt pulled back from the plants, you can make little rock wells around each plant you won't have the dirt rotting the stems, but it won't quite be the look of the full hilly beds you want.

Life is a series of compromises! Question is which ones you want to make here.

KarinL

Thank you! I wasn't planning on disrupting the shrubs or plants at all..I have 14 yr. old viburnums, black eyed susans and some popular green little shrub that I cant think of running across the front! I just have lost soil over the years due to rain and such..just wanted to loosen up the soil, add a few inches and remulch. The bed I wanted hilly is a tree and all black eyed susans. I don't want to bury them..I will give up the hilly look as a compromise and just add soil. thanks!