How much mulch is too much? Are the shrubs and trees, such as they are, thriving? Even bark mulch will breakdown into valuable components of the soil eventually, but the larger the chunks, the longer it will take. Depending on the type of groundcover you choose, I'd be inclined to scrape away a few inches of the mulch and add garden or potting soil and then plant. The soil will provide enough of a base for the new groundcovers to take hold so they can then spread. Spreading may not be as rapid through areas of heavy mulch unless you select larger growing, more woody types like cotoneaster or kinnikinnick, whose spread is more determined by branch development rather than rooting at internodes.

I can't help you with your question, but being a person who needs something for mulch for a 1/4acre (insane slope), can't you offer the mulch to someone, free for them to haul away? try craigslist.org or freecycle.org - someone will be really happy.

If the wood chips are still decomposing, they are using nitrogen, so it would help to add some soil around the new plants and keep fertilizing lightly. You may have many rodents burrowing thru the mulch so roots may be eaten.

Thank you for all your replies. Very helpful. My instinct was that plants of course need dirt, but people kept telling me that mulch was great and to leave it (maybe they thought I was exaggerating about the amount). I'm going to buy some topsoil this spring, especially now that I've seen that the trenches where he dug out the soil and replaced it with mulch fill up with water during heavy rains, and the mulch floats into the grass. Thanks again!

More than 2-3 inches of mulch can be harmful. I would remove all but a 2 or 3 inch layer, and more if you need to be able to plant your groundcover in the soil without smothering it. Also, make sure that your shrubs and trees don't have mulch piled up against the stems or trunks. A ring of mulch around a plant should look more like a donut rather than a volcano.

Hi,
I just planted some new periwinkle/vinca ground cover in a spot nice little bed that gets morning sun. I also planted some alyssum along the edge of the bed. After the plants were in the soil (with fertilizer and new topsoil mixed in) I spread some colored woodchips that has Preen weed preventer in it. I'm worried though, that the periwinkle won't spread or will slow down the growth becuase of this type of mulch. And I'm also worried the allysum won't spread or reseed.
Has anyone ever used this type of mulch around alysum or periwinkle?

Thanks!