Last fall I put down 2-3 inches of cedar mulch over my shrub and flower bed. My wife hates the color and now wants me to use a darker hardwood for mulch. Is it okay to mix the cedar mulch into the soil and then add a layer of hardwood mulch on top? Will the plants still get enough oxygen and water to prosper?

No, that's not a good idea. The problem with mixing un-decomposed woody material with the soil is that the fungi that decompose it need a lot of nitrogen. If it cannot get the nitrogen from the air, it will take it from every nitrogen source it can find in the soil. It gives the effect of chlorosis, or yellow plants. That lasts as long as it takes to decompose the woody stuff.

I don't know anything about nitrogen or fungus, but I can speak from experience that tilling raw mulch into the soil will lead to yellowing of plants.

Why not just layer the hardwood on top of the cedar? It will do well where it already is. And I've seen it recommended to apply hardwood mulch as much as 4" deep in ornamental beds.

David,

I am getting ready to make some azalea, camellia, and gardenia beds and the Dirt Doctor says to mix 50% compost and 50% cedar mulch to make the bed for them. Won't this cause the chlorosis you said would occur when mixing cedar mulch w/ soil and damage my azaleas, camellia, and gardenias.

you don't make the bed with it, you use that mixture as the mulch, top layer, not tilled into the bed material.

In the Dirt Doctor's book Texas Gardener and in the bed prep for Azalea's in the library it says to mix 50% cedar mulch and 50% compost to make the bed for azaleas as well as camelias and gardenias.

The concern is, as I understand it, that Howard's book says to mix the mulch with the compost and plant in it, not under it. I'm going to ask some folks about that.

Howard's books says to mix compost w/ mulch only for azalea, camillias, and gardenia's.

There's some good and bad information here. Large textured cedar mulch mixed int the soil will cause some nitrogen problems. On the other hand, fine textured cedar mixed with compost and other organic amendments will not and the entire bed needs to be made of the mix. Coconut fiber is also a good ingrient. No soil should be used in the azalea beds. Well - a very small amount can be used to innoculate the beds with the native soil microbes.