This resource will be updated to include new information as we find it.
Mulch is organic material on its way to become compost. Compost is fully decomposed mulch which has turned into really healthy soil. Compost is mixed with existing soil or spread on top to provide extra nutrients for plants, and mulch is laid on top of soil to create a barrier that helps keep soil moist. Over time, mulch used this way will itself degrade into soil.
The only advantage to adding a wood mulch over compost is to further suppress weed development. Compost tends to be a rather fertile seed bed and while a good layer of compost will suppress any underlying weed seeds, it simply provides a a very hospitable habitat for germinating windblown seeds. The good news is they are usually extremely easy to weed out as compost is generally quite loose and fluffy.
Otherwise . . . compost is just as efficient a mulch as bark or wood chips in moderating soil temperatures and conserving moisture and far more efficient in releasing nutrients. With any mulch, you need to apply 2-3 inches — any less will not have the same effectiveness and more is just a waste.
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Any material you place on your soil to 1) aid in “weed” suppression, 2) aid in moisture retention, 3) aid in controlling soil temperature, and 4) aid in adding organic matter to your soil is mulch. I have no idea why some people distinguish between mulch, compost, and other stuff, or why people get so confused over what is a soil amendment and a mulch (the same material can be both).
Compost can be used as mulch and the sun beats down on the compost and dries it out which slows the bacteria that are digesting it, . . . covering that compost with another mulch material, ie. wood chips, will help keep the compost more moist and the bacteria more active.
Does compost spread over the garden need to be covered with another material? It is your choice. Do you want to keep that compost moist and the bacteria more active or are you okay with letting the sun dry that compost out?
Gardens Alive has good information as well.
Composting How To
Basically, there are two methods for composting:
HOT – where you turn ingredients, introducing air and creating heat which cooks the compost and turns it into soil in several weeks; and
COLD – where you add to a compost pile but don’t turn its contents. You just let it sit and allow time to do its work. In about 2 years you’ll have good, composted soil.
The University of Minnesota provides a detailed tutorial on which items, and how much of each, you can put into your compost and illustrates how to use three types of compost containers. The report discusses using a trash can for composting and here’s a discussion about some of this container’s pluses and negatives. More on bins here.
Take Florida’s Online Composting Center free tutorial “Compost Happens!” for a comprehensive, step by step lesson on the hows and whys of composting.
Mulching FAQ from Garden Web.