I apply compost on top of the soil, rather than tilling it in. But I usually mulch on top of that with some other organic mulch- leaves, grass clippings, or wood. I do that to keep the compost moist so organisms stay active, and also for weed suppression. Weed seeds can easily sprout in compost.

Karen

As said above, compost and mulch aren't the same thing and can't be used interchangeably. So if your primary goal is mulching for weed blocking and appearance then compost isn't what you want. Its appearance as a mulch lacks eye appeal for many and it does little to keep down weeds.

But if your primary goal is soil improvement and supplying nutrients to the plants, then compost is great.

Thus the combination of the two is ideal. Lay down a layer of compost and then cover it with an attractive mulch. That ways you get the best of both. ;)

But please take note of the quality of your city compost BEFORE using it. City composts can be good but they can also be very bad with all sorts of unknowns and contaminants included in them. Search 'city county compost' here for several previous discussions on the problems associated with them.

Dave

I disagree totally with Dave :-) Mulch and compost can be used interchangeably - mulch is simply a soil topdressing and can be comprised of any number of materials including both organic and inorganic products. There is absolutely NO reason why compost can't be used extremely successfuly as a mulch......it's the only type of mulch I've used in my garden (and many clients' gardens) for years. If applied in an appropriate thickness, it has the same weed supressing capacity as any other mulch, it insulates the soil to the same degree and retards evaporation of soil moisture and IMO, looks as good, if not better, than other commonly used mulches like bark nuggets, pine straw or wood chips. And it has a greater ability to provide nutrients and improve soil structure than most other mulches.

With regard to weed supression - a 2-3" thickness of any type of mulch will prevent most existing seeds from germinating. Seeds that blow in or travel from existing plants elsewhere can germinate easily in fine textured compost, but that is also the situation with most other fine textured organic mulches, like ground or shredded bark. The coarser the texture or larger the size of mulch particles, the less readily blown-in seeds will germinate.

I will agree that the quality of any commercial compost can vary widely. Fortunately, I live in an area that pioneered municiple composting from yard waste and that compost is tested regularly for a variety of possible contaminates, is certified organic, has a good chunky texture and rich, dark, earthy color and aroma and is distributed and sold throughout my area. Many professional horticulturists and landscapers swear by it. YMMV.

Compost can be used any way mulch can. Mulch cannot be used any way compost can. You wouldn't want to work mulch into the soil like you could with compost.

tj

Compost can be used as a mulch, but as gardengal points out to be effective your mulch needs to be at least 3 inches thick, more is even better. When used as a mulch compost will tend to dry out and since the bacteria that work on compost need a moist environment to function in they stop functioning, until there is enough moisture to go back to work. I've not ever had enough compost to be able to use that much for mulch, but I do put down a 1/2 inch layer of compost on the soil and cover that with 4 to 6 inches of of another material (usually shredded leaves) to help retain soil moisture, keep the soil temperature more even, add organic matter to the soil, and suppress "weed" growth.

"Compost is going to act as a mulch anyway, right?"

Right!! It will also feed the soil and encourage a good worm population. I have been mulching with compost for a few years now and I can only say good things about this practice. I do it early since by mid-June the plants are bursting from such a good thing. Here's one example.

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Compost is just mulch at the end of the decompostion process. A new bed with lots of bare soil needs a hefty layer of rich (compost). Rich, dark, double shreded mulch looks good and you only need a light top dressing.

Much of my property is wooded and full of back breaking stone. Rather than continue to deal with digging out, I decided to build up with free landfill mulch. Over 20 years of this has given me (up to 24" deep) black, rock free soil. These areas are very easily weeded. I continue to top dress with free mulch in the these beds but use pine bark nuggets and dark, double shreded hardwood in the more open "asthetic" areas (the money areas).

Wood chips are slow to decompose and ideal in paths and under playground equipment. They aren't pretty and often cost as much as double shreded. Once the landscape grows in densely enough, pure compost would be fine.

"Compost is just mulch at the end of the decompostion process."

Since mulch can be organic or inorganic (sp?), I don't think most people would care to wait for shredded tire as mulch to break down.

Even if the mulch were an organic mulch such as bark pieces, I would not think it would be as high in nitrogen as compost.

Non organic materials do not decompose-didn't even consider ground up tires or stone. The stuff is too hard to remove when a change of landscape is desired and it makes for WAY too much work to dig up and remove.

Point being, wood chips take a long time and added nitrogen helps to avoid soil depletion.