Often I have had people email me questions on the differences between mulch and compost. Although the components can be used for the same purpose, they are both really different animals.
Mulch is classified as organic materials that are placed on the ground or around plants after planting. Mulch is often used to help retain moisture, reduce weeds and as the material breaks down, it helps put nutrients back into the soil. You can use almost any organic material as a mulching medium. You can use freshly chipped wood, bark, pine needles, straw or even layers of sawdust as a mulching medium. Plastic is often used around plants to help deter weed growth and although it is not an organic material, it is still considered a ground mulch.
Although compost can be used as a surface mulch, it actually has a completely different purpose. Compost is actually aged or partially decomposed organic material that is primarily used to be mixed with the soil to add nutrients for proper plant growth. Compost adds organic matter to the soil, improves drainage in clay soils, improves water and fertilizer retention in sandy soils, provides nutrients, increases soil microbial activity, and encourages earthworms. It will also act as a great mulch/top dressing for your existing flowers and over time break down further and improve your soil. As it ages, some of the components in the compost will leach away from the plant area but no matter what, you will gain a substantial benefit from using it.
Compost should be well aged before adding it to your soil. This is particularly true if you have manure in your mix. If you do not allow it to age enough, the mixture can burn the roots of your plants and cause problems for your plants.
In order to produce a good quality compost mix, you will need four basic components. You will need carbon that comes from components such as leaves, straw and shredded paper. The next ingredient is nitrogen. You can get these components from grass clippings, kitchen food scraps and manure. The final two ingredients are water and oxygen. The best way to start is to mix about a 50/50 ratio of the carbon and greens. As you place the components in layers be sure to apply water as you go. All the components should be as wet as a sponge. You should construct your pile to be around 3 feet by 3 feet or around 1 cubic yard in size. You must frequently turn the pile as it ages so oxygen will get to all parts of the pile. In addition, you should also wet down the pile each time you turn it. The smaller you make the components in the pile, the faster that they will decompose.