Mulching has the following benefits; suppresses weed growth, slows moisture evaporation, moderate soil temperature, and as a mulch breaks down it will improve the soil’s texture.
For trees and shrubs the type of mulch is less important than for Vegetable Gardeners. Using the wrong mulch around your vegetable plants can cause the plants to grow poorly and be susceptible to diseases.
You want to pick a mulch that has a low Carbon-to-Nitrogen (C:N) ratio. The main reason to use a mulch with a low C:N ratio is to ensure all your available nitrogen does not get tied up trying to decompose the high C materials.
In nature the first place a high C:N molecule looks for N is within the product itself. In the example of a wood chip there is not enough N available for proper microbial growth so the microbes search for sufficient N in the surrounding soil. Imagine the effect of available Nitrogen for your vegetable plants if the entire soil surface is covered with several inches of wood mulch?
Even worse, imagine if your entire soil structure was very high in carbon products such as wood chips? This would virtually tie up all the nitrogen in your soil trying to digest all the wood chips leaving very little for your plants.
The #1 rule we give our customers is to NEVER USE WOOD CHIPS, BARK, PINE NEEDLES, or SAWDUST. On the other hand the best types of compost are those with a low C:N ratio such as straw, dried grass clippings that have not been treated or fertilized with chemicals, or home-made compost.
If your choice of mulch is going to be rotted manure compost make sure you only use manures from animals where you know what they are eating. If an animal has a diet of hay that happens to be high in salts, a common occurrence, than your compost will also be high in salts. A high salt medium will prevent or slow plant growth.
The best manure to compost is from cow, pig, sheep, rabbit, lama, alpaca, and goat. The worst manure to use is from horses as it is very high in weed seeds. Chicken and duck manure is good to use, but unless you have a professional soil testing kit to test the Nitrogen content I would shy away from any fowl manures.