Wood chips mulch is an excellent organic choice for most garden and landscaping needs, but it is very important that only finished compost wood chips be used for gardening. This means that the mulch has been allowed to decompose for at least two years and will usually take on a gray color. As wood chips decompose, they use up large amounts of nitrogen, a nutrient needed by all plants to survive and thrive. In a garden, you do not want to make your plants compete with fresh wood chips for their primary nutrient.
How Wood Chips Decompose
While composting wood chips use nitrogen, they release soluble carbon, effectively feeding dangerous microorganisms that will ultimately get so hungry they will attack the plants you are trying to protect. Using mulch that has already been composted will drastically reduce the rate of carbon production and keep dangerous microorganisms to a minimum. Fresh wood chips are also more likely than composted ones to carry and spread disease, and are richer in minerals that can significantly alter the pH of the soil below, requiring you to recognize and make up for the difference.
If you have an excess of fresh wood chips you want to put to good use, consider using them to create pathways or for other general landscaping needs.