Unfortunately, most wood chip material is sold as a fresh material rather than as a composted or aged material. The chips decompose slowly, but as they decompose, microorganisms use nutrients from the soil that might otherwise be available for plant growth. Non-shredded leaves and grass clippings can form a thick mat that makes water penetration nearly impossible. If sawdust is used it should be well aged, otherwise it will be difficult for water to move into the soil. Uncomposted sawdust is low in nitrogen and will rob nitrogen from the soil as it decomposes.
Anaerobic decomposition is often a problem with leaves or large piles of wood chips.
The mulch will have a smell of vinegar, ammonia, or sulfur. Damage usually occurs within 24 hours after application. The material should be applied on bare soil before or immediately after planting. Fasten the material to the soil to prevent weeds from pushing them up. Avoid getting soil on top of the material.