I'm a part time arborist in the past and gardener and have used wood chips a fair amount as I have had plenty of supply. I have cold winters, dry hot summers.
In my experience the timing of wood chip application is important. I believe it has to do with soil temperature. When applied in the summer (3-6 inches) at the height of the growing season, there is no real difference in growth rates, but soil moisture is very even and the garden does well. Applied in the fall results in insulating the soil, delaying the rise in soil temperature in spring and initial fertility problems. My tomatoes planted in this environment turned yellow requiring some supplemental fertilization (more than the truckloads of manure I brought in) early on especially when the spring turned cool. However, once the system warmed up, the garden literally took off. I ended up with huge beets and potatoes. It also protects the soil from compacting. Beautiful loose soil underneath. I believe it may also be useful in controlling foliar disease.
2 years after I applied this layer, the soil is beautiful, especially compared to new areas where I haven't added wood chips yet, retains moisture well. Will apply another thick layer soon.
