saw dust cuttings as mulch
Because of the firewood's age, the dust will not be as "hot" as new sawdust and should be fine to apply near plants on the soil surface as mulch.
Sawdust breaks down and starts to decompose quickly because of the small particle size and high surface area per particle. This sawdust is not composted, i.e. reached a stable point in decomposition, so it will be using up some nitrogen to decompose and you may want to supplement it--a little--with some nitrogen if you are working it into soil and planting soon. However, if you work it into the soil and wait a month, you should be good to go.