So with walnut sawdust you have two very separate problem.
1st is that it is sawdust, which means that it has a huge surface area so the soil microbes are going to quickly consume it and in consuming it quickly they are also going to quickly deplete the other available resources in the area that your other plants needs. To support all that cell division the microbes/fungi are going to use up all the calcium/mineral/nitrogen/amino acids/water and you plants are going to suffer. So use logs or at least woodchip that breaks down slower.
2nd is that walnut has juglone that suppresses
alot of plants, luckily pecans, walnut, heartnut, shakbark-hickory, butternut, etc are all in the same juglans family.
https://en.wikipedia.org/wiki/Juglandaceae
With them both being in the same family it will not affect the plant. The fig/mulberry family is also immune to said compound.
Iterations are fine, we don't have to be perfect
My 2nd Location:Florida HardinessZone:10 AHS:10 GDD:8500 Rainfall:2in/mth winter, 8in/mth summer, Soil:Sand pH8 Flat