In the PNW, just South of Tacoma, I'm planting a Wintergreen Barberry hedge
about 8ft away from large mature fir trees. The soil is fairly fertile with
lots of worms, but I'm concerned that the trees may not be leaving enough
nutrients for the new hedge.

Should I just plant, mulch and be done with it, or should I add anything to
the soil to offset the trees? If I add, would that just make it worse
because the trees would start encroaching on the hedge's space for the sweet
nutrients I added?

Thanks,
Bob