landscaping under fir trees
We have 4 big (40 years plus) Doug firs lining the road in front of our newly-constructed house. We want to disturb them as little as possible. In planning our landscaping design, we were thinking about either low-growing ground cover around them, or placing large-sized river rock around them, only deep enough to cover the ground, leaving room for precip penetration. We like the rock idea because it keeps weeds to a minimum & keeps us out of the area. Do you think the trees would be ok in this situation? The site had a 60-year old house on it previously & the ground around the trees was left fairly undisturbed, with a lawn fairly close to their drip line. The roots appear deep- I don't notice any pushing up anywhere.
To keep the Douglas-fir healthy, the general advice is not to do anything to change the soil elevation (add or subtract), avoid compacting the soil, avoid changes in drainage, especially anything that impedes water infiltration, drainage, and aeration. That said, a low-growing groundcover that will tolerate the shade and litter from the trees is a good option. Rock or other added materials could be used if you don't violate the advice above. But then there is the weed management challenge among the rocks...porous weed mats under the rock work for a while, but then new soil and weed substrate builds on top. From my forester's perspective, vegetative groundcover works well.