Can I cut the roots of a redwood at the dripline 10" to 12" deep half way around the tree?
Marion County Oregon forestry
To maintain tree health, it is best not to cut or damage a significant portion of the roots. Cutting the roots of your redwood at the dripline, half way around may pose little risk, as long as the the result is that you are only severing small roots (<0.5 inch dia let's say) and only a small fraction of the total root system.
The significance of the damage you are doing, depends on the full extent of the root system and the size of the roots you are cutting. Tree roots can extend far beyond the dripline, especially on larger trees.
How large is your tree? How far from the trunk would you estimate is the dripline? If possible, please continue this inquiry with me via direct email.
It is about 7' in diameter and I would be cutting about 15' from the base for about 35' along the edge of the flagstone. I may only need to go down about 8" but some of the roots may be 1.5" to 2". See pictures.
Given the large size of the tree and the area that is covered by the stonework, I would expect the tree is depending on a large portion of the absorbing root system outside the flagstone perimeter and under the grass. Cutting the roots at the flagstone perimeter down to 8 or 10" could sever a significant portion of the absorbing roots. Given the amount of foliage needing water on this large tree there is substantial risk of moisture stress to this tree if you sever those roots.
The portion of the functional root system that will be affected depends on what is on the other half of the rooting zone (behind the fence?) and on the depth of the soil occupied by the roots. It is likely that many of the important absorbing roots are shallow under the grass, which would be most impacted by cutting.
It would be best to minimize severing of these roots in order to keep the tree in good health. And if you must do it, avoid the dry summer season and do the work in fall to give the tree time to grow back roots before the next growing season.
Thank you, I'll wait until fall.