I have a redwood in my backyard. The yard is mostly upslope (20 degrees or so), except where it is terraced. The redwood is about 70 feet tall and 4 ft wide at the base. I'm wanting to expand the terraced section that redwood sits on. The terraced area is presently 20 feet deep (50 feet wide)and i'm wanting to expand the terrace to about 40 feet deep (add 20 feet of depth to the flat terrace). That means i'll be adding a retaining wall around 35 feet downslope of the redwood (two feet in height) , and cutting into the ground and adding a three foot retaining wall around 6 feet upslope of the redwood. It's the upslope retaining wall that concerns me, which is kind of close to the tree. So here are my questions. Do redwood roots slope upward and grow uphill on upslope areas? If i cut into the ground upslope of the redwood at the same level as the ground that the redwood sits upon, will i likely hit roots? Will the retaining wall threaten the redwood? I don't want to lose the tree, and I definitely don't want it to fall on my house, which is only around 30 feet away (downslope of the redwood). Any insight would be greatly appreciated, including a website i might turn to for detailed info about redwoods on hillsides (if one exists). Thank you, Larry
Both cutting into the slope above the tree and adding a terrace down the slope from the tree will have a negative impact on the roots. The roots do venture both uphill and downhill and you'll find by cutting into the slope only 6' from such a large tree, that you'll be cutting into some fairly large roots. Besides stating the obvious on its stability, the loss of roots in a 'summer dry' climate could cause irrepairable stress. The downslope work is not going to have as great an impact but adding significant (>4-6") of soil over tree roots impedes their ability to access oxygen and can kill the roots. Stability is not such a concern but the dead roots won't be supplying nutrients or water to the tree either.
Thank you for responding smives. I did some exploration (some light digging), and though it wasn't complete, I didn't find any major roots uphill of the redwood at the elevation which i'd be cutting into the hill. So, does this mean that I probably wouldn't be damaging the tree by cutting into the upslope? Re the area downslope of the tree, I'd actually be adding 18 inches of dirt. So, the roots would effectively be 18 inches deeper. You seemed to think that 6 inches could do harm to the tree, so i'm imagining that adding 18 inches of dirt could do great damage. Is there anything i can do to minimize the damage, such as watering that area of the root system every few days during the summer? What if i don't compact the dirt? If i really want to have a flat area in my yard and don't want to destroy the tree, do you have any suggestions? Thank you again, smives. Larry
Finding it hard to envisage what you want to do. A diagram, and use of more readily understood measurements, would help. Trying to work out what all that archaic imperial stuff means doesn't help at all!
Ah Michael I must be showing my age I can work in both. Our big metric change over came half way through schooling. The two measurements are still used here. Recently even saw it in an add. The older generation are in feet and inches and the rest are metric. :) Liz