[Marco]

We are going to be installing a sprinkler system thru-out our entire 1/4 acre lot this coming fall. We have lots of lawn and big flower beds to irrigate, but the problem I "know" we will run into once we start our project is TREE ROOTS.......and LOTS of them. There are 5 old growth very tall cedars, 2 old growth very large firs, 1 old growth very large cherry and 1 old growth medium apple trees scattered on our lot (the bulk being in our back yard and 4 of the ceders are tightly spaced with approx 20 ft max between some and 6 ft max between others) Once we chart the course for our sprinkler system lay-out, I know, after pouring a big driveway on this lot and digging deep fence post for a custom bamboo fence, we are going to run into massive amounts of tree root, with a lot of it high on the surface thru-out the lot. QUESTIONS: Is a full lot sprinkler system feasible on a lot with this level of tree & root growth? Are we going to damage or even kill some of these trees by hacking into their root sysytems to get the trenches dug for the sprinkler system piping? What do you recommend we do? (as far as the smart / best way to get our sprinkler system in but not damage or kill the big old growth trees? THANKS for you insight and vast knowledge !!

[MountainShe]

Large established evergreen trees can be fatally damaged by root injury. Trenching through the feeder roots in the first 18 to 24" of soil is a really bad idea. These trees put out a root system that can extend three times the height of the tree.
Sounds as though you have already done damage by previous work around them. unless you want to loose them, I suggest you keep your trenches and lawn away from the trees outside canopy at the very least 25'. You may not see the trees start to decline for a a year or so after the damage is done, but decline and weaken they will and you are taking a big chance on killing them.
Also remember this, trees raise property value a lot more than a lawn and planting beds do. You loose those trees you loose value in your property plus have to pay thousands of dollars to have then taken down once they die. It is a no-brainer to me.l I also have fully mature huge Cedars in my yard, I do not have a lawn and my planting beds are raised in planters to protect my trees roots and to protect the plants as well.
If you plant in the ground you will find the tree roots strangling your plantings in a few years anyway.