Question
Hello,

we have a mature spruce approx. 40 yrs old in our backyard. we are building a retaining wall around it and while we were digging we had to cut some roots. now quite a few of the pine needles close to the trunk have turned brown. is the tree just in shock and will it come back? or will it eventually die? we've had a wet summer so it's definitely had enough water. thanks!

Answer
The roots of a tree will extend about 1 1/2 times the width of the branches. A tree can survive root cutting if the amount of roots cut does not exceed 25-30% of the root system. This includes adding soil over the root area or taking soil away from the root area. The root system can be measure roughly by drawing a circle around the tree where the ends of the branches hang and then estimate the area to be cut or filled and calculate the percent damage. The roots will extend further than the branches but these will be smaller and can with stand cutting.

The amount of roots cut will show up as about that amount of foliage dying. IF you added fill dirt behind the retaining wall this will add to the root damage. About all that can be done now is wait and see if the tree survives. I would expect that you will get some branch dieback from the damage but the tree will survive. I would next spring fertilize the tree with 10-10-10 fertilizer scattered around the tree and watered in good--apply the fertilize just before a rain storm and you will not have to water.