Question
I have 440 feet of an 11 foot canadian hemlock hedge I planted 20 years ago.  The hedge is about 6-7 feet wide and I shear it once a year at an angle keeping the base wider.  There is an increasing amount of dead wood on the interior of the hedge and a 3 - 4 inch build up of needles under portions of the hedge.  Should some of the needle build up be removed under the hedge. I have read the needles can be toxic to not only other plants but to other hemlock and I wonder with the contrived setting of a sheared hedge the breakdown of so many needles might be damaging to the trees.  There is also an increasing amount of dead wood on the interior of the hedge and I am wondering if I should try to prune most of it out. The hemlock are 3 feet on center so you can imagine this is a mammoth undertaking.  In some shadier areas where the lower branches have lost their needles I have pruned the branches out and have had success with other branches growing into the empty areas.  Any advice you can give me on maintaining a healthy hedge would be appreciated.  It is beautiful but is also a constant source of worry and stress and alot of work.  I am located just outside Portland Oregon.

Answer
As needles and branches get more shade as the tree grows the inner needles will shed and the branches die. This is normal. These dead branches can be pruned off and will make the tree look netter. Prune them back to about 1/4 inch of the trunk--this leaves the branch collar and the wound will heal over quicker. Leaving them is not a problem to the health of the tree.

The mulch will keep weed species from growing mainly due to the covering of the soil and not allowing the plants to sprout. I would guess this would be true for the hemlock that might grow from seed. But it is not toxic to the hemlock tree. A 3 inch mulch is about what you want. I would leave it as is especially if the needles near the soil are breaking down. The breaking down of the needles is good for the soil and the trees. Removing it will allow seeds from weed species to sprout.