Newly planted cedar hedges dying/turning yellow
Need your help.... I purchased 65 black emerald cedars from Homedepot, here in Montreal, in early June. Out of 65 cedars that I planted, 15 of them show signs of death/ turning yellow, as you can see in the pics below.
Note: Hedges are from evergreen propagators limited in BC: http://www.evergreenpropagators.com/
I believe I planted them all correctly - dug a trench 12-15 inch deep and 15-18 inch's wide. I planted my cedars 20 inch's apart from each other. I used Vigoro triple mix garden soil for the base of the trench and planted my hedges straight out of the pot. I used soil mixed with sheep manure to settle the hedges in place. Once I had all the hedges planted and in place, I watered them well and used Vigoro fertiliser for shrubs, and placed the fertiliser spikes at every3 feet along my trench as directed.
I continued to water my hedge for 3 weeks and onwards after I planted them and then used cedar mulch to cover the base of my hedge - keeping the soil nice and moist.
Fast forward to today - 15 cedar hedges look like they're done living, under the mulch the ground is moist and there is no animals or dogs that have been in my yard. I also verified if there was any bugs or insects that can be causing the issue and I see none. Can anyone give me any recommendations as to what I can do to revive these hedges? Is this normal? Should I be worried?