they are conifers..

but also trees...

there is a very active conifer forum.. wherein you would learn.. that ALL INTERIOR BROWNING IS NORMAL...

no conifer holds its needles forever.. all 1 to 3 years ... all interiors of conifers are nudey ..

never feed a conifer.. especially at planting.. you dodged a bullet there...

after two summers.. they should be free range.. and NEVER need to be watered again ... unless you are rather inclined in some severe drought ...

if they are within their height from a fertilized lawn ... the root mass.. which is at least as far as the tree is tall and maybe up to twice such.. will get some fert from the lawn ...

ignore them other than to gaze at them.. try not to kill them with too much love ...

post a pic in the conifer forum if you want to verify what i said ...

good luck

ken

ps: as it is normal.. one might suggest your title is a bit dramatic... hence the suggestion not to love them to death reacting to something normal ....

"Each of them were about 3-5 feet when I purchased them, and 2 years later they are about 5-6 feet."

There are lots and lots and lots of unknowns presented in your post. One such missing detail is whether your GG's were B&B or potted. Either way, with a 5' GG, one would expect a very large rootball/pot. It sounds very possible that your trees have not become established yet. By choosing 5' specimens, you gained height at first but are already paying for that in lost growth / slower establishment. Withing just a few years, an originally smaller tree would probably be outgrowing your relatively large ones. Eventually (assuming there's no problem with your GG's), they will become established and begin to grow at normal rates. Generally (because or rootball/pot size limitations), the larger the tree is, the longer it takes to become established and start growing significantly.

As Ken says, some internal browning and needle drop is normal. Also, GG tend to turn a little off color during colder months (at least in colder areas...not sure it would normally be as significant in zone 8). Pictures might give us more info about this part.

Ken already said it, but STOP WATERING!!!!!

Would be interesting to know planting details. See link below for planting info.

Here is a link that might be useful: Planting a Tree or Shrub