Do they get enough sun?

 

I suspect as they have grown they have begun to shade each other out. You could try some tree spikes and see if that gives them a boost.

https://www.amazon.com/Wetsel-Jobes-Evergreen-Spikes-Value/dp/B018YM3OA8/ref=sr_1_11?crid=1QEROH5UXZ6MJ&dchild=1&keywords=jobes+tree+spikes&qid=1585417980&sprefix=jobes+tree%2Caps%2C143&sr=8-11

 

Have they had bagworms?

 

See deer in your yard often? Looks like they found something new to eat on....

 

Have they had bagworms?

+1 on this. Bagworms are a huge problem at my place especially the Arborvitae

 

Just wanted to update this post...
Had a professional come look at them and he advised me to treat them and fertilize them.
I spray twice and fertilize once a year and this is what they look like today...
Sorry the photos are a bit cloudy, cracked the lens on my phone...

 

That is a remarkable improvement. What are you spraying for?

 

What are you spraying on them?

Just an all in one spray each season..
I have used BioAdvanced and Bonide brands from the local nursery. They recommended it as well. Great thing about the local nursery you can bring in samples of the leaves/soil and thy will test and get you what you need at no cost...
just the cost of the spray/fertilizer of course...

 

Thanks for the Arb tip. They're pita to bring back once they start to get leggy. I'm going to try this myself next time I encounter something like this and see if it works!

Hall's Landscaping
Servicing Arlington And NoVA Since 2008
For Landscaping In Northern Virginia

 

Came across this thread and hoping u can explain further please. Did you spray the bio advanced in spring and fall and then what fertilizer did you use and how often? I’m desperately trying to save my arborvitae . Thank you!