I thought of fertilizer burn before you mentioned it.

I'd flood water the plants several times a day for 2 or 3 days. The water won't hurt the plants but will flush the excess nitrogen from the soil. Just make sure the pots have good drainage. You can't reverse the damage that is done but you can stop further damage this way. The plants should recover if they are not too far gone.

Thanks enjay. I actually think that you are right about the lack of water as opposed to fert. burn because the worst ones all had browning leaves on the bottom close to the base. I flushed them all with water just to be safe though.

When you water a containerized plant, it is important to fill the pot to the brim. Otherwise, you end up not leaching through the soil column and salts build up. Water heavily, then walk away and leave the darn thing alone until it actually needs water again, which in pots can be quite often. But don't water on a time schedule, water when the medium is dry.

willzbernard, from my observation, the yellowing of leaves in the summer is mostly reversible, so is the browning in the fall & winter. The tree loses its leaves once they turn red. Just to give an update on my pillars, so far theres no browning of leaves yet even with our areas freezing temps & wind. so youll be fine, they just need water.

last thought, i dug up one tree this past spring & found that their root system is very shallow. Some roots would go above ground, i guess they love the loose, cool mulch. some roots jump if theres a low barrier in the way. i think shallow roots are common in arborvitaes. this explains how easy they dry up if not watered regularly.

Concentration of most tree roots near the surface is usual outside of desert areas.

If the O.P. has 200 of these because they are growing them to sell I hope they are aware this is actually a patented invention.

http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1&f=G&l=50&co1=AND&d=PTXT&s1="american+pillar"&OS=

enjay, I am surprised that they need so much water even after they are in the ground for 2 years because that is not what the American Pillar nursery claims. The following is a quote from their planting instructions:

Watering

It is recommended by American Pillar Nursery to water American Pillar Arborvitae thoroughly so as to soak the root at least once a week for the first growing season. When using the drip line provided by American Pillar, it is recommended to water for at least 8 hours 1 day a week for the entire growing season. (March 1 through November 15). Twice a week during July and August if it remains hot and dry for any period of time. If it rains more than 1 ½ - 2 inches in a given week it won’t be necessary to water that week.

Water the following year during periods of drought. The Pillars will always enjoy watering but after the 1st year they truly become quite hardy.

Embothrium, I am aware of the patent. Between me and my next door neighbor we just put about 180 of them in the ground. So far they seem to be doing fine. the yellowing seems to have reversed, but on 20-30 of them I had a few branches dry out totally till red and then come off. Otherwise they seem OK. It was too much work for me to plant myself so I hired someone and I'm a little concerned he planted some of them too deep. I'll see how they fare.

Summer of 2014 was the best bec i really didnt water them at all, we had a wet one that time, & good thing to note, no heatwaves! The drought was really bad the past 2 summers in our area. I learned from the summer of 2015, when i found myself in the same situation as you right now. all my pillars started turning pretty golden at first then got worst turning to dry yellow. the worst were the ones in full sun.

i tend to my plants almost everyday & when i see the soil is too dry, i dont hesitate to give them a soaking, make that a heavy soaking. i noticed that with the drought, the soil dried up pretty quick, plus the long stretch of heatwaves in our area, no moisture in the ground remained. & to consider the shallow roots - i did pay a lot on my water bill.

Dont worry about losing some leaves or branches this time bec once you see the main/prominent leader maybe after 2 spring seasons, you have to remove the other competing leaders &/or suckers. but worry about this one later, just post a comment here when that time comes. for now lets hope we wont have another drought next summer.

In nearly all cases, one should not have to water a newly-transplanted tree or shrub more often than once per week. I'm suspicious of "over-care" when I see people talking about tending to their hardy landscape plants on a daily basis. They shouldn't require this. Now do realize, I'm generalizing here; Local conditions-wind, heat, drought-all impact this thing. But there's few situations where we would want to be watering our hardy landscape plants daily. Very, very few.

Recently planted potted stock with intact potting soil root masses can dry out rapidly during dry weather, due in large part to usually more finely textured natural soil having a greater attraction for water than coarse potting media. And if the plant hasn't rooted out well yet it is still dependent on what moisture is present in the potting medium, almost as though it was still in the pot.

The effects of textural differences on water movement into and through new plantings is probably the main reason bare-rooting at planting has become recommended in later years, and back-filling planting holes with unmodified existing soil has been advocated for some time - university level researchers having started noticing reduced response from trees and shrubs in amended planting holes by the 1960s.