My guess would be transplant shock. Give them some more time to establish some new roots. Did they fruit while in the containers? I would have just got a couple of new young trees then mess with giant rootballs :)

Just wanted to post a followup on this for anyone who may come across this thread in the future. I always hate finding a thread full of good information, but then not knowing if it actually worked or not. I replaced the trees that died, and the new ones are doing great. Here's what I did differently. (I know that for some of you, these may be the most obvious things in the world, but some of us are still learning, even from our really stupid, obvious mistakes). - I waited til it cooled down. It got cooler earlier than I expected, so I was able to do the transplants a couple weeks ago. - Smaller trees. I did still really need the height, so I went with 6-8' tall trees (some are about 9', actually), but I got much smaller caliper (trunk diameter) trees. I tried for no more than about 1.5" caliper, measured 6 inches above the root flare (some are a little closer to 1.75"). They're definitely much less full, but they'll get the job done until they fill in and grow up a little. It helps a lot that I found out that for screening purposes, eastern red cedars can be planted as close as 4' apart. Bigger, fuller trees really aren't needed at that spacing. - No starter fertilizer. These are trees, not grass. I used some Fertilome Root Stimulator & Starter solution (per the manufacturer's instructions) when I planted, and may add some Superthrive in a couple weeks, just to get the roots really going before winter kicks in. - Much better care of the root balls. I didn't make perfect root balls, as such - after reading a whole lot of back and forth between scientists on the benefits of good root balls vs taking as much root as possible, even if they're outside of the dirt, I kind of went with a hybrid approach. I got as much root as I could, and kept as much dirt on them as possible. I kept all of them covered with dirt of some type for as much time as possible, and ensured that they never actually got dry. Total time from digging to planting was less than 4 hours, and most of that time, they were in some kind of dirt. - I watered with a sprinkler for a few days, to let moisture come in through both the roots & leaves, in case the roots were having difficulty of some kind. Then I found out about Wilt-Pruf (prevents moisture from escaping through the leaves, which causes a lot of transplant shock). I applied it per the manufacturer's instructions, and am now watering with a soaker hose, as Wilt-Pruf should also prevent absorption of water through the leaves. - I haven't mulched yet (life got in the way unexpectedly), but I will be soon. Something else I came across in my reading - mulch isn't required, but most bushes or trees that are mulched in their first year or two after transplant show 20%+ more growth than those that aren't. Since growth & size are my primary goals here, it's worth having that junk in my yard for a year or two. We'll see what, if anything, will grow under these trees once they're established, but for now, it's gonna be mulch. Thanks, everybody, for all the insights provided. Hopefully these results, and what I did to get them, will be useful to someone else in the future, too.

I had no idea these plants were so expensive. I am raising them from seed to hopefully plant around some property  they are a beautiful tree. The nice thing about these trees is they can live a long time; I have read about 4000 years. Because they are in the agave family or related to the agave they should be easy to maintain. Your link did not work, but these trees are in some California parks & are fairly common in the desert gardens of botanic parks. Mine are still at the seedling to 1 year old stage. I have noticed they do not like sand. I have some in soil & some in peat  the ones I have not taken out of peat yet are doing the best. Like Alejandro1 said they do have medicinal qualities. I have medical books from the 1600Âs which speak of the use of this tree.

This is from Deborah Silvers's blog "Dirt Simple" : a short story of the first tree she planted. Also excellent photos of transplanting a huge tree with a tree spade. http://www.deborahsilver.com/blog/planting-a-tree/#comments If any of you like doing decorative containers, this is the blog to follow...she's a master of the art. Marie