What ive noticed on older/woody stems is borers or carpenter bees, possibly, tunnel inside the stem and cause it to die. Usually the plants are so vigorous that you just prune out a stem here and there. If they are growing in rich soil and sun, you may want to just prune them all down to ground level every three years or so, and have fresh stems.

Ends of branches die when rhododendron or azalea borer larvae tunnel in a stem. This affects the portions of the plant away from the roots from where the borer larvae is in the stem. Borers have done their damage when you see the wilting and usually it is best to cut off the affected region. The requires removing the damaged branch from the hole where the eggs were laid at the base of the dying branch to remove any larvae before they become adults and infect more plants. The parts that are cut off should be destroyed to kill the larvae that are in them. Borers are prevented by following a spray schedule (timing is very critical) for borers with chlorpyrifos or lindane. Your county agent can help you with this information. Buds and twigs becoming covered with silver-gray scales is caused by the fungus Briosia and is easy to control with fungicide sprays and proper sanitation by removing and disposing of all dead material. Check with your county extension agent. Here is a link that might be useful: Common Problems & Their Solutions

I'd remove that red mulch in a heartbeat. Wait to summer's over and give it a real grandulated fertilizer. To me, the spikes just don't give a young growing tree what it needs. Also, are you planning on walking around this tree. I can tell you, mine has a 25' spread. You need to "limb it up" now when the lower limbs are still little. At least 4 feet. And don't forget the saying - buy 3 rakes. One for you and the other two for your neighbors. They throw down a lot of leaves! and this time of year, I'm raking up the old flower pods. Two garbage cans full this week........cheryl

I have wetlands at the back of my property. the soil is very clay like and the area usually won't dry up until may sometimes. I've planted smaller green giants there about 4 years ago and another areas as well from the same batch. the ones in the back have pretty much done nothing, growth wise and they are the first to bronze and the last to green up, infact some are still not all green. The GG's in different areas have quadrupled their size easily. so they may be tolerant to wet feet- but don't expect crazy growth. at least for me it didn't happen. Z6B