From my book titled "Ornamental Palm Horticulture": Powerline decline shows chlorotic leaf tips as well as necrotic leaf tips that hang down (the picture looks like 1/2-1/3 of the end of the branch is either yellowing or crispy and hanging at a 90 degree angle from the branch). I don't see any coconuts on your tree. You said it dropped the fruit; it is most likely Lethal Yellowing...your tree appears to have some of the symptoms. If not LY, your tree looks like it has K-deficiency (potassium). Manganese deficiency usually causes "frizzle-top" (in queen palms), or misshapen, curly leaves in other pinnate palms. Unfortunately, it appears as though your palm tree has lethal yellowing. : (

The picture of your dwarf coconut tree looks nice there. It has healthy looking fronds. I wonder if it's just a dwarf, or is it really sick? So, were you able to get fruit out of it all the 10 years you've had it? Thanks for the link to the Indonesian website. They do have a lot of healthy looking coconut bonsai. I'm still trying to find out if they actually will produce fruit eventually. I've looked at some bonsai fruit trees on the you tube and they seem to be able to flower and produce some fruit. It would make a lot of sense for people like us to consider having bonsai trees if we cannot be sure that we can keep these tropical plants alive in the ground. You sure are a lot closer to the equator than where I am. You're over 800 miles and I'm around 2,500 miles off the equator. It's nice that you have the warm enough temperature to keep these beautiful trees there. So, do you have to manually irrigate your your landscape, or do you have an auto irrigation? It would be a lot of land to irrigate as you seem to have a huge place there. So, what do you do when your trees produce all the fruit there .. lol? Do you eat them? Do you know that coconut is known as the miracle fruit? There have been many articles and books written on it. A few years back, I started changing my cooking oil to coconut oil and include coconut milk and flour into my diet. It has brought tremendous improvement to my health situation. I've heard that coconut water is also a super nutrient drink, but I have to read more about it to find out if it contains a high sugar content which I'm trying to avoid. There's even someone on the internet selling fresh coconut water online.

I know someone growing a coconut out of zone. He had it covered with plastic during winter until it got too tall. At this stage he has stones on the ground around the trunk and that's covered by plastic to keep the heat in and rain out. He's not expecting many more years out of it now. His climate is dry summers and wet winters. There's enough sun in winter to heat the stones to warm the ground. Rarely gets frost, but before each winter he agonises over the long range weather forecasts as to whether it will bring a frost. This winter (now) he's been quite happy as there's been no frost and unlikely at this stage. I'm sure, even though he denies it, that when this coconut dies he'll end up getting another one and go through the same process again. It's given him a lot of joy, and a lot of challenges, for quite a few years.

You must have been using some large/hot lights if they were the cause of the die back. Were your lights on consistently throughout the season, or were they used sporadically. Is it possible that your environment was warm enough to encourage active growth which then got burnt when the lights and heat were turned off? A plant might tolerate a particular cold temperature in a dormant winter stage, but expose the plant to the same temp in the growing season, and it can outright kill it. I would NOT be watering it or feeding it at all this time of year by the way (normal rain and snow should be enough). Even if the palms do not die outright from whatever the cause was, they did take a big hit obviously and this will make their winter survival this year all more questionable. Growth for the coming growing season may also be stunted compared to normal (vigor will increase in subsequent years). But many palms can and DO SURVIVE from pulled buds.(I've had successful recovery from bud pull on Phoenix roebellini, and Washintonis in the past--one from cold, one from excessive summer rainfall.) Frankly, if they were mine, I'd be tempted to dig them out (don't know if your ground is frozen or not), containerize them, protect them from hard frost, give them an early start on the growing season, and see if they recuperate--betting that they would eventually. Good luck!