You have described the symptoms remarkably well. That the yellowing is moving upwards indicates that the tissues which conduct water and nutrients have been damaged. You have seen that the bark is peeling near the base (not a good sign) but there is a green layer underneath (a good sign). The bark near the base has been damaged either mechanically (trimmer line?) or there is a pest/disease at work. If the bark is damaged all the way around the trunk, that may well cause the whole top to die. If a part is still intact, and there is no disease or pest, the plant can recover and eventually heal itself. If it is a disease like canker, there may be no hope. If the whole top dies and there is new growth ABOVE the graft union, you can grow/train one of them into a a new plant. If the new growth is BELOW the union, the growth is from the rootstock and this is generally not aesthetically pleasing. If the black stuff is more like soot rather than black dirt, this is a sign of sooty mold fungus which in turn is a sign of insects at work. Look on the palm, gardenia and others for scales, aphids, mealy bugs etc. With your powers of observation and ability to express what you see, you should make an excellent IPM scout. It has been a real pleasure.

Wow, thank you. Black soot or ash would have been a better description... can the palm be treated? I guess that depends on what I find.

As for the damage tot he trunk of the tree it is not mechanical. It looks as though either the brown bark is flaking off to reveal the green surface or maybe the green surface is growing on top of the bark. It doesn't look like moss... it truly looks as though the bark is flaking off.

Thanks for all your help

That green layer just below the bark is where all the action takes place. It contains the tissues that take water and nutrients up to the leaves and the products of photosynthesis to all the parts of the plant. Bark tissue protects this vital layer and it looks like there is an insect or fungus at work on the trunk of the gardenia near ground level. Unless this action is stopped, the plant will most likely die. There comes a point in the IPM process when human intervention may be necessary. You have reached that point where the gardenia is concerned.

Your gardenia shedding leaves may or may not be of concern. This time of year, mine is doing the same thing--turning leaves yellow and dropping them, while healthy, new leaves are simoultaneously forming at the buds. It has been doing this for at least a couple of weeks and still isn't done. Hopefully, yours is doing the same thing.

Definitely keep an eye on it, and post pics if you get a chance. Would you be able to take leaf and bark samples to the nearest Cooperative Extension Office? They can tell you exactly what it is and what to do about it. And, for the very reasons that Ronalawn82 mentioned, the bark should probably be your biggest concern.

The sooty mold is normal to an extent, and is only there because of insect honeydew. Lately, the ladybugs have been emerging and the problem may go away on its own if they can take care of the aphid, scale (or other) problem. The mold itself isn't the problem, so just worry about the insects.

Good luck :)

I planted 5 gardenia bushes last summer. They looked really healthy for a short time. Insects of some sort, I know, was a culprit. I treated that problem but this spring, they don't look healthy at all. The leaves actually look like they are burning and drying up. I fed with miracid. The branches are not dead. They bend, don't break. Just really kinda dead looking leaves and I don't really see an abundance of new growth. Is there any hope?