Good morning! :) You sure have come to the right place, no worries.
It looks like stress to me. While they may be getting the same care, and growing in the same, or similar, conditions now, who's to say what was going on with them when you first bought them, ya know? Check way down into the root system to make sure it's not water-logged, to start with, (not to mention root-bound). Massage the container (if it's pliable), to loosen up the soil "ball from the container" and, while holding onto the main stem down near the crown, tilt the planter and ease the whole thing out and examine the soil (wet? dry?), and the roots. If it is installed directly into the ground, use a SHARP gardening tool (shovel or spade) to dig around the root ball, a good foot-and-a-half away from the root ball as you remember it when you installed it, and down as close to a foot as possible BELOW where you know the bottom was when you installed it. Get the shovel or spade under it and gently "pry" it up so you can inspect the roots and the soil. Again, looking for overly-wet or dry soil, and looking to see what colour the roots are (you want 'em to be white or pale yellow), and making sure the roots are not all wound up tightly,... or maybe eaten off by a vole!?!? EEEK!! While you're in there, also check to make sure you don't see any nasty buggy creatures that don't 'belong'.
Micro-climates in our gardens are funny things; what may do well in one spot won't necessarily do great just 2 feet away. The soil might be more compacted under/around that one than it is under and around the other one, or any number of other things.
Even though Gardenias bloom on "old wood", (which means that the time to prune them is after the blooms fade in the summer), I would suggest a pruning now anyway, especially to see what the wood looks like under the bark. (or, you could just scrape back some bark to see what the wood looks like underneath. You want green. White or pale yellow indicates stress, brittle brown means big trouble or already dead). If you prune, make sure your pruners are CLEAN first, by giving them a good rinsing in rubbing alcohol then letting them dry before pruning. Just prune back the affected-looking parts. Water deeply if you've found the soil to be dry, and give it a good feeding. It may just need to be babied a little bit. Whether it needs water or not, give it a good organic feeding. I can suggest one fertilizer that I know of that is organic and DOESN'T need to be watered in, and that's Dr. Earth LIFE fertilizer; totally organic, and just sprinkling it around the plant on the surface of the soil is enough, though you can gently work it into the loosened up soil with your fingers if you want. I'm sure there's loads of others that other members here could recommend to you, but that's one that I use... a lot! =)
Just a thought... is it possible that something is shading the other (healthy) one just a bit more than this troubled one? Are you able to check it out all throughout the day, to see how much sun it's getting all during the afternoon?
Based on the fact that it doesn't look like I see anything **on** the plant itself according to the photos, and you haven't said that you see any discolouration on it anywhere (other than the leaves being slightly yellowed, that is), that's all I can think of off the top of my flat head! < =D
I hope this is of some help to you Donrull. Please check back in and add any other info that comes to mind so we can help you as best we can.
=)
This message was edited Mar 15, 2012 6:47 AM
