gigim,
What is your soil like? Is it sandy? DId you amend it at all?
Does it drain really well, with a gardenia, everything is about the soil you are growing it in.
When your impatients are about to end for the season, clear off the entire bed, dig down in the soil, and see what it is really like. Dig a hole about the size of the shovel head down, and fill it with water.
See how fast the water drains. If the water drains right through the hole, and within a matter of a minute there is no water in the hole, its draining too fast. If you still have water in the hole after 1 hour, you have to improve the drainage.
If the soil is really sandy, add composted manure and mix it in real good with your soil. That will improve drainage big time! I usually add a whole bag of composted manure per plant before I even plant anything. I mix it in with the native soil real good, and then I test the water drainage again.
If the water doesn't pour right out of the hole into the ground, then I am fine to plant.
If your soil is orange and doesn't srain well, do the same thing. Buy a big bag of composted manure and add that to the exsisting soil the same way. Make sure you mix it in real good. Plant your gardenia up on a mound instead of being the same level as the ground. This will help with the drainage too.
After i plant, then I water well, and then mulch like mad.
2 to 3 inches of pine bark mulch per shrub.
Wait til the weather cools down some before you plant a chuck hayes.
I love them, I have had a chuck hayes for 5 years. If is beautiful, and blooming now.
I also love August Beauty.
I have sandy soil, and now after years of adding composted manure and mulch, I have really good soil for my plants and lots of worms.
Don't put anything on your gardenia. Just a little diluted Miracle Grow in the spring when it starts to get a little warm.
People throw vinegar on them and god knows what else on them, you can kill a shrub doing that.
All it needs is really good composted soil with good drainage and lots of pine bark mulch.Pine bark mulch, nothing else, and a good drink at least once a week. That's all.
Yellow leaves are fine. Don't think just because your gardenia has yellow leaves there is something wrong.
Especially in the fall, all gardenias get yellow leaves, its normal.
Chuck Hayes are a little hard to find, so I hope you find one. They are also VERY cold tolerant, even though we really don't have to worry about that too much, zone 8 doesn't usually get too cold.
Watch your plant, when it wants water, the leaves will face up and ask for it.
Good Luck, hope something I wrote will help you.
Remember, if in doubt, with a gardenia, do nothing.
They are very hardy shrubs.
{{gwi:583057}}

I amended the bed with mushroom compost and soil conditioner when I created it in the spring. I will wait until the impatiens are done, remove them and test the drainage as you suggested.
Composted manure - better than mushroom compost?
I cannot find any locally and was planning on ordering online-Wayside Gardens perhaps.
Sounds like I might have done too much. Will take your advice and amend, plant properly, water weekly and leave alone.

The bark fines that Lowes/Home Depot sell bagged as 'soil conditioner' are generally very useful and mix into your existing soil more easily to hold/absorb and release moisture.

gigim,
Composted mushroom is fine. If your soil is sandy, its on the acidic side anyway. Composted mushroom, manure, composted leaves left to compost, all good.