How can I make a tree plant out of a gardenia plant ??
This article will help you.
https://www.gardeningknowhow.com/ornamental/shrubs/shgen/pruning-a-shrub-into-a-tree.htm
Your article is contradicting. This is what you have on your article. ("Fertilize monthly between April and November. Do not fertilize gardenias in the fall.") Fall starts in September. So can I still fertilize my gardenias in October and November?
Only fertilize into Oct and November if the plant is still actively growing. Avoid fertilizing when the plant is entering dormancy or is dormant.
my Gardenia in a large pot has been outside and starting getting brown in the centre of the leaves which then fell off. The leaf is green edged with yellowish centre - I then brought it into the conservatory but the same thing is happening - the white flowers are perfect - please any advice? thank you.
Lack of humidity is most likely a key issue. Gardenia are very finicky plants.
Here is a few articles that will help you.
https://www.gardeningknowhow.com/ornamental/flowers/gardenia/gardenia-plant.htm
https://www.gardeningknowhow.com/edible/helping-a-gardenia-bush-with-yellow-leaves.htm
https://www.gardeningknowhow.com/ornamental/flowers/gardenia/when-to-prune-a-gardenia.htm
Where should I place my potted gardenias outdoors? Morning sun? Afternoon sun? Full sun or part shade? Which side of the house SOUTH EAST OR WEST?
Gardenias in pots require bright light but also consistent temperatures and humidity. This article should help
https://www.gardeningknowhow.com/ornamental/flowers/gardenia/growing-gardenias-indoors.htm
There is brown rust like spots on my standard gardenias. What is the problem here and what should I treat it with?
It could be a number of issues ranging from stem canker to a type of mildew. If you're on well water: occasionally the high iron content in the water will literally stain the leaves. But this article may help you positively identify and correct whatever the issue is: https://www.gardeningknowhow.com/ornamental/flowers/gardenia/common-gardenia-diseases.htm
Where can I purchase an indoor Gardenia? Can Holly Tone be used for them as a fertilizer?
Check with local garden centers and floral shops for Gardenia plants.
These articles will help you with care and feeding.
https://www.gardeningknowhow.com/ornamental/flowers/gardenia/growing-gardenias-indoors.htm
https://www.gardeningknowhow.com/ornamental/flowers/gardenia/fertilizing-gardenias-in-your-garden.htm
I've recently moved to Hutto Texas and I've tried growing gardenias three different times. Each time the plant stems start turning black then it moves to the leaves and it within a couple days to plant is gone. I'm an avid Gardener I grow most things from seed. I just don't know what I'm doing wrong with my gardenias. They are my favorite flowering bush and I want to succeed.
Gardenia are a finicky plant! You are not alone in frustrations in growing Gardenia.
The black leaves could be due to root rot or even Sooty Mold that is caused by pests.
These links will help you review the care needed.
https://www.gardeningknowhow.com/ornamental/flowers/gardenia/gardenia-plant.htm
https://www.gardeningknowhow.com/ornamental/flowers/gardenia/common-gardenia-diseases.htm
https://www.gardeningknowhow.com/ornamental/flowers/gardenia/fertilizing-gardenias-in-your-garden.htm