Gardenias are a bit difficult to root without a misting system.

Best time for taking 5-6 inch cuttings is probably the summer. Cuttings should have three or four leaves on each, which you should not remove, if you have a mist system.

Sand, perlite and sand, perlite and peat would all be good rooting mediums to try.

Here is a link that might be useful: General propagation guide

Jakedog, thanks for asking that question. I have a huge
gardenia over in Mauriceville, Tx. The place sat empty
for years and the last time I was there I found that a
huge sweetgum tree has grown up right in the middle of it.
I'm hoping that when I eventually get to move back there
I can take starts off the gardenia to transplant elsewhere.
Will probably kill it trying to get the sweetgum tree out
of it. Was a huge beautiful bush tho. I used to pick some
of the flowers off and put them it dishes of water all over
the house as they smell so good. I'm living in Mesa, AZ
right now and its way to hot here for gardenias.

Let us know how the rooting does for you.
I have a huge hibiscus here and when I find a low branch
I bend it down carefully and notch it where it will be
in the ground. dig a small hole and fill in dirt around
it. Place a rock on it to help hold it down. I've root
several this way. You might try that with the gardenia
if you have some low growing branches.

Pam