Question
I have two gardenias planted beside the steps leading up to my front porch (they're approximately two years old).  One is thriving, the other is not.  The one that is thriving has the following (external) characteristics: it receives partial sun in the morning and the excess water that gathers beneath the plant (since the clay soil doesn't drain well) is allowed to drain away per a french drain.  The gardenia that is doing poorly (leaves wilted, very little root growth) has the opposite characteristics: little to no direct sunlight and the area beneath it does not have a french drain to help with drainage; the whole bed in which this poorly-developing gardenia is constantly moist.  

I need some help finding a plant similar to gardenias but that is a water-loving-type of bush requiring little to no sunlight; and preferably a species that would grow three to four feet tall.

Any help is appreciated.  I live in Texarkana, Texas.  

Answer
This is a tough one, Daniel. I have sent this answer three times, and it has not gone through. So, I will make another attempt to remember what I wrote, and hope for the best.

The first thing I would do is "fix" the soil. The problem with wet soil is, the water removes the oxygen in the soil. The plants need that oxygen around their roots to survive. With out the oxygen, they drown. Most good soil has enough large particals in it that it will drain. But, clay soil is made of very fine pariticals, and when these become compacted they do not drain freely. So that is what is happening to your gardenia right now. Couple that with low light, and it doesn't have a chance.
To fix the soil, you will need to get some compost, peat moss, and potting soil with a lot of loose material in it. Mix it into the soil where you want to plant, about a foot or more down. Then, build up a raised planting area about a foot, or more above the grade. This will give the plant roots plenty of room to go to avoid the area where there isn't any oxygen. Let the soil dry some inbetween watering. If possible, create a drain, to move the water away from the plant, when there is heavy rain.
But, that wasn't your question . . . You would like to know what to plant. Well, full shade, 3 to 4 feet high, simular to a gardenia, and water-loving type, that really narrows the list. I really have no garentees. But you can try the follow plants that I know are close to what you want.
Skimmia is an evergreen shrub, with white flowers, in spring. Does well in full shade, and moist, clay, soil.
Rhodedendron will take some shade, and moist soil. It has shallow roots, so if the surface is well drained it will be fine. Azaleas are a close relative, and would be more in the size range.
Camellia is another, but look for the dwarf variety, or prune. They will get tall like many of the rhodedendrons.
Hosta are a popular shade plant. But they are not evergreen, like the others and are not like a gardenia.
Pieris floribunda is another shrub that will tolerate shade, and has white flowers in the late spring.

So, you should be congratulated for having a gardenia that has survived. Many expert gardeners, including myself, have not had such luck. Don't be alarmed if it suddenly dies one day. They just do that for no particular reason.
bakerplanter