I live in E. Central FL..There is a spot that is shady ALL the time..I have ferns, Impatience, and some ruella there, but none of them look very happy..The rest of my gardens are doing very well, so I do need some advise for this one !
You didn't describe what "not very happy" looks like, but I suspect that if ferns, impatiens, and ruella aren't flourishing in your full shade spot, either the soil doesn't drain well and the plants have wet feet all the time, OR the soil pH is wrong. I'm leaning more toward too much moisture.
I would suggest buying an inexpensive soil moisture meter (I have this one--http://www.treehelp.com/itemdesc.asp?ic=LL-1817 which I purchased at WalMart for about $14. This model also tests soil pH). If the water content of your shade garden is too high, you'll either need to remove the plants, amend the soil with drainage material, and replant OR remove the plants and build a raised bed, then replant.
Another problem with a shade garden is lack of air circulation and slow moisture evaporation from leaves. Impatiens especially need good ventilation to prevent mildew and rot. Thin the plants to about 6-8 inches apart.
I hope this helps. Let me know what you do and how it works out. Good Luck!