Answer: You really love a challenge! In addition to the acid/alkaline situation (some plants like acid soil, others like alkaline), you have put high moisture/low moisture plants together making watering a problem. One thing you didn't mention is the pH of the soil. If it is about 6-6.5 most of the plants should be fairly happy.
My first suggestion would be to focus on the plants most important to you. If you can't get all to thrive, get the ones you love best. (Watch out for that asparagus fern. It is an invasive, difficult to erradicate plant!)
Could that rosemary be put in a large planter somewhere? Or, could you raise the spot in the bed where it is growing? This will give it good drainage even when the rest of the bed is on the wet side.
Does the gardenia have lots of compost or peat in its planting area? If not, plan on lifting and resetting it in late November (if things are not better by then).
I think some fertilizing will help many of your plants. Compost, liquid plant food (a quick, but temporary fix), and slow release fertilizers are available to help plants get nutrition and promote bloom. To help lower pH spread 2 tablespoons of sulfur dust evenly beneath the branch spread of your gardenia, and water in well. Fertilize it with an acidifying product like azalea/camelia food.
Keep your plants well watered but not soggy. And hope for the best!
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