Every once in awhile it happens. You have a plant that just takes a turn for the worse. It may be lighting, a weak plant to begin with or many other reasons but you can try this quick technique and see if you can save that plant. I have had a lot of success with it myself.
photo credit: mikewade
Take your plant and cut off all sick parts. Yes, you may only have a stick when you are done but we are trying to save the plant so cut off any weak or diseased parts!
Get some room temperature coffee and pour on the plant. You may have to dilute it some if the coffee is really strong. It may be the caffeine stimulates the plant or some nutrients in the coffee but this seems to give the plant a kick.
Place a plastic bag around the plant and secure it with a rubber band. What you are doing is making a mini greenhouse and giving the plant a nurturing environment. If you plant is delicate or easily damaged you may want to use small sticks in the pot to hold the plastic bag off the plant.
Place in an area that get some sun and let it heal. I check on it daily but leave it alone. This healing can take a few days or a few weeks. You will notice better color and new growth.
One week seems to be about the average for me to turn around a sick plant.
I also use diluted coffee on plants as a fertilizer in the spring and fall. For certain plants I will scratch a small amount of coffee grounds (teaspoon) into the top of the soil by the plants stem taking care not to disturb the roots.