Two years ago I tried Lemongrass oil on my toe nail fungus and all it did was to make my nail color go black. It never worked. I had a black nail for months also the nail was curved due to the amount of fungus under the nail.
I finally got it to clear up by using Iodine and Castor Oil applied to the nail and over time the new nail grew in clear and the problem has not come back.
Lemongrass Essential Oil
There seems to be a lot of confusion about using Lemongrass oil for nail fungus. I too decided to try it last summer. I had never used essential oils before and was ignorant about proper dilutions. I applied the oil straight out of the bottle to all my nails on both fingers and toes. I applied it twice a day for less than a month. Then I started to have a reaction: I got a very bad rash and had degloving of my fingertips. I was very discouraged because I saw my nails growing out healthy. I stopped that treatment and am now using a diluted blend of different oils (will report back if this new blend works--so far so good).
However, if you wish to try Lemongrass oil, here is how to Properly Dilute the Essential Oil:
Pick a carrier oil such as coconut or grapeseed oil. Measure out one ounce (30 mL) of your carrier oil and add 12 drops only of the essential oil. This will make a 2% dilution.
Never apply undiluted essential oils to the skin until you are sure you will not have a reaction. For nail fungus, it is common to continue applying the oil treatment until the nail is completely grown out: up to a year. So be sure you are not allergic to the oil before you commit to using it!