Q.My citronella plant is turning brown and dying. The leaves are turning yellow then die off, also it seems to look like all of my s
tems are turning brown? Am I watering them too much?
Water management and drainage is important. Yes it is possible to water too much and cause root rot. I'm not sure if that is what is happening with your plant.
Here are some articles and product examples that may help you with creating better conditions and maintenance.
https://www.gardeningknowhow.com/edible/herbs/scented-geranium/mosquito-citronella-geranium-plant.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm
https://www.domyown.com/luster-leaf-rapitest-mini-moisture-tester-1810-p-7732.html
https://www.domyown.com/dr-earth-organic-all-purpose-fertilizer-p-9485.html