Beginner Gardening: I am not sure what is happening to my lemongrass please help, 1 by Rachel1919

Rachel1919 wrote:
I have two of these in different areas. They had both been healthy and then both turned brown at the same time. I cut one back hoping it may help but I left the other one alone for now until I find out what I can doo to bring it back. The one in my garden is very large and when it turned brown it became rather unsightly so that is why I cut it. I'm wondering now if that was a big mistake. I checked on the plant today and the roots look good and there are no signs of pests or disease at all. Since it is in my garden it gets watered every day. I'll put a picture below. Oh what is Superthrive and where can I get it from? Is it possible that I may be overwatering it?