My two year old cactus is turning brown from the bottom. It is kept on a windowsill and is watered once every one to two months. It is not mushy
Welcome to the Forum! Without a pic, hard to say for sure, but sounds as if your cactus might be undergoing the natural process of 'corking'. Give us a photo if you can. There are several members (hey, mandarin!) who are quite knowledgeable on cacti and would undoubtedly be able to give you good advice.
Yes, could be corking, but it is rare on cacti that are just 2 years old. I have seen at least one kind of disease that makes the stem turn brown without making it soft, however. A photo would help.
