(September) Every year, I plant a lot of basil. I plant in the front yard that
gets sun from noon till sunset, and in a pot in the backyard that gets sun all
day long. I feed them every week or two. By midsummer, the stems begin to harden
off and turn brown to black, at which time, of course, the plant is dead. What
is my problem? I pick them often but not constantly. I pick from the top,
usually.
When you say harden off, do you mean the stem gets woody or when it is black or brown does it feel soft to the touch? Basil is usually a pretty tough plant, but it can suffer from root rot. Fusariam wilt is another disease that can attack it. This disease will usually lead to a pretty quick death once it hits. The disease is soil-borne, so crop rotation is important. I can't imagine having it in a container however, especially if you use fresh potting soil every year -- which you should. Let basil dry out slightly between watering, and make sure to plant in a new location and see if that helps.