How do I get grass rhizome to spread into bare areas?

Plants have certain times when they do certain things. For example, each year a perennial plant will try to reproduce itself and put energy into making seed. This is when they become stemmy. The same is true for rhizome production. We usually see rhizome production most active in the spring and in the fall; mostly in the spring. If your bare spot is bigger than 3" in diameter, consider adding some seed, as open spots can become home to weeds faster than the surrounding grass plants can fill in that large of a void.

There are reasons why bare spots exists. For instance, there may be problems with the soil in that area, which either prevents grass from growing or makes it difficult for it to continue to live. Take a look at your bare spots and see if there are obvious issues with the soil. If not, and if the spot continues to either stay bare or become bare again each year, consider replacing or amending the soil.